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ries on the diamond sutra and sutra of perfect enlightenment jinul korean seon monk one one five eight one two one zero founder of modern korean gong an meditation system simsang eight th century korean monk who at the request of r ben helped transmit hwaeom to japan thereby founding the japanese kegon tradition uisang seven th century korean monk founder of hwaeom tradition based upon the chinese huayan school weonhyo six one seven six six eight korean monk prolific commentator on mahayana sutras wonchuk thai somdej toh thai monk specializing in magical amulets phramonkolthepmuni one eight eight five one nine five nine thai monk who founded the dhammakaya tradition khun yay mah ratana up sik chandra khonnokyoong one nine zero nine two zero zero zero thai nun who founded wat phra dhammakaya historical rulers and political figures ashoka the great mauryan emperor of ancient india brhadrata the last ruler of the mauryan dynasty menander pali milinda two nd century bce an indo greek king of northwestern india wh |
o questioned n gasena about buddhism in the milinda pa ha kanishka ruler of the kushan empire sh toku five seven four six two two crown prince and regent of japan liang wudi five zero two five four nine emperor during the chinese liang dynasty harshavardhana six zero six six four eight indian emperor who converted to buddhism wu zetian jayavarman vii one one eight one one two one nine king of cambodia mongkut king of thailand and founder of the thammayut nikaya modern teachers theravada vipassana teachers ajahn brahm one nine five one ajahn chah one nine one eight one nine nine two ajahn mun one eight seven zero one nine four nine ajahn sumedho ven ananda maitreya one eight nine six one nine nine eight ayya khema one nine two three one nine nine seven bhante henepola gunaratana one nine two seven bhikkhu bodhi one nine four four buddhadasa bhikkhu one nine zero six one nine nine three dipa ma one nine one one one nine eight nine dhiravamsa phrarajbhavanavisudh luang phaw dhammajayo b one nine four four presid |
ent of the dhammakaya foundation phrabhavanaviriyakhun luang phaw dattajeevo b one nine four one acting abbot of wat phra dhammakaya thailand s n goenka one nine two four joseph goldstein nyanasamvara suvaddhana born one nine one three the one nine th supreme patriarch of thailand ven ledi sayadaw one eight four six one nine two three mahasi sayadaw one nine zero four one nine eight two sharon salzberg sayadaw u pandita one nine two one u ba khin one eight nine nine one nine seven one tibetan buddhist teachers chagdud tulku rinpoche one nine three zero two zero zero two ch gyam trungpa one nine four zero one nine eight seven dhardo rimpoche one nine one seven one nine nine zero dzogchen khenpo choga rinpoche one nine six five erdini qoigyijabu one nine nine zero one one th panchen lama according to people s republic of china government jigdal dachen sakya one nine two nine co founder of sakya monastery four one st generation sakya head of the sakya school in the usa kalu rinpoche one nine zero five one nine e |
ight nine namkhai norbu rinpoche one nine three eight paltul rinpoche one nine six five pema chodron one nine three six reginald ray tarthang tulku tenzin gyatso the one four th dalai lama thrangu rinpoche one nine three three trinley thaye dorje one nine eight three regarded by many as the one seven th karmapa see also karmapa controversy tulku urgyen rinpoche one nine two zero one nine nine six dzogchen mahamudra and the new treasures of chokgyur lingpa chokling tersar urgyen trinley dorje one nine eight five also regarded by many as the one seven th karmapa see also karmapa controversy zen teachers japanese kodo sawaki one eight eight zero one nine six five dainin katagiri d t suzuki ven hakuyu taizan maezumi r shi one nine three one one nine nine five kyozan joshu sasaki r shi one nine zero seven kodo sawaki one eight eight zero one nine six five taizan maezumi one nine three one one nine nine five soyen shaku r shi one eight five nine one nine one nine nyogen senzaki r shi one eight one nine five eight e |
ido shimano r shi shunryu suzuki r shi one nine zero four one nine seven one haku un yasutani r shi one eight eight five one nine seven three chinese ven hsing yun one nine two seven ven hsin ting one nine four four ven hsuan hua one nine one eight one nine nine five ven hsu yun one eight four zero one nine five nine ven sheng yen one nine three one american anne hopkins aitken one nine one one one nine nine four robert baker aitken r shi one nine one seven tenshin reb anderson zentatsu richard baker r shi john crook one nine three zero zoketsu norman fischer james ishmael ford r shi one nine four eight tetsugen bernard glassman r shi paul haller r shi cheri huber self declared teacher master hughes one nine five six self declared teacher philip kapleau r shi one nine one two two zero zero four jiyu kennett r shi one nine two four one nine nine six bodhin kjolhede r shi one nine four eight jakusho kwong r shi one nine three five john daido loori r shi kobutsu shindo malone r shi john tarrant roshi one nine fo |
ur nine brad warner sensei korean seung sahn soen sa one nine two seven two zero zero four samu sunim one nine four one vietnamese thich thien an one nine two six one nine eight zero thich nhat hanh one nine two six miscellaneous anagarika dharmapala one eight six four one nine three three the world s debt to buddha natalie goldberg daisaku ikeda ven ching kung one nine two seven ven cheng yen one nine three seven jan willis ven dr k sri dhammananda one nine one nine teachers of controversial buddhist or buddhist influenced groups shoko asahara one nine five five li hongzhi one nine five two lu sheng yen one nine four five sangharakshita one nine two five geshe kelsang gyatso one nine three one suma ching hai modern scholars and authors sir edwin arnold light of asia bhimrao ramji ambedkar one eight nine one one nine five six moni bagghee our buddha egerton c baptist supreme science of the buddha stephen batchelor susan blackmore niels bohr e a burtt the compassionate buddha thomas cleary edward conze one nin |
e zero four one nine seven nine buddhism albert einstein science princeton university may one nine th one nine three nine prof eliot buddhism and hinduism mark epstein thoughts without a thinker anatole france gertrude garartt charles t ghoram ven gnanatiloka daniel goleman destructive emotions george grimm the doctrine of the buddha von glasenapp nakamura hajime one nine one one one nine nine nine edmond holmes the creed of buddha graham howe christmas humphreys buddhism aldous leonard huxley w f jayasuriya the philosophy of buddism k n jayatilleke buddhism and peace rune johansson the psychology of nirvana carl g jung phra khantipalo tolerance nishida kitaro one eight seven zero one nine four five nishitani keiji one nine zero zero one nine nine zero count keyserling holger kersten the original jesus the buddhist sources of christianity ven narada maha thera what is buddhism ven a mahinda blue print of happines manhae one eight seven nine one nine four four abe masao born one nine one five geoffrey mortimer |
max muller lakhsmi narasu the essence of buddhism henry steel olcott one eight three two one nine zero seven oldenburg j robert oppenheimer karl pearson s radhakrisnan gautama the buddha walpola rahula bertrand russell why i am not a christian c a f rhys davids one eight five seven one nine four two t w rhys davids one eight four three one nine two two scott shaw gary snyder d t suzuki one eight seven zero one nine six six robert thurman albert schweitzer john walters mind unshaken h g wells the greatest men in history alfred north whitehead dudley wright ven yin shun the way to buddhahood one nine zero six two zero zero five marquess of zetland legecy of india modern politicians activists and protestors aung san suu kyi jerry brown tenzin delek rinpoche phoolan devi david emerson yohei kono norodom sihanouk norodom sihamouni sulak sivaraksa thaksin shinawatra u thant thich quang duc kwik kian gie indonesian former ministry celebrity buddhists asian jackie chan actor leslie cheung actor musician maggie cheun |
g actor tisca chopra actor model stephen chow comedy actor watazumi doso r shi shakuhachi flutist william hung singer american idol aaron kwok popstar actor andy lau popstar actor jet li martial artist actor anita mui pop singer actor teresa teng singer faye wong singer sally yeh popstar michelle yeoh actor dancer ken chu popstar f four band lee byung hun south korean actor jang dong gun south korean actor western adewale akinnuoye agbaje actor ernestine anderson jazz singer gillian anderson actor the x files season seven eps all things bleak house laurie anderson musician andrew black poker player orlando bloom actor kate bosworth actor ellen burstyn actor david carradine actor kung fu leonard cohen poet singer rob cohen film director producer writer mark copani actor pen lope cruz actor patrick duffy actor michael everson linguist harrison ford actor william clay ford jr ceo of ford richard gere actor allen ginsberg poet philip glass composer ron glass actor jake gyllenhaal actor herbie hancock musician kir |
k hammett musician goldie hawn actor frank herbert author bell hooks academic andy houts actor christmas humphreys judge scholar maxi jazz rapper charles johnson writer steve jobs founder ceo of apple computer jack kerouac writer poet jennifer lopez singer actor joanna lumley actor melissa mathison screenwriter kundun e t lisaraye mccoy actor gustav meyrink writer translator banker john milius screenwriter film director me shell ndegeocello singer musician kathleen dee anne norris actor model brad pitt actor seven years in tibet diane di prima poet keanu reeves actor little buddha bruce joel rubin screenwriter steven seagal actor martial artist lisa simpson cartoon character the simpsons she of little faith duncan sheik singer songwriter wayne shorter musician patti smith singer michael stipe singer oliver stone film director sharon stone see also list of scientologists uma thurman actor daughter of robert thurman tina turner singer what s love got to do with it gene vincent musician mark wahlberg model singe |
r actor alice walker writer naomi watts actor ruby wax comedy actor adam yauch rapper mca of the beastie boys brad wilk audioslave s drummer sport roberto baggio italian footballer fabien barthez french footballer edgar davids dutch footballer ivan de la pena spanish footballer milene domingues brazilian female footballer ex wife of ronaldo phil jackson basketball manager tiger woods golfer the people in this list have been included because they are or were agnostics that is they believe that the truth value of any claim regarding the existence of god gods or deities is unknown inherently unknowable or incoherent and they have themselves expressed it openly on the record or in their works personal correspondence diaries etc presumed agnostics are not included here given the different possible qualifications and uses through time of agnostic and other words relating to doubt unbelief or uncertainty about the existence of god or gods labels other than agnostic such as skeptic atheist or nontheist might also app |
ly to some of these people but the list attempts to be inclusive on this matter the reader should consult the relevant biographical articles for details the list includes agnostics who are or were notable defenders of agnosticism or who advocated views that could accurately be described as agnostic in short these people are or were important for other agnostics since they contribute d to the popularization understanding and acceptance of agnosticism in society either through their works or through their deeds the list also includes famous people who just happen happened to be agnostics and whose agnosticism is was relevant in their life but who do not did not actively advocate the position there might not be a consensus on whether a given person belongs on this list since obviously there is no way of listing all famous people who just happen to be agnostics there is no point either many of these profess their agnosticism as just a peripheral issue in their lives or simply keep quiet about it and they will not |
be listed here sir david attenborough one nine two six british natural history presenter and anthropologist helen clark new zealand prime minister clarence darrow one eight five seven one nine three eight american lawyer who defended john t scopes right to teach darwin s theory of evolution in the famous tennessee monkey trial charles darwin one eight zero nine one eight eight two founder of the theory of evolution by natural selection once described himself as being generally agnostic though he was a member of the anglican church and attended unitarian services mile durkheim one eight five eight one nine one seven french sociologist who had a jewish confirmation at thirteen was briefly interested in catholicism after a mystical experience but later became an agnostic heinz fischer b one nine three eight president of austria frederick james furnivall one eight two five one nine one zero second editor of the oxford english dictionary thomas henry huxley one eight two five one eight nine five coiner of the ter |
m agnosticism robert ingersoll one eight three three one eight nine nine american political leader and orator and known as the great agnostic said that it seems to me that the man who knows the limitations of the mind who gives the proper value to human testimony is necessarily an agnostic protagoras d four two zero bce greek sophist and first major humanist who wrote that the existence of the gods was unknowable andy rooney b one nine one nine broadcast personality who had specified that he was an agnostic and not an atheist but has also called himself an atheist bertrand russell one eight seven two one nine seven zero english philosopher and mathematician who considered himself a philosophical agnostic but said that the label atheist conveyed a more accurate impression to the ordinary man in the street carl sagan one nine three four one nine nine six astronomer and skeptic charles templeton one nine one five two zero zero one former evangelist author of a farewell to god mark twain has received many labels |
including agnostic and deist many quotations from twain suggest a sincere belief in a deity while expressing brutal skepticism and irreverence toward conventional religion s claims to know god s nature robert anton wilson b one nine three two author futurologist cryptocracy historian lee kuan yew singapore minister mentor see also list of atheists list of people by belief external links famous agnostics at the celebrity atheist list famous black freethinkers famous dead nontheists notes and references interview with simon mayo bbc radio five live two december two zero zero five do you believe in him now helen darwin wrote my judgment often fluctuates in my most extreme fluctuations i have never been an atheist in the sense of denying the existence of a god i think that generally and more and more as i grow older but not always that an agnostic would be the more correct description of my state of mind the life and letters of charles darwin ch viii p two seven four new york d appleton shortly after his traditio |
nal jewish confirmation at the age of thirteen durkheim under the influence of a catholic woman teacher had a shortlived mystical experience that led to an interest in catholicism but soon afterwards he turned away from all religious involvement though emphatically not from interest in religious phenomena and became an agnostic see ridener s page on famous dead sociologists see also coser s book masters of sociological thought ideas in historical and social context two nd ed fort worth harcourt brace jovanovich inc one nine seven seven one four three one four four furnivall was a deeply committed socialist and until his later agnosticism set in a somewhat enthusiastic christian simon winchester two zero zero three the meaning of everything the story of the oxford english dictionary oxford university press isbn zero one nine eight six zero seven zero two four why am i agnostic robert green ingersoll one eight eight nine see also ingersoll s complete works which includes many speeches and writings on religion a |
nd agnosticism only fragments of protagoras treatise on the gods survive but it opens with the sentence concerning the gods i have no means of knowing whether they exist or not or of what sort they may be many things prevent knowledge including the obscurity of the subject and the brevity of human life rooney wrote i call myself an agnostic not an atheist because in one sense atheists are like christians or muslims they re sure of themselves a christian says with certainty there is a god an atheist says with certainty there is no god neither knows sincerely andy rooney two zero zero one public affairs isbn one five eight six four eight zero four five six rooney said why am i an atheist i ask you why is anybody not an atheist everyone starts out being an atheist no one is born with belief in anything infants are atheists until they are indoctrinated i resent anyone pushing their religion on me i don t push my atheism on anybody else live and let live not many people practice that when it comes to religion mari |
an christy conversations we make our own destiny boston globe three zero may one nine eight two from newsbank rooney said i am an atheist i don t understand religion at all i m sure i ll offend a lot of people by saying this but i think it s all nonsense from a speech at tufts university one eight november two zero zero four russell said as a philosopher if i were speaking to a purely philosophic audience i should say that i ought to describe myself as an agnostic because i do not think that there is a conclusive argument by which one prove that there is not a god on the other hand if i am to convey the right impression to the ordinary man in the street i think i ought to say that i am an atheist none of us would seriously consider the possibility that all the gods of homer really exist and yet if you were to set to work to give a logical demonstration that zeus hera poseidon and the rest of them did not exist you would find it an awful job you could not get such proof therefore in regard to the olympic gods |
speaking to a purely philosophical audience i would say that i am an agnostic but speaking popularly i think that all of us would say in regard to those gods that we were atheists in regard to the christian god i should i think take exactly the same line am i an agnostic or an atheist from last philosophical testament one nine four three one nine six eight one nine nine seven routledge isbn zero four one five zero nine four zero nine seven russell was chosen by look magazine to speak for agnostics in their well known series explaining the religions of the u s and authored the essay what is an agnostic which appeared november three one nine five three in that magazine regarding carl sagan unbeliever s quest by jerry adler in newsweek march three one one nine nine seven in one of our walks about hartford when he was in the first fine flush of his agnosticism he declared that christianity had done nothing to improve morals and conditions dean howells my mark twain dean howells and mark twain had much in common t |
hey were agnostic but compassionate of the plight of man in an indifferent world darrel abel two zero zero two classic authors of the gilded age iuniverse isbn zero five nine five two three four nine seven six at the most mark twain was a mild agnostic usually he seems to have been an amused deist yet at this late date his own daughter has refused to allow his comments on religion to be published kenneth rexroth humor in a tough age the nation march seven one nine five nine e g to trust the god of the bible is to trust an irascible vindictive fierce and ever fickle and changeful master to trust the true god is to trust a being who has uttered no promises but whose beneficent exact and changeless ordering of the machinery of his colossal universe is proof that he is at least steadfast to his purposes mark twain a biography v i p four one two man even believes the creator loves him has a passion for him sits up nights to admire him yes and watch over him and keep him out of trouble he prays to him and thinks he |
listens isn t it a quaint idea mark twain letters from the earth p seven ed bernard devoto one nine six two harper and row library of congress catalog six two one four five five zero toward the end of his life he expressed anger toward god describing man as an april fool joke played by a malicious urchin creator and solipsistic nihilism there is nothing there is no god and no universe there is only empty space and in it a lost and homeless and wandering and companionless and indestructible thought agnostics in computer science a linked list is one of the fundamental data structures used in computer programming it consists of a sequence of nodes each containing arbitrary data fields and one or two references links pointing to the next and or previous nodes a linked list is a self referential datatype because it contains a pointer or link to another data of the same type linked lists permit insertion and removal of nodes at any point in the list in constant time but do not allow random access several different |
types of linked list exist singly linked lists doubly linked lists and circularly linked lists linked lists can be implemented in most languages languages such as lisp and scheme have the data structure built in along with operations to access the linked list procedural languages such as c c and java typically rely on mutable references to create linked lists history linked lists were developed in one nine five five five six by allen newell cliff shaw and herbert simon at rand corporation as the primary data structure for their information processing language ipl was used by the authors to develop several early artificial intelligence programs including the logic theory machine the general problem solver and a computer chess program reports on their work appeared in ire transactions on information theory in one nine five six and several conference proceedings from one nine five seven one nine five nine including proceedings of the western joint computer conference in one nine five seven and one nine five eig |
ht and information processing proceedings of the first unesco international conference on information processing in one nine five nine the now classic diagram consisting of blocks representing list nodes with arrows pointing to successive list nodes appears in programming the logic theory machine by newell and shaw in proc wjcc february one nine five seven newell and simon were recognized with the acm turing award in one nine seven five for having made basic contributions to artificial intelligence the psychology of human cognition and list processing the problem of machine translation for natural language processing led victor yngve at massachusetts institute of technology mit to use linked lists as data structures in his comit programming language for computer research in the field of linguistics a report on this language entitled a programming language for mechanical translation appeared in mechanical translation in one nine five eight lisp standing for list processor was created by john mccarthy in one ni |
ne five eight while he was at mit and in one nine six zero he published its design in a paper in the communications of the acm entitled recursive functions of symbolic expressions and their computation by machine part i one of lisp s major data structures is the linked list by the early one nine six zero s the utility of both linked lists and languages which use these structures as their primary data representation was well established bert green of the mit lincoln laboratory published a review article entitled computer languages for symbol manipulation in ire transactions on human factors in electronics in march one nine six one which summarized the advantages of the linked list approach a later review article a comparison of list processing computer languages by bobrow and raphael appeared in communications of the acm in april one nine six four several operating systems developed by technical systems consultants originally of west lafayette indiana and later of raleigh north carolina used singly linked list |
s as file structures a directory entry pointed to the first sector of a file and succeeding portions of the file were located by traversing pointers systems using this technique included flex for the motorola six eight zero zero cpu mini flex same cpu and flex nine for the motorola six eight zero nine cpu a variant developed by tsc for and marketed by smoke signal broadcasting in california used doubly linked lists in the same manner the tss operating system developed by ibm for the system three six zero three seven zero machines used a double linked list for their file system catalog the directory structure was similar to unix where a directory could contain files and or other directories and extend to any depth a utility flea was created to fix file system problems after a crash since modified portions of the file catalog were sometimes in memory when a crash occurred problems were detected by comparing the forward and backward links for consistency if a forward link was corrupt then if a backward link to t |
he infected node was found the forward link was set to the node with the backward link a humorous comment in the source code where this utility was invoked stated everyone knows a flea caller gets rid of bugs in cats variants linearly linked list singly linked list the simplest kind of linked list is a singly linked list or slist for short which has one link per node this link points to the next node in the list or to a null value or empty list if it is the final node image singly linked list png a singly linked list containing three integer values doubly linked list a more sophisticated kind of linked list is a doubly linked list or two way linked list each node has two links one points to the previous node or points to a null value or empty list if it is the first node and one points to the next or points to a null value or empty list if it is the final node image doublylinkedlist png an example of a doubly linked list in some very low level languages xor linking offers a way to implement doubly linked list |
s using a single word for both links although the use of this technique is usually discouraged circularly linked list in a circularly linked list the first and final nodes are linked together this can be done for both singly and doubly linked lists to traverse a circular linked list you begin at any node and follow the list in either direction until you return to the original node viewed another way circularly linked lists can be seen as having no beginning or end this type of list is most useful for managing buffers for data ingest and in cases where you have one object in a list and wish to see all other objects in the list the pointer pointing to the whole list is usually called the end pointer singly circularly linked list in a singly circularly linked list each node has one link similarly to an ordinary singly linked list except that the next link of the last node points back to the first node as in a singly linked list new nodes can only be efficiently inserted after a node we already have a reference t |
o for this reason it s usual to retain a reference to only the last element in a singly linked list as this allows quick insertion at the beginning and also allows access to the first node through the last node s next pointer doubly circularly linked list in a doubly circularly linked list each node has two links similarly to doubly linked list except that previous link of the first node points to the last node and the next link of the last node points to the first node as in a doubly linked lists insertions and removals can be done at any point with access to any nearby node sentinel nodes linked lists sometimes have a special dummy or sentinel node at the beginning and or at the end of the list which is not used to store data its purpose is to simplify or speed up some operations by ensuring that every data node always has a previous and or next node and that every list even one that contains no data elements always has a first and last node lisp has such a design the special value nil is used to mark the e |
nd of a proper singly linked list or chain of cons cells as they are called however a list does not have to end in nil but such a list would be termed improper applications of linked lists linked lists are used as a building block for many other data structures such as stacks queues and their variations the data field of a node can be another linked list by this device one can construct many linked data structures with lists this practice originated in the lisp programming language where linked lists are a primary though by no means the only data structure and is now a common feature of the functional programming style sometimes linked lists are used to implement associative arrays and are in this context called association lists there is very little good to be said about this use of linked lists they are easily outperformed by other data structures such as self balancing binary search trees even on small data sets see the discussion in associative array however sometimes a linked list is dynamically created |
out of a subset of nodes in such a tree and used to more efficiently traverse that set tradeoffs as with most choices in computer programming and design no method is well suited to all circumstances a linked list data structure might work well in one case but cause problems in another this is a list of some of the common tradeoffs involving linked list structures in general if you have a dynamic collection where elements are frequently being added and deleted and the location of new elements added to the list is significant then benefits of a linked list increase linked lists vs arrays linked lists have several advantages over arrays elements can be inserted into linked lists indefinitely while an array will eventually either fill up or need to be resized an expensive operation that may not even be possible if memory is fragmented similarly an array from which many elements are removed may become wastefully empty or need to be made smaller further memory savings can be achieved in certain cases by sharing the |
same tail of elements among two or more lists that is the lists end in the same sequence of elements in this way one can add new elements to the front of the list while keeping a reference to both the new and the old versions a simple example of a persistent data structure on the other hand arrays allow random access while linked lists allow only sequential access to elements singly linked lists in fact can only be traversed in one direction this makes linked lists unsuitable for applications where it s useful to look up an element by its index quickly such as heapsort sequential access on arrays is also faster than on linked lists on many machines due to locality of reference and data caches linked lists receive almost no benefit from the cache another disadvantage of linked lists is the extra storage needed for references which often makes them impractical for lists of small data items such as characters or boolean values it can also be slow and with a na ve allocator wasteful to allocate memory separately |
for each new element a problem generally solved using memory pools a number of linked list variants exist that aim to ameliorate some of the above problems unrolled linked lists store several elements in each list node increasing cache performance while decreasing memory overhead for references cdr coding does both these as well by replacing references with the actual data referenced which extends off the end of the referencing record a good example that highlights the pros and cons of using arrays vs linked lists is by implementing a program that resolves the josephus problem the josephus problem is an election method that works by having a group of people stand in a circle starting at a predetermined person you count around the circle n times once you reach n th person take them out of the circle and have the members close the circle then count around the circle the same n times and repeat the process until only one person is left that person wins the election this shows the strengths and weaknesses of a l |
inked list vs an array because if you view the people as connected nodes in a circular linked list then it shows how easily the linked list is able to delete nodes as it only has to rearrange the links to the different nodes however the linked list will be poor at finding the next person to remove and will need to recurse through the list till it finds that person an array on the other hand will be poor at deleting nodes or elements as it cannot remove one node without individually shifting all the elements up the list by one however it is exceptionally easy to find the n th person in the circle by directly referencing them by their position in the array doubly linked vs singly linked double linked lists require more space per node unless one uses xor linking and their elementary operations are more expensive but they are often easier to manipulate because they allow sequential access to the list in both directions in particular one can insert or delete a node in a constant number of operations given only tha |
t node s address some algorithms require access in both directions on the other hand they do not allow tail sharing and cannot be used as persistent data structures circularly linked vs linearly linked circular linked lists are most useful for describing naturally circular structures and have the advantage of regular structure and being able to traverse the list starting at any point they also allow quick access to the first and last records through a single pointer the address of the last element their main disadvantage is the complexity of iteration which has subtle special cases sentinel nodes sentinel nodes may simplify certain list operations by ensuring that the next and or previous nodes exist for every element however sentinel nodes use up extra space especially in applications that use many short lists and they may complicate other operations to avoid the extra space requirement the sentinel nodes can often be reused as references to the first and or last node of the list linked list operations when |
manipulating linked lists in place care must be taken to not use values that you have invalidated in previous assignments this makes algorithms for inserting or deleting linked list nodes somewhat subtle this section gives pseudocode for adding or removing nodes from singly doubly and circularly linked lists in place throughout we will use null to refer to an end of list marker or sentinel which may be implemented in a number of ways linearly linked lists singly linked lists our node data structure will have two fields we also keep a variable firstnode which always points to the first node in the list or is null for an empty list record node record list traversal of a singly linked list is easy beginning at the first node and following each next link until we come to the end node list firstnode while node not null the following code inserts a node after an existing node in a singly linked list the diagram shows how it works inserting a node before an existing one cannot be done instead you have to locate it w |
hile keeping track of the previous node center function insertafter node node node newnode inserting at the beginning of the list requires a separate function this requires updating firstnode function insertbeginning list list node newnode similarly we have functions for removing the node after a given node and for removing a node from the beginning of the list the diagram demonstrates the former to find and remove a particular node one must again keep track of the previous element center function removeafter node node function removebeginning list list node node notice that removebeginning sets list firstnode to null when removing the last node in the list since we can t iterate backwards efficient insertbefore or removebefore operations are not possible doubly linked lists with doubly linked lists there are even more pointers to update but also less information is needed since we can use backwards pointers to observe preceding elements in the list this enables new operations and eliminates special case func |
tions we will add a prev field to our nodes pointing to the previous element and a lastnode field to our list structure which always points to the last node in the list both list firstnode and list lastnode are null for an empty list record node record list iterating through a doubly linked list can be done in either direction in fact direction can change many times if desired forwards node list firstnode while node null node node next backwards node list lastnode while node null node node prev these symmetric functions add a node either after or before a given node with the diagram demonstrating after center function insertafter list list node node node newnode newnode prev node newnode next node next if node next null list lastnode newnode else node next prev newnode node next newnode function insertbefore list list node node node newnode newnode prev node prev newnode next node if node prev is null list firstnode newnode else node prev next newnode node prev newnode we also need a function to insert a node |
at the beginning of a possibly empty list function insertbeginning list list node newnode if list firstnode null list firstnode newnode list lastnode newnode newnode prev null newnode next null else insertbefore list list firstnode newnode a symmetric function inserts at the end function insertend list list node newnode if list lastnode null insertbeginning list newnode else insertafter list list lastnode newnode removing a node is easier only requiring care with the firstnode and lastnode function remove list list node node if node prev null list firstnode node next else node prev next node next if node next null list lastnode node prev else node next prev node prev destroy node one subtle consequence of this procedure is that deleting the last element of a list sets both firstnode and lastnode to null and so it handles removing the last node from a one element list correctly notice that we also don t need separate removebefore or removeafter methods because in a doubly linked list we can just use remove no |
de prev or remove node next where these are valid circularly linked lists circularly linked lists can be either singly or doubly linked in a circularly linked list all nodes are linked in a continuous circle without using null for lists with a front and a back such as a queue one stores a reference to the last node in the list the next node after the last node is the first node elements can be added to the back of the list and removed from the front in constant time both types of circularly linked lists benefit from the ability to traverse the full list beginning at any given node this often allows us to avoid storing firstnode and lastnode although if the list may be empty we need a special representation for the empty list such as a lastnode variable which points to some node in the list or is null if it s empty we use such a lastnode here this representation significantly simplifies adding and removing nodes with a non empty list but empty lists are then a special case doubly circularly linked lists assumi |
ng that somenode is some node in a non empty list this code iterates through that list starting with somenode any node will do forwards node somenode do do something with node value node node next while node somenode backwards node somenode do do something with node value node node prev while node somenode notice the postponing of the test to the end of the loop this is important for the case where the list contains only the single node somenode this simple function inserts a node into a doubly linked circularly linked list after a given element function insertafter node node node newnode newnode next node next newnode prev node node next prev newnode node next newnode to do an insertbefore we can simply insertafter node prev newnode inserting an element in a possibly empty list requires a special function function insertend list list node node if list lastnode null node prev node node next node else insertafter list lastnode node list lastnode node to insert at the beginning we simply insertafter list lastno |
de node finally removing a node must deal with the case where the list empties function remove list list node node if node next node list lastnode null else node next prev node prev node prev next node next if node list lastnode list lastnode node prev destroy node as in doubly linked lists removeafter and removebefore can be implemented with remove list node prev and remove list node next linked lists using arrays of nodes languages that do not support any type of reference can still create links by replacing pointers with array indices the approach is to keep an array of records where each record has integer fields indicating the index of the next and possibly previous node in the array not all nodes in the array need be used if records are not supported as well parallel arrays can often be used instead as an example consider the following linked list record that uses arrays instead of pointers record entry by creating an array of these structures and an integer variable to store the index of the first elem |
ent a linked list can be built integer listhead entry records one zero zero zero links between elements are formed by placing the array index of the next or previous cell into the next or prev field within a given element for example indexnextprevnamebalance zero one four jones john one two three four five one one zero smith joseph two three four five six two four one adams adam zero zero zero three ignore ignatius nine nine nine nine nine four zero two another anita eight seven six five four five six seven in the above example listhead would be set to two the location of the first entry in the list notice that entry three and five through seven are not part of the list these cells are available for any additions to the list by creating a listfree integer variable a free list could be created to keep track of what cells are available if all entries are in use the size of the array would have to be increased or some elements would have to be deleted before new entries could be stored in the list the following |
code would traverse the list and display names and account balance i listhead while i zero when faced with a choice the advantages of this approach include the linked list is relocatable meaning it can be moved about in memory at will and it can also be quickly and directly serialized for storage on disk or transfer over a network especially for a small list array indexes can occupy significantly less space than a full pointer on many architectures locality of reference can be improved by keeping the nodes together in memory and by periodically rearranging them although this can also be done in a general store na ve dynamic memory allocators can produce an excessive amount of overhead storage for each node allocated almost no allocation overhead is incurred per node in this approach seizing an entry from a pre allocated array is faster than using dynamic memory allocation for each node since dynamic memory allocation typically requires a search for a free memory block of the desired size this approach has one |
main disadvantage however it creates and manages a private memory space for its nodes not only does this increase complexity of the implementation but growing it may be difficult or impossible because it is large whereas finding space for a new linked list node in a large general memory pool is easier this slow growth also affects algorithmic performance as it causes a few insert operations to unexpectedly take linear o n instead of constant time although it s still amortized constant using a general memory pool also leaves more memory for other data if the list is smaller than expected or if many nodes are freed for these reasons this approach is mainly used for languages that do not support dynamic memory allocation these disadvantages are also mitigated if the maximum size of the list is known at the time the array is created language support many programming languages such as lisp and scheme have singly linked lists built in in many functional languages these lists are constructed from nodes each called |
a cons or cons cell the cons has two fields the car a reference to the data for that node and the cdr a reference to the next node although cons cells can be used to build other data structures this is their primary purpose in other languages linked list are typically built using references together with records here is a complete example in c include for printf include for malloc typedef struct ns node node list add node p int i void list remove node p node list search node n int i n return null void list print node n int main void internal and external storage when constructing a linked list one is faced with the choice of whether to store the data of the list directly in the linked list nodes called internal storage or to merely store a reference to the data called external storage internal storage has the advantage of making access to the data more efficient requiring less storage overall having better locality of reference and simplifying memory management for the list its data is allocated and deallocat |
ed at the same time as the list nodes external storage on the other hand has the advantage of being more generic in that the same data structure and machine code can be used for a linked list no matter what the size of the data is it also makes it easy to place the same data in multiple linked lists note however that even with internal storage the same data can be placed in multiple lists either by including multiple next references in the node data structure or by having other linked lists store references to the nodes of the linked list containing the data a common misconception is that every list using internal storage requires a new set of functions to operate on the linked list consuming more effort and code space than an approach using external storage this is true with a na ve approach but as long as the next pointers are located in the same place in each record it is possible to create a generic implementation of linked lists with internal storage that only needs to be supplied for each type of list a |
way of creating and destroying nodes example suppose you wanted to create a linked list of families and their members using internal storage the structure might look like the following record member record family to print a complete list of families and their members using internal storage we could write afamily families start at head of families list while afamily null afamily afamily next using external storage we would create the following structures record node record member record family to print a complete list of families and their members using external storage we could write famnode families start at head of families list while famnode null famnode famnode next notice that when using external storage an extra step is needed to extract the record from the node and cast it into the proper data type speeding up search finding a specific element in a linked list even if it is sorted normally requires o n time linear search this is one of the primary disadvantages of linked lists over other data structur |
es in addition to some of the variants discussed in the above section there are number of simple ways of improving search time in an unordered list one simple heuristic for decreasing average search time is the move to front heuristic which simply moves an element to the beginning of the list once it is found this scheme handy for creating simple caches ensures that the most recently used items are also the quickest to find again another common approach is to index a linked list using a more efficient external data structure for example one can build a red black tree or hash table whose elements are references to the linked list nodes multiple such indexes can be built on a single list the disadvantage is that these indexes may need to be updated each time a node is added or removed or at least before that index is used again related data structures the skip list is a linked list augmented with layers of pointers for quickly jumping over large numbers of elements and then descending to the next layer this pro |
cess continues down to the bottom layer which is the actual list a binary tree can be seen as a type of linked list where the elements are themselves linked lists of the same nature the result is that each node may include a reference to the first node of one or two other linked lists which together with their contents form the subtrees below that node an unrolled linked list is a linked list in which each node contains an array of data values this leads to improved cache performance since more list elements are contiguous in memory and reduced memory overhead because less metadata needs to be stored for each element of the list a hash table may use linked lists to store the chains of items that hash to the same position in the hash table references national institute of standards and technology august one six two zero zero four definition of a linked list retrieved december one four two zero zero four antonakos james l and mansfield kenneth c jr practical data structures using c c one nine nine nine prentice |
hall isbn zero one three two eight zero eight four three nine pp one six five one nine zero collins william j data structures and the java collections framework two zero zero two two zero zero five new york ny mcgraw hill isbn zero zero seven two eight two three seven nine eight pp two three nine three zero three cormen thomas h leiserson charles e rivest ronald l stein clifford introductions to algorithms two zero zero three mit press isbn zero two six two zero three two nine three seven pp two zero five two one three five zero one five zero five green bert f jr one nine six one computer languages for symbol manipulation ire transactions on human factors in electronics two pp three eight mccarthy john one nine six zero recursive functions of symbolic expressions and their computation by machine part i communications of the acm html dvi pdf postscript donald knuth fundamental algorithms third edition addison wesley one nine nine seven isbn zero two zero one eight nine six eight three four sections two two th |
ree two two five pp two five four two nine eight thomas h cormen charles e leiserson ronald l rivest and clifford stein introduction to algorithms second edition mit press and mcgraw hill two zero zero one isbn zero two six two zero three two nine three seven section one zero two linked lists pp two zero four two zero nine newell allen and shaw f c one nine five seven programming the logic theory machine proceedings of the western joint computer conference pp two three zero two four zero parlante nick two zero zero one linked list basics stanford university pdf sedgewick robert algorithms in c one nine nine eight addison wesley isbn zero two zero one three one four five two five pp nine zero one zero nine shaffer clifford a a practical introduction to data structures and algorithm analysis one nine nine eight nj prentice hall isbn zero one three six six zero nine one one two pp seven seven one zero two wilkes maurice vincent one nine six four an experiment with a self compiling compiler for a simple list proc |
essing language annual review in automatic programming four one published by pergamon press wilkes maurice vincent one nine six four lists and why they are useful proceeds of the acm national conference philadelphia one nine six four acm publication p six four page f one one also computer journal seven two seven eight one nine six five kulesh shanmugasundaram april four two zero zero five linux kernel linked list explained external links description from the dictionary of algorithms and data structures some linked list materials are available from the stanford university computer science department introduction to linked lists linked list problems citations from citeseer learning lists generic list container type for ansi c by jeff hay shared singly linked list implementations data structures a logic gate is an arrangement of controlled switches used to calculate operations using boolean logic in digital circuits they are primarily implemented electronically using diodes transistors but can also be constructe |
d using electromagnetic relays fluidics optical or even mechanical elements basic logic gates and mechanical equivalents while semiconductor electronic logic see later is preferred in most applications relays and switches are still used in some industrial applications and for educational purposes in this article the various types of logic gates are illustrated with drawings of their relay and switch implementations although the reader should remember that these are electrically different from the semiconductor equivalents that are discussed later relay logic was historically important in industrial automation see ladder logic and programmable logic controller since relay contacts conduct in both directions complex logic designs must be checked for sneak paths that produce unintended logic paths semiconductor logic gates are not conductive in both directions as the input signal acts as a trigger to allow current out of the output rather than allowing current straight through from input to output however the fo |
llowing mechanical variations do show the basic principles of the gates without detailing the precise internal workings for information about how modern semiconductors really work see cmos the three types of essential logic gate are the and the or and the not gate with these three any conceivable boolean equation can be implemented however for convenience the derived types nand nor xor and xnor are also used which often use fewer circuit elements for a given equation than an implementation based solely on and or and not would do in fact the nand has the lowest component count of any gate apart from not when implemented using modern semiconductor techniques and since a nand can implement both a not and by application of de morgan s law an or function this single type can effectively replace and or and not making it the only type of gate that is needed in a real system programmable logic arrays will very often contain nothing but nand gates to simplify their internal design and gates the first example is the an |
d gate whose truth table is shown below left the boolean and function can be implemented with two switches a and b as shown below right if a power lead is connected to switch a and a wire connects switches a and b then both a and b have to be on in order for the output of the circuit to conduct electricity and provide power input output a b a and b zero zero zero one zero zero zero one zero one one one switch circuit diagram for and gate or gates another important arrangement is the or gate whose truth table is shown below left an or gate can be constructed from two switches arranged so that if either switch is on the output will also be on note that the output will still be on even if both switches are on input output a b a or b zero zero zero one zero one zero one one one one one switch circuit diagram for or gate not gates a simpler arrangement is the not gate whose truth table is shown opposite this is a special switch that when pushed breaks the current when it is pressed the normally closed contact of a |
relay can be used for this purpose input output a not a zero one one zero switch circuit diagram for not gate nand and nor gates using not gates also called inverters allows us to make alternate versions of the and and or gates by virtue of de morgan s law note that the layout of the switches in the two circuits is swapped when we turn the switches backwards also note how the output of the first pair controls the operation of the not gate switch diagram of alternate and and or gates this may seem like an unnecessary complication but in fact this is very useful by removing the not gate from these alternate circuits we create the so called nand for not and and nor for not or gates this is also important because transistors acting as switches are by thier nature inverting devices nand input output a b a nand b zero zero one one zero one zero one one one one zero switch circuit diagram of nand gate nor input output a b a nor b zero zero one one zero zero zero one zero one one zero switch circuit diagram of nor g |
ate xor and xnor gates there exist two other basic logic gates xor exclusive or and xnor exclusive nor input output a b a xor b zero zero zero zero one one one zero one one one zero xor is a stricter version of the or gate rather than allowing the output to be high when either one or both of the inputs are high an xor gate has a high output only when only one input is high as such it has the truth table shown to the right this can also be interpreted for a two input gate as high output when the inputs are different input output a b a xnor b zero zero one one zero zero zero one zero one one one xnor is an inverted version of the xor gate as such it has the truth table shown to the right this can also be interpreted as high output when the inputs are same the preceding simple logic gates can be combined to form more complicated boolean logic circuits logic circuits are often classified in two groups combinatorial logic in which the outputs are continuous time functions of the inputs and sequential logic in whic |
h the outputs depend on information stored by the circuits as well as on the inputs background the simplest form of electronic logic is diode logic this allows and and or gates to be built but not inverters and so is an incomplete form of logic to build a complete logic system valves or transistors can be used the simplest family of logic gates using bipolar transistors is called resistor transistor logic or rtl unlike diode logic gates rtl gates can be cascaded indefinitely to produce more complex logic functions these gates were used in early integrated circuits for higher speed the resistors used in rtl were replaced by diodes leading to diode transistor logic or dtl it was then discovered that one transistor could do the job of two diodes in the space of one diode so transistor transistor logic or ttl was created in some types of chip to reduce size and power consumption still further the bipolar transistors were replaced with complementary field effect transistors mosfets resulting in complementary metal |
oxide semiconductor cmos logic for small scale logic designers now use prefabricated logic gates from families of devices such as the ttl seven four zero zero series invented by texas instruments and the cmos four zero zero zero series invented by rca and their more recent descendants these devices usually contain transistors with multiple emitters used to implement the and function which are not available as separate components increasingly these fixed function logic gates are being replaced by programmable logic devices which allow designers to pack a huge number of mixed logic gates into a single integrated circuit the field programmable nature of programmable logic devices such as fpgas has removed the hard property of hardware it is now possible to change the logic design of a hardware system by reprogramming some of its components thus allowing the features or function of a hardware implementation of a logic system to be changed electronic logic gates differ significantly from their relay and switch eq |
uivalents they are much faster consume much less power and are much smaller all by a factor of a million or more in most cases also there is a fundamental structural difference the switch circuit creates a continuous metallic path for current to flow in either direction between its input and its output the semiconductor logic gate on the other hand acts as a high gain voltage amplifier which sinks a tiny current at its input and produces a low impedance voltage at its output it is not possible for current to flow between the output and the input of a semiconductor logic gate another important advantage of standardised semiconductor logic gates such as the seven four zero zero and four zero zero zero families is that they are cascadable this means that the output of one gate can be wired to the inputs of one or several other gates and so on ad infinitum enabling the construction of circuits of arbitrary complexity without requiring the designer to understand the internal workings of the gates in practice the o |
utput of one gate can only drive a finite number of inputs to other gates a number called the fanout limit but this limit is rarely reached in the newer cmos logic circuits as compared to ttl circuits also there is always a delay called the propagation delay from a change in input of a gate to the corresponding change in its output when gates are cascaded the total propagation delay is approximately the sum of the individual delays an effect which can become a problem in high speed circuits logic levels the two logic levels in binary logic circuits can be described as two voltage ranges zero and one or high and low each technology has its own requirements for the voltages used to represent the two logic levels to ensure that the output of any device can reliably drive the input of the next device usually two non overlapping voltage ranges one for each level are defined the difference between the high and low levels ranges from zero seven volts in ecl logic to around two eight volts in relay logic logic gates |
and hardware nand and nor logic gates are the two pillars of logic in that all other types of boolean logic gates i e and or not xor xnor can be created from a suitable network of just nand or just nor gate s they can be built from relays or transistors or any other technology that can create an inverter and a two input and or or gate these functions can be seen in the table below as you look at this table start with the name of a gate and read across the table while you apply the following statement basic logic functions or any high in will create a high output nor any high in will create a low output and any low in will create a low output nand any low in will create a high output logic gates are a vital part of many digital circuits and as such every kind is available as an ic for examples see the four zero zero zero series of cmos logic chips symbols there are two sets of symbols in common use both now defined by ansi ieee std nine one one nine eight four and its supplement ansi ieee std nine one a one ni |
ne nine one the distinctive shape set based on traditional schematics is used for simple drawings and is quicker to draw by hand it is sometimes unofficially described as military reflecting its origin if not its modern usage the rectangular shape set based on iec six zero six one seven one two has rectangular outlines for all types of gate and allows representation of a much wider range of devices than is possible with the traditional symbols the iec s system has been adopted by other standards such as en six zero six one seven one two one nine nine nine in europe and bs en six zero six one seven one two one nine nine nine in the united kingdom the seven four zero zero chip containing four nand s the two additional contacts supply power five v and connect the ground demorgan equivalent symbols by use of de morgan s theorem an and gate can be turned into an or gate by inverting the sense of the logic at its inputs and outputs this leads to a separate set of symbols with inverted inputs and the opposite core s |
ymbol these symbols can make circuit diagrams for circuits using active low signals much clearer and help to show accidental connection of an active high output to an active low input or vice versa storage of bits related to the concept of logic gates and also built from them is the idea of storing a bit of information the gates discussed up to here cannot store a value when the inputs change the outputs immediately react it is possible to make a storage element either through a capacitor which stores charge due to its physical properties or by feedback connecting the output of a gate to the input causes it to be put through the logic again and choosing the feedback correctly allows it to be preserved or modified through the use of other inputs a set of gates arranged in this fashion is known as a latch and more complicated designs that utilise clocks signals that oscillate with a known period and change only on the rising edge are called edge triggered flip flops the combination of multiple flip flops in par |
allel to store a multiple bit value is known as a register these registers or capacitor based circuits are known as computer memory they vary in performance based on factors of speed complexity and reliability of storage and many different types of designs are used based on the application three state logic gates three state or three state logic gates have three states of the output high h low l and high impedance z the high impedance state plays no role in the logic which remains strictly binary these devices are used on buses to allow multiple chips to send data a group of tristates driving a line with a suitable control cuircuit is basically equivilent to a multiplexer which may be physically distributed over separate devices or plug in cards tri state a widely used synonym of three state is a trademark of the national semiconductor corporation miscellaneous logic circuits include such devices as multiplexers registers alus and computer memory all the way up through complete microprocessors which can conta |
in more than a million gates in practice the gates are made from field effect transistors fets particularly metal oxide semiconductor fets mosfets in reversible logic toffoli gates are used history and development the earliest logic gates were made mechanically charles babbage around one eight three seven devised the analytical engine his logic gates relied on mechanical gearing to perform operations electromagnetic relays were later used for logic gates in one eight nine one almon strowger patented a device containing a logic gate switch circuit strowger s patent was not in widespread use until the one nine two zero s starting in one eight nine eight nikola tesla filed for patents of devices containing logic gate circuits see list of tesla patents eventually vacuum tubes replaced relays for logic operations lee de forest s modification in one nine zero seven of the fleming valve can be used as and logic gate claude e shannon introduced the use of boolean algebra in the analysis and design of switching circui |
ts in one nine three seven walther bothe inventor of the coincidence circuit got part of the one nine five four nobel prize in physics for the first modern electronic and gate in one nine two four common basic logic ics four zero zero one quad two input nor gate four zero one one quad two input nand gate four zero four nine hex not gate inverting buffer four zero seven zero quad two input xor gate four zero seven one quad two input or gate four zero seven seven quad two input xnor gate four zero eight one quad two input and gate for more cmos logic ics including gates with more than two inputs see four zero zero zero series see also digital circuit fanout karnaugh map list of boolean algebra topics families of logic devices nmos race hazard venn diagram external links and references symbols for logic gates twenty first century books breckenridge co tesla s invention of the and logic gate twenty first century books breckenridge co wireless remote control and the electronic computer logic gate twenty first cent |
ury books breckenridge co anderson leland i nikola tesla guided weapons isbn zero nine six three six zero one two five three bigelow ken how logic gates work internally for several logic families play hookey com c e shannon a symbolic analysis of relay and switching circuits transactions american institute of electrical engineers vol five seven pp seven one three seven two three march one nine three eight the iec symbols are defined in iec six zero six one seven one two one nine nine seven one two graphical symbols for diagrams part one two binary logic elements lego logic gates goldfish org uk two zero zero five further reading bostock geoff programmable logic devices technology and applications new york mcgraw hill c one nine eight eight isbn zero zero seven zero zero six six one one six brown stephen d et al field programmable gate arrays boston kluwer academic publishers c one nine nine two the kluwer international series in engineering and computer science isbn zero seven nine two three nine two four eig |
ht five awschalom d d loss and n samarth semiconductor spintronics and quantum computation berlin springer c two zero zero two isbn three five four zero four two one seven six nine digital electronics in computer science linear search is a search algorithm also known as sequential search that is suitable for searching a set of data for a particular value it operates by checking every element of a list until a match is found linear search runs in o n if the data are distributed randomly on average n two comparisons will be needed the best case is that the value is equal to the first element tested in which case only one comparison is needed the worst case is that the value is not in the list in which case n comparisons are needed the list module in the ocaml standard library defines a function called mem that returns true if the given element is in the given list or false if not this function could be defined as let rec mem x function false h t h x mem x t mathematica s unusually powerful pattern matching allo |
ws linear search to be implemented by a pattern match memx true mem false for implementations in real programming languages see linear search can be used to search an unordered list the more efficient binary search can only be used to search an ordered list if more than a small number of searches are needed it is advisable to use a more efficient data structure one approach is to sort and then use binary searches another common one is to build up a hash table and then do hash lookups references donald knuth the art of computer programming volume three sorting and searching third edition addison wesley one nine nine seven isbn zero two zero one eight nine six eight five zero section six one sequential searching pp three nine six four zero eight algorithms search algorithms various anti tank and anti personnel land mines a landmine is a type of self contained explosive device which is placed onto or into the ground exploding when triggered by a vehicle or person the name originates from the practice of sapping |
where tunnels were dug under opposing forces or fortifications and filled with explosives landmines generally refer to devices specifically manufactured for purpose as distinguished from improvised explosive devices landmines sometimes called area denial munitions are used to secure disputed borders and to restrict enemy movement in times of war tactically they serve a purpose similar to barbed wire or concrete dragon s teeth vehicle barriers channelling the movement of attacking troops in ways that permit the defenders to engage them more easily from a military perspective landmines serve as force multipliers allowing an organised force to overcome a larger enemy anti personnel landmines or apls are widely considered to be ethically problematic weapons because their victims are commonly civilians who are often killed or maimed long after a war has ended according to anti landmine campaigners in cambodia alone mines have resulted in three five zero zero zero amputees after the cessation of hostilities removal |
of landmines is dangerous slow and costly however some countries maintain that landmines are necessary to protect their soldiers in times of war history the basic concept behind the landmine has appeared through military history some sources report that zhuge liang of the kingdom of shu of china invented a landmine type device in the third century forces in ancient rome sometimes dug small foot sized holes covered and armed with a sharpened spike in the middle ages in europe small four pronged spiked devices called caltrops or crows feet could be scattered on the ground to delay the advance of an enemy in europe in the early eighteenth century improvised landmines or booby traps were constructed in the form of bombs buried in shallow wells in the earth and covered with scrap metal and or gravel to serve as shrapnel known in french as fougasse the term is sometimes still used in the present day to describe such devices this technique was used in several european wars of the eighteenth century the american rev |
olution and the american civil war the first modern mechanically fused high explosive anti personnel landmines were created in imperial germany circa one nine one two and were copied and manufactured by all major participants in the first world war in world war one landmines were used notably at the start of the battle of passchendale well before the war was over the british were manufacturing landmines that contained poison gas instead of explosives poison gas mines were manufactured at least until the one nine eight zero s in the soviet union the united states was known to have at least experimented with the concept in the one nine five zero s nuclear mines have also been developed both land and naval varieties an example is the british blue peacock project while another was the u s medium atomic demolition munition characteristics and functioning mine components a land mine typically includes the following components firing mechanism or other device including anti handling devices detonator or ignitor sets |
off the booster charge booster charge may be attached to the fuse or the ignitor or be part of the main charge main charge in a container usually forms the body of the mine casing contains all of the above parts firing mechanisms landmines made mostly of plastic have the added advantage of being very inexpensive some types of mines used by the u s army and many other forces are designed to self destruct after a period of weeks or months to reduce the likelihood of civilian casualties at the conflict s end however these self destruct mechanisms are not absolutely reliable and most landmines laid historically are not equipped in this manner anti handling devices ahd anti handling devices trigger the mine fuze if someone attempts to tamper or defuse the mine they are intended to prevent moving or removing the mine not to prevent reduction of the minefield by enemy dismounts an ahd usually consists of an explosive charge that is connected to placed next to or manufactured in the mine the device can be attached t |
o the mine body and activated by a wire that is attached to a firing mechanism u s forces employ ahds on conventional at mines only and not on anti personal mines the makes it somewhat safer to remove mines laid by us forces other countries may employ ahds on both at and ap mines landmine varieties anti tank mines at anti tank mines are designed to immobilise or destroy vehicles and their occupants anti tank mines can achieve either a mobility kill m kill or a catastrophic kill k kill a mobility kill destroys one or more of the vehicle s vital drive components for example breaking a track on a tank thus immobilising the target a mobility kill does not always destroy the weapon system or injure the crew in a catastrophic kill the weapon system and or the crew are disabled anti tank mines are typically larger than anti personnel mines and require more pressure to detonate the high trigger pressure normally one zero zero kg two two zero lb prevents them from being set off by infantry more modern anti tank mines |
use shaped charges to cut through armour these were first deployed in large numbers in world war ii anti personnel mines ap ap bounding mines anti personnel mines are designed to kill or incapacitate their victims such mines require the commitment of medical resources on the part of the affected enemy force may degrade unit morale and can damage unarmoured vehicles some types of ap mines may break or damage the track on armoured vehicles ap mines can be classified into three main types blast mines ap fragmentation mines and ap bounding mines ap blast mines a typical ap blast mine can be classified as pressure activated munition the primary purpose of which is to incapacitate via the direct blast wave of the explosive charge a typical ap blast mine will have the following components typical components of an ap blast mine mine casing the mine casing houses the components of the mine and protects it from its environment early landmines such as the ones found in the wwii era had casings made of steel and could be |
found with an electronic mine detector today most ap blast mines have a casing made out of plastic which makes them immune from electronic mine detectors pressure plate detonation mechanism the detonation mechanism is designed to set off the detonation charge either by striking it with a firing pin or passing an electric charge through it most ap blast mines use a spring loaded detonation mechanism that strikes the detonator charge when activated detonator the detonator charge is a highly sensitive explosive that will explode easily if sudden pressure is applied to it or an electric charge is applied through it main charge the main charge of an ap blast mine consists of stable explosive that is itself detonated by the detonator charge this is necessary as making a mine out of highly sensitive detonator charge explosive would make it dangerously susceptible to explosion in most ap blast mines tnt or tetryl is used on a u s m one four ap blast mine around three one grams of tetryl is used while up to two zero |
zero grams of tnt is used in a russian pmn mine deployment of ap blast mines ap blast mines are typically used to deny an area for use by military forces or civilians they are normally buried under five to one zero cm of soil or in some cases put under leaves or rocks consequences of activating an ap blast mine when a subject activates an ap blast mine by stepping on one the mine s main charge will explode and release a blast wave consisting of hot gases the by product of the explosion this blast wave will send a huge compressive force upwards bringing the mine casing and bits of the soil covering the mine along with it when the blast wave hits the surface it will quickly transfer the force into the subject s footwear and foot this results in a massive compression force being applied to the subject s footwear and the foot s soft tissue and bone in most cases these will be crushed and torn off by the blast wave the resulting injuries to a human body depend on the size of the blast mine s main charge the depth |
and type of soil it was laid in and how the victim contacted it different types of soil will result in different amounts of energy being transferred upward into the subject s extremities with saturated clay like soil transferring the most larger main charges result in a release of significantly more energy driving the blast wave further up a target s foot and leg and causing greater injury small landmines such as the chinese type seven two or the u s m one four will result in a traumatically amputated foot up to the ankle while large russian pmn blast mines with two zero zero g of tnt are so powerful that activating them will likely result in the injury of both of the subject s legs secondary injuries from a blast mine will be caused by the material that has been torn loose by the mine s explosion the material consists of the soil and stones that were on top of the mine parts of the subject s footwear and the small bones in the subject s foot this debris is projected upwards at great velocity and can become e |
mbedded in the wounds of the target shredding tissue and encouraging infection footwear including combat boots or so called blast boots does little to mitigate the effects of the mine and the loss of a foot is the typical outcome of activating an ap blast anti personnel fragmentation mines ap fragmentation mines such as the german s mine are a type of area denial munition designed to incapacitate or kill when activated the mine is designed to explode and project lethal metal fragments into its victim most ap fragmentation mines are triggered by a tripwire when a subject disturbs the wire the mine will explode and release a shower of metal fragments into its surroundings any subject caught in its blast will likely suffer multiple shrapnel wounds over his or her body mine warfare u s army soldier removes fuze from a russian made mine to clear a minefield outside of fallujah iraq in military science minefields are considered a defensive or harassing weapon used to slow the enemy down to help deny certain terrain |
to the enemy to focus enemy movement into kill zones or to reduce morale by randomly attacking mat riel and personnel since combat engineers with mine clearing equipment can clear a path through a minefield relatively quickly mines are usually considered effective only if covered by fire the extents of minefields are often marked with warning signs and cloth tape to prevent friendly troops and non combatants from entering them of course sometimes terrain can be denied using dummy minefields most forces carefully record the location and disposition of their own minefields because warning signs can be destroyed or removed and minefields should eventually be cleared minefields may also have marked or unmarked safe routes to allow friendly movement through them placing minefields without marking and recording them for later removal is considered uncivilized and is illegal under international conventions laying mines minefields may be laid by several means the preferred but most labour intensive way is to have en |
gineers bury the mines since this will make the mines practically invisible and reduce the number of mines needed to deny the enemy an area mines can be laid by specialized mine laying vehicles mine scattering shells may be fired by artillery from a distance of several tens of kilometres mines may be dropped from helicopters or airplanes or ejected from cruise missiles anti tank minefields can be scattered with anti personnel mines to make clearing them manually more time consuming and anti personnel minefields are scattered with anti tank mines to prevent the use of armoured vehicles to clear them quickly some anti tank mine types are also able to be triggered by infantry giving them a dual purpose even though their main and official intention is to work as anti tank weapons some minefields are specifically booby trapped to make clearing them more dangerous mixed anti personnel and anti tank minefields double stacked anti tank mines anti personnel mines under anti tank mines and fuzes separated from mines ha |
ve all been used for this purpose detecting and removing landmines hydrema mine clearing vehicle while placing and arming landmines is relatively inexpensive and simple the reverse of detecting and removing them is typically expensive slow and dangerous various means to detect landmines include carefully searching suspected or known minefields areas for mines often this is done by crawling slowly into the field inserting a probe anything from a knife to a stick into the soil to find hard objects when walking in mined areas mine clearing personnel may wear large pillow like pads strapped under their feet to spread their weight and dull the impact of their footsteps as very slight disturbances of the ground can tip off old unstable or intentionally sensitive mine triggers protective clothing protective demining shoes using metal detectors to sweep a suspected minefield however the detectors may not easily differentiate various types of metal objects which slows the search using animals like dogs that can sniff |
out explosive chemicals like tnt in landmines recent experiments with the gambian giant pouched rat have indicated that it has the required sensitivity to smell can be trained reliably with food reward incentives and is typically too small to set off the mines sowing genetically engineered flower seeds over suspected minefields from the air the flowers bloom in distinctive colours when there are explosives nearby in the soil methods for removing landmines include manually disarming them destroying or detonating them safely possibly using another explosive or even an artillery barrage driving a heavily armoured vehicle like an armoured bulldozer or a tank equipped with a mine roller plough or flail through a minefield to deliberately detonate the explosives using a specialized mine clearing explosive typically a pipe or hose filled with explosive material pushed or launched across a minefield examples include the bangalore torpedo giant viper and antipersonnel obstacle breaching system efforts to ban anti pers |
onnel mines after a sustained and successful international campaign led by a coalition of ngos and with key support from the government of canada the majority of the world s countries one four four to date have made the use and possession of anti personnel landmines by its military forces illegal the only three western democracies that have not banned anti personnel landmines are the united states finland and israel some other countries like russia china and north korea also continue to use and manufacture them the ottawa treaty convention on the prohibition of the use stockpiling production and transfer of anti personnel mines and on their destruction came into force on march one one nine nine nine the treaty was the result of the international campaign to ban landmines launched in one nine nine two the campaign and its leader jody williams won the nobel peace prize in one nine nine seven for its efforts signatories of the ottawa treaty agree that they will not use develop manufacture stockpile or trade in a |
nti personnel landmines existing stocks must be destroyed within four years of signing the treaty there were originally one two two signatories in one nine nine seven as of february two zero zero four it has been signed by one five two countries and ratified by one four four the remaining four two countries have not signed the biggest of these are the people s republic of china india the usa and the russian federation the united states refuses to sign the treaty because it does not offer a korean exception as landmines are a crucial component of the u s military strategy in south korea according to the us government the one million mines along the dmz between north and south help maintain the delicate peace by deterring a north korean attack despite conducting research on technologies that could replace the mines in korea by two zero zero six in one nine nine nine the u s modified the ottawa treaty by introducing the m eight six pursuit deterrent munition pdm which was meant to slow enemy pursuit on retreatin |
g armed forces while still a landmine pdm exploits technical loopholes in the ottawa treaty therefore the future of landmines in the u s is unclear according to the icbl report for august two zero zero four eighty countries declared stockpiles totalling four eight million landmines of which three seven five million have been destroyed so far six five countries have completed the destruction of their stockpiles and another five one countries have declared that they did not possess stockpiles to destroy nine countries signed the treaty in the year to august two zero zero four there is a clause in the treaty article three which permits countries to retain landmines for use in training or development of countermeasures six four countries have taken this option in february two zero zero four the number of mines retained varied from nine three for mauritius one seven eight three for the united kingdom around four zero zero zero for france and spain nine zero zero zero for japan right up to as many as six nine two z |
ero zero for turkmenistan other high levels are reported by brazil one six five four five sweden one six zero one five algeria one five zero three zero and bangladesh one five zero zero zero in total two eight nine zero zero zero mines have been declared as retained by various countries under article three a further two three countries have not declared a figure as an alternative to an outright ban one zero countries follow regulations that are contained in a one nine nine six amendment of protocol ii of the convention on conventional weapons ccw the countries are china finland india israel latvia morocco pakistan south korea sri lanka and the united states the ottawa treaty does not include anti tank mines cluster bombs or claymore type mines operated in command mode but does cover victim activated claymore type mines including those activated by tripwires manufacturers the icbl has identified the following countries as manufacturing landmines as of august two zero zero four none are signatories of the ottaw |
a treaty cuba iraq although production had presumably ceased since the invasion of two zero zero three iran india myanmar nepal north korea pakistan russian federation singapore vietnam of other states which are thought to have manufactured landmines recently turkey is now a signatory of the ottawa treaty serbia and montenegro is now a signatory of the ottawa treaty egypt has unofficially stated that production ceased in one nine eight eight the united states has not manufactured anti personnel mines since one nine nine seven but a government statement in february two zero zero four stated that the united states will continue to develop non persistent anti personnel and anti tank landmines south korea has stated that no mines have been produced since two zero zero zero an official from china stated in september two zero zero three that production has ceased there since they have an ample stockpile in march two zero zero four a libyan official stated that the country has never produced anti personnel mines but |
is known to have laid landmines in the one nine seven zero s and one nine eight zero s a united nations assessment mission to peru reported that production of landmines in the country ceased in january one nine nine nine peru was one of the original signatories and to the treaty came into force for them in march one nine nine nine the soviet union had been accused of using specifically designed mines looking like toys to target children in its conflict with afghanistan some of the soviet mines used were small green made from plastic and winged so that they could be deployed from planes with the result that children often mistook them for toys but others were allegedly manufactured of red and white plastic in the shape of toy trucks see also demining improvised explosive device cluster bomb naval mine anti mine organizations roots of peace international campaign to ban landmines icbl icbl landmine monitor http www icbl org lm types of mines and mine delivery systems used by us military artillery delivered ant |
ipersonnel mine adam m one four mine m one six mine claymore mine gator mine volcano mine ground emplaced mine scattering system gemss m eight six pursuit deterrent munition pdm modular pack mine system mopms controversy articles land mine controversy of afghanistan external links the international committee of the red cross on landmines the international campaign to ban landmines steve mcclure japan times one six may two zero zero one the sweet sound of a good cause zero landmine charity cd and television programme uk author alexander deane defends the use and legality of landmines aurora land mines task force an example of student activism against land mines demining with africa s sniffer rats apopo unicef s most heavily mined countries one nine nine five swiss foundation for mine action fsd the cambodia land mine museum landmines area denial weapons libertarian party can refer to several libertarian political parties including united states libertarian party libertarian party of canada movimiento libertari |
o of costa rica the libertarianz of new zealand libertarian party of australia libertarian party of netherlands there are also political parties that hold some of the same policies as the above parties but do not use the label libertarian freedom party of canada freedom party u s a personal choice party of the united states independence party of minnesota moderate libertarian liberal democratic party of australia free democratic party of germany free democratic party of switzerland civil resistance resistencia civil of venezuela act new zealand italian radicals radicali italiani of italy freedom union democratic union unie svobody demokratick unie of the czech republic estonian reform party eesti reformierakond of estonia liberal party hong kong libertarian in many aspects latvian way latvijas ce det liberale folkepartiet of norway liberala partiet of sweden unia polityki realnej real politics union of poland see also index of political parties to browse parties by name list of political parties to browse par |
ties by country list of political parties by ideology to browse parties by ideology membership of internationals to browse parties by membership of internationals lists of political parties by generic name libertarianism libertarian parties the loa also lwa or l wha are the spirits of the vodoun religion practiced in haiti and other parts of the world they are also referred to as the myst res and the invisibles they are somewhat akin to saints or angels in western religions in that they are intermediaries between bondye bon dieu or good god the creator who is distant from the world and humanity unlike saints or angels however they are not simply prayed to they are served also unlike other western gods they are not easily categorised into archetypal forms they are each distinct beings with their own personal likes and dislikes distinct sacred rythmns songs dances ritual symbols and special modes of service contrary to popular belief the loa are not deities they are intermediaries for a distant and uninterested |
bondye as a way to keep their european masters from interfering and to appease the authorities who prevented them from practising their own religions the african slaves in haiti syncretised the loa with the catholic saints so vodoun altars will frequently have images of catholic figures displayed for example papa legba is alternately st peter or st lazarus ayizan is st clair etc in a ritual the loa are summoned by the houngan priest or mambo priestess to take part in the service receive offerings and grant requests they arrive in the peristyle ritual space by taking possession mounting of a ritualist horse who is said to be ridden this can be quite a violent occurrence as the participant can flail about or convulse before falling to the ground but some loa will mount their horses very quietly ayizan is one such loa who usually never appears before her husband loco as soon as a loa is recognised the symbols appropriate to them will be given to them for example erzulie freda will be given a mirror and a comb f |
ine cloth or jewellery legba will be given his cane straw hat and pipe baron samedi will be given his top hat sunglasses and a cigar there are three main families or nations of loa rada also radha petro also pethro petwo and ghede also guede or gede the rada loa are generally the older more beneficent spirits they include legba loko ayizan dhamballah wedo and ayida wedo erzulie freda la sirene and agoueh their traditional colour is white as opposed to the specific colours of individual loa the petro loa are generally the more fiery occasionally agressive and warlike loa they include erzulie dantor marinette ogoun and kalfou carrefour their traditional colour is red the ghede are the spirits of the dead they are traditionally led by the barons la croix samedi cimitiere kriminel and maman brigitte the ghede as a family are loud rude although never insulting sexual and usually a lot of fun as those who have lived already they have nothing to fear and frequently will display how past consequence and feeling they |
are when they come through in a service eating glass raw chillis and annointing their sensitive areas with chilli rum for example their traditional colours are black and purple some loa adjassou linguetor adjinakou adya houn t agassou agwe ayida weddo ayizan azaka tonnerre bacalou badessy baron samedi boli shah bossou ashadeh boum ba maza bugid y aiba captain debas clermeil congo voodoo damballa dan petro dan w do diable tonnere diejuste dinclinsin erzulie ghede gran ma tre grand bois guinee kalfu lemba limba l inglesou loco mademoiselle charlotte mait carrefour ma tresse d lai ma tresse hounon gon maman brigitte marassa marassa jumeaux marinette mombu mounanchou nago shango ogoun papa legba pie simbi sobo sousson pannan ti jean quinto ti malice ti jean petro vodun construction workers generally work long hours for their pay labour economics seeks to understand the functioning of the market for labour labour markets function through the interaction of workers and employers labour economics looks at the suppli |
ers of labour services workers the demanders of labour services employers and attempts to understand the resulting pattern of wages employment and income it is an important subject because unemployment is a problem that affects the public most directly and severely full employment or reduced unemployment is a goal of many modern governments two ways of analysing labour markets there are two sides to labour economics labour economics can generally be seen as the application of microeconomic or macroeconomic techniques to the labour market microeconomic techniques study the role of individuals in the labour market macroeconomic techniques look at the interrelations between the labour market the goods market the money market and the foreign trade market it looks at how these interactions influence macro variables such as employment levels participation rates aggregate income and gross domestic product the macroeconomics of labour markets the labour force is defined as the number of people employed plus the numbe |
r unemployed but seeking work the participation rate is the number of people in the labour force divided by the size of the adult population or by the population of working age the unemployment level is defined as the labour force minus the number of people currently employed the unemployment rate is defined as the level of unemployment divided by the labour force the employment rate is defined as the number of people currently employed divided by the adult population or by the population of working age in these statistics self employed people are counted as employed variables like employment level unemployment level labour force and unfilled vacancies are called stock variables because they measure a quantity at a point in time they can be contrasted with flow variables which measure a quantity over a duration of time changes in the labour force are due to flow variables such as natural population growth net immigration new entrants and retirements from the labour force changes in unemployment depend on infl |
ows made up of non employed people starting to look for jobs and of employed people who lose their jobs and look for new ones and outflows of people who find new employment and of people who stop looking for employment when looking at the overall macroeconomy several types of unemployment have been identified including frictional unemployment this reflects the fact that it takes time for people to find and settle into new jobs if one two individuals each take one month before they start a new job the aggregate unemployment statistics will record this as a single unemployed worker technological change often reduces frictional unemployment for example the internet made job searches cheaper and more comprehensive structural unemployment this reflects a mismatch between the skills and other attributes of the labour force and those demanded by employers if four workers each take six months off to re train before they start a new job the aggregate unemployment statistics will record this as two unemployed workers t |
echnological change often increases structural unemployment for example technological change might require workers to re train natural rate of unemployment this is the summation of frictional and structural unemployment it is the lowest rate of unemployment that a stable economy can expect to achieve seeing as some frictional and structural unemployment is inevitable economists do not agree on the natural rate with estimates ranging from one to five or on its meaning some associate it with non accelerating inflation the estimated rate varies from country to country and from time to time demand deficient unemployment in keynesian economics any level of unemployment beyond the natural rate is most likely due to insufficient demand in the overall economy during a recession aggregate expenditure is deficient causing the underutilization of inputs including labour aggregate expenditure ae can be increased according to keynes by increasing consumption spending c increasing investment spending i increasing governmen |
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