What are the arguments for preferring Continental or Analytic philosophy?

Question: It seems as though Analytic philosophy is dominating in my country. Could you give me an argument for preferring Continental over Analytic philosophy, and vice versa, their relative strengths and weaknesses. I'd like to understand both sides of the argument.
Comment: See [Analytic versus Continental Philosophy](https://philosophynow.org/issues/74/Analytic_versus_Continental_Philosophy) as well as N.Levy, [Analytic and continental philosophy: explaining the differences](http://www.jstor.org/stable/24439383?seq=1#page_scan_tab_contents) (2003).
Comment: Does it have to be a competition between the two? I don't see why some sort of mutually productive synthesis can't be achieved.
Comment: Hi, welcome to Phil SE. See Can philosophy overcome "the two cultures" divide? http://philosophy.stackexchange.com/questions/17765/can-philosophy-overcome-the-two-cultures-divide D'Agostini's From a Continental Point of View: The Role of Logic in the Analytic-Continental Divide http://www.tandfonline.com/doi/pdf/10.1080/09672550110058821 and Blattner's Thoughts About "Continental" and "Analytic" Philosophy http://faculty.georgetown.edu/blattnew/contanalytic.html
Comment: @commando Does it have to be a "synthesis"? I'd characterize the choice as more utilitarian -- depending on the topic of discussion, one point of view may be more productive than another. For some tasks a hammer may be more useful than a screwdriver; for other tasks vice versa. There's no need to construct a hammer-screwdriver synthesis. Just choose the tool that best serves the task at hand. And some tasks require the simultaneous use of several different tools to accomplish a "composite purpose".
Answer: Here is the introduction to the biography of Pink Floyd taken from Wikipedia:

Pink Floyd were an English rock band formed in London. They achieved international acclaim with their progressive and psychedelic music. Distinguished by their use of philosophical lyrics, sonic experimentation, extended compositions and elaborate live shows, they are one of the most commercially successful and influential groups in the history of popular music.

This would correspond to the analytic style of describing concepts.

Now here is the introduction to the biography of Pink Floyd taken from Allmusic.com:

Some bands turn into shorthand for a certain sound or style, and Pink Floyd belongs among that elite group. The very name connotes something specific: an elastic, echoing, mind-bending sound that evokes the chasms of space. Pink Floyd grounded that limitless sound with exacting explorations of mundane matters of ego, mind, memory, and heart, touching upon madness, alienation, narcissism, and society on their concept albums of the '70s.

This description is closer in spirit to the continental style of describing concepts.

A proponent of the analytic style will argue that the second description is at best very difficult to understand, and requires someone to know a lot about Pink Floyd before hand at the very least for it to make any sense at all. They would accuse the author of the second definition of being "obscurantist". A "hard core" analytic philosopher, i.e. a logical atomist or a logical positivist will go even further, stating the the second description is meaningless all together (How does one go about "grounding limitless sound" with "exacting explorations"? And what exactly is "limitless sound" anyway?). The first description on the other hand is clear and unambiguous, and carries relevant information by it's logical and precise structure.
A proponent of the continental style will argue that the first description of Pink Floyd, for all of its clarity and unambiguity, fails to convey the true artistic impact of the band. The second description, which uses metaphors and subjective terminology in a way that analytic philosophers don't usually subscribe to, succeeds in giving a better feel for Pink Floyd's influence and it's perception among critics and the public, that a 'mere' analytic description can never convey.
Consider the following quote from Nietzsche (who is retroactively categorized as a continental philosopher) "Thus Spake Zarathustra":

I teach you the overman. Man is something that shall be overcome. What have you done to overcome him?
       All beings so far have created something beyond themselves; and do you want to be the ebb of this great flood and even go back to the beasts rather than overcome man? What is the ape to man? A laughingstock or a painful embarrassment. And man shall be just that for the overman: a laughingstock or a painful embarrassment...

A proponent of continental philosophy would argue that there is no way to fully describe Nietzsche's overman (übermensch) using analytic, clear cut definitions à la Tractatus. You would be forced to use a metaphorical and subjective style if you wanted to convey the full meaning of the overman.
Answer: If you wanted to draw a line back into history, one could say that the analytic tradition descends from Aristotle and the continental from Plato.
The first is more discursive and rational, and the latter more literary and poetic; for example Plato uses myths, parables, metaphors and direct speech whereas Aristotle will give the arguments of several of his established predecessors and look at the question at hand in a distinctly rational mode that has a family resemblence to the mode of enquiring that goes under science now.
They are however both modes of thinking, and there is a cross-over between the two; after all, Aristotle was a student of Plato.
Answer: Analytic philosophy typically deals with narrowly defined topics with great precision, formal (or pseudo-formal) arguments, and aspirations to clarity.  Continental philosophy is likely to take on more ambitious and significant topics, but often treats them solely in a poetic and allusive manner.
Analytic philosophy can be criticized for diminished ambitions and scope, resulting in pedanticism, and an obsession with tedious minutiae.  Continental philosophy can be criticized for obscurity, and the tendency to sound good without saying anything that can be reliably understood, translated into well-formed arguments, or used to establish clear results.  Both can be criticized for engaging almost exclusively with the academic world, to the exclusion of topics of wide general interest and understandability.  (These criticisms, of course, do not apply universally --there are those on both sides who have transcended their peers' limitations.)
Some of the great achievements of each in recent memory are the creation of the science of modern logic for analytic philosophy, and the social and cultural impact of existentialism and deconstructionism for continental philosophy.  To express it another way, continental philosophy has produced great art, and analytic philosophy has produced a great science.


Copied files are disappearing from USB stick

Question: guys. Honestly, I am kind of a new user to Linux and I have recently installed Linux Elementary OS 0.3.2 Freya (64-bit). Everything is perfectly working, aside copying or any transactions with files. Whenever I copy any file to any USB-Stick or Hard-Drive whatsoever, after having unplugged it is not there...seems I have never copied anything. It keeps happening. Sometimes data stay when I, after copying, rename the file. What do you think the problem is and How can it be fixed? Thanks in advance.
Answer: I have seen this issue pop up a few times when trying to copy items to a USB stick in elementary OS. To solve it, I just make sure I am properly unmounting the USB key before removing it.
To unmount the drive in elementary OS please do the following:

Open up the Files app
Find your drive in the Devices section in the left hand menus of the Files app.
Click the unmount icon to the right of the drive in question. It looks like an arrow pointing up.

After you unmount the drive it should be safe to move to a different machine, or even the same machine, to test and verify that your files are still there. Good luck.
Answer: A possible solution is that the USB drive permissions are not set correctly.
The following terminal commands will tell you what the device assignment is and also to change the permissions within the device.
Terminal command to tell you the device assignment for the drive.
    sudo fdisk -l

The device that is the size of your USB device will be assigned a location such as /dev/sda or /dev/sdb. Using the location info you can change the permissions easily with the following command depending on if you only want read and write permissions or also want to execute programs on the drive.
sudo chmod 777 /dev/sdX     <---For Read / Write / Execute

OR
sudo chmod 666 /dev/sdX     <---For Read / Write

Comment: I tried to find out the device assignments but didn't work out. Terminal command simply doesn't work/show. Any other ideas?
Comment: Make sure that you are using the 'sudo' command. Worse case at the login prompt, you can hit CTR + ALT F1 to get to a terminal window and type the commands in. The other option is using a live CD to change the permissions. The last option is use a tool like 'GPart' to be able to redo the disk as a whole. This last option will wipe your data thought.
Answer: My guess would be you haven't unmounted the USB storage. Manually unmounting is very important, since unlike windows the actual writing to the storage is not done automatically (although windows is also asking you to remove USB safely)
You should try clicking the "Eject" button if you are using file explorer
OR
umount /mnt/<add you usb folder here>

from your terminal


Entering Matching gifts

Question: My organization receives gifts which are then sometimes matched by an employer. As it stands now, we are entering the original contribution with no indication of a potential or forthcoming match. Then when we receive a match, we enter a second contribution for that individual and we fill in the Matched From and Matched Amount fields. Is this the proper way to enter these transactions? I had thought that entering these fields in the original contribution would add the matched amount to the total for that individual but it doesn't which is why we enter the second contribution with those fields. Assuming that this is the right way to do this, how can I generate a report which lists an individual's contributions and shows which are matching gifts? Related, what report uses the Matching Funds fields?
Comment: Please provide us some example for the same -
Comment: Sorry, I don't understand. Of what would you like to see examples?
Answer: This isn't really the correct way to record matched gifts. Matched gifts should be hard credited (recorded against) the donor and not the fundraiser so to speak. It sounds as though your recording them against the fundraiser and therefore you could end up claiming tax/gift aid incorrectly. The way we would normally do this would be to record the second contribution against the Employer that carried out the matched giving. At this point you could create the soft credit to the employee. This way you'd see both original gift against the fundraiser and the soft credit for the matched gift also. You'd also get a good idea of the value of employers by virtue of recording the hard credit against them.
Hope that helps!
Comment: Just to be clear. You are suggesting that the matching contribution be entered for the employer and that the "soft credit" be entered as part of that entry. This makes sense for the reasons you mentioned; however, if I look at the "fundraiser" record there would be no indication of the matches. Correct? Or does the "soft credit" go in the fundraiser record?
Comment: The soft credit would also show against the fundraisers record as a soft credit. You can also search for soft credits in the contribution search so there shouldn't be any reason not to do it this way.
Comment: Perfect. Thank you.

Entering Matching gifts


What are the grammatical rules for using filler words in Japanese(e.g. ええと, なんか, あの, and so on)?

Question: I found a bit interesting bits on them through some research, but nothing about what the grammatical rules are for using them all. Any ideas?
Comment: I'm pretty sure there aren't any rules, they serve as breaks in a conversation (usu. for the speaker as they are thinking) so if there were rules that would kind of defeat their purpose.  Think of "um" or "uh" in English, are there *rules* for that?
Comment: Fair enough. What are some of the more commonly used filler words in Japanese, though?
Comment: http://detail.chiebukuro.yahoo.co.jp/qa/question_detail/q1171709961
Comment: You've got most of them down :P, I can't think of anything else right now
Answer: Fillers are speech disfluency. It's part of speech but not grammar.  Use them to fill voids in speech just like English speakers use "Um..", "well..", "like.."


Bicycle Trailer pulls back wheel sideways

Question: I have 2 bikes. A touring bike and a mountain bike. The touring bike pulls my 40 lb daughter, snacks, and water just fine (with a Burley classic hitch). The mountain bike on the other hand pulls for about a mile then the front of the tire starts to cant to the right, eventually rubbing on the frame. This used to happen on my old univega mountain bike when pulling my son.
Anyone have any ideas on how to fix this or why it is happening? Is it because my touring bike is designed to pull a heavier load? Thanks in advance!
Comment: How tight are you doing up the rear wheel QR?  Remember it should leave an indent in your skin as you push the lever closed.  Rotate the lever so its "open" then turn the nuts to close, and finally get the last tension by flipping the lever from Open to Closed.
Comment: What style of dropouts do the bikes have? Photos of the rear wheel mount/dropout area on both bikes would help a lot.
Comment: How is the trailer attached?  If via one of side hitches, it may not be properly set up.
Answer: It is possible that you put not enough torque on axle nuts. The axle moves in the fork.
 If there is enough space, add some extra, broad spacers and then screw it back to the frame.
Use this kind of spacer (it's from Sram I-3, might require some drilling)
Answer: Have you ever changed the back wheel for one with a wider axle?
I get a similar effect on my old 15 speed MTB, which was a 5 speed rear.  When I fitted a wider wheel with a 7 speed freehub, the dropouts needed spreading by a couple millimetres.  I did not parallel the dropouts, so they're very slightly shaped like    / \
The upshot is that the Quick Release doesn't bite into enough metal, and sustained hard pedalling allows the wheel to move in the dropouts, eventually giving frame rub on the left chainstay - torque through the chain and cassette on the right-side pulls that side forward.
In your case, I imagine the trailer hitch is on the left side and the overrun pushes the axle forward.
So, the temporary fix is to do the QR up really damn tight, or to use axle nuts done up tight, or even to use softer metal washers which will deform and fill up more space between dropout and axle nut.
The proper fix is to bend the dropouts back into line by cold-setting the steel frame.  This takes power and leverage, and patient measuring.
Comment: This, and krzyski's answer, match my experience (on a bike that has had dropouts stretched). Putting some extra force on the pedals (riding uphill, setting off) can have the same effect with my two kids in a trailer. This is more common after the wheel has been off the bike. Tightening the skewer an extra quarter turn and re-setting the wheel gets me going just fine. If you can't tighten the skewer and still close the quick release, you could try a different skewer.


Till which layer does the loopback packet goes?

Question: I want to know exactly till which layer in the OSI model the 127.0.0.1 (loopback) packet goes till it is returned to the upper layer. I read some where it goes till data link layer. but as i was told data link layer cannot see the ip address then how data link layer decide that the packet has to be send "up" instead of "down".
Comment: Should go somewhere else, probably ServerFault.
Comment: I can't understand what you're asking. What do you mean by "till which layer... the packet goes till it is returned to the upper layer"? Or, more generally, by a packet "going till a layer"?
Comment: @G.Bach Definitely not Server Fault, which is for professionals only (and extremely jealous of that). Since this thing is taught in CS classes and not just in engineering classes, I think the question is ok here.
Answer: When you say "layer", you are probably thinking of the OSI model, also known as the seven-layer model.
However, real TCP/IP implementations don't actually fit the OSI model very well.  The OSI model was designed by a standards committee 30 or 40 years ago, based on how the committee members thought network stacks ought to be designed -- but that was before the Internet and without the advantage of the experience we have today.
127.0.0.1 is an IP address, and the loopback functionality of 127.0.0.1 is associated with the IP protocol.  The IP protocol can be thought of as most closely associated with the "network layer" (in the OSI model).  So, you could say that the answer is "the network layer".
But, it's important to realize that this is a bit of a lie.  In real operating systems, there's not necessarily a clean separation between the TCP stack and the IP stack; the two are closely hooked together.  So, it's doesn't make sense to ask "the code that does loopback processing -- what layer is it at?".  The code that does loopback processing could plausibly be considered part of the TCP/IP stack, and the TCP/IP stack combines elements of the network layer, the transport layer, and the session layer.  Loopback processing might also be performed in a separate device driver that, from the operating system's perspective, looks like another device (just like another Ethernet card, but different), so one could even make an argument that the code is really part of the data link layer or physical layer.  See how the seven-layer OSI model isn't really adding much insight here?  The code is what the code is; trying to attach a label based on one of those seven layers is a human construct, one that in this case isn't a very good match to reality.
It's probably better to think of the OSI model as a plausible vocabulary for talking about network protocols, but it's less helpful when talking about the structure of networking code: the structure of the code doesn't necessarily correlate well to the seven layers of the OSI model.
TL;DR: the OSI model is a lie.
Comment: @DavidRicherby, it was definitely meant as a design template for networks, but was misguided (it contains layers that make no sense in computer to computer networks, like the whole session layer) and others that are an overengineered "solution" to a non-problem (presentation layer). Its real relevance is in the lower layers (physical, data link), but even there e.g. the IEEE 802 standards subdivide the layers and define different functionality. The TCP/IP model was in fact previous to OSI, and outlived it for 20+ years now.
Comment: I'm not sure the OSI model is really "a lie". But it's definitely better to view it as a vocabulary for talking about networks, and not as a design template.
Comment: Basically i am preparing for an exam. and this question may be asked there. the theory which we all read says Data link layer. but i think it should be network layer. now i am confussed which layer i should use.
What u suggest for that.
Answer: Simple answer: The 127.0.0.1 address is an IP layer concept, so it has to be handed to the IP layer for correct routing and so.
More complex answer: The 127.0.0.1 address might be common enough in practical use that upper layers of the TCP/IP stack in your particular operating system cut corners and handle it specially. Even your application might figure out it is supposed to talk to itself and never touch the TCP/IP stack.
No, the totally misguided (and finally dead and buried) OSI protocol stack has no relevance to any of this.


Cooking Wine in a Gas Oven?

Question: I've got my first gas stove / oven. I'm wondering about cooking wine in the stove. Is it safe at all? I like putting a piece of meat in a all stainless steel pan, brown it a bit on the stove then throw it in the oven to finish off. For certain cuts I'd add something like burgundy wine and some vegetables as well. I'm just not sure about doing this in a gas stove and couldn't seem to find any existing questions or articles on the topic (Searched for "Cooking wine in gas stove" and similar).
Comment: I imagine OP worries about the alcohol fumes might ignite and blow up the kitchen.
Comment: If, even after jurgemaister's answer below, you are still concerned about the alcohol igniting, then you could do the following: After you have browned the meat in the stainless steel pan, you could add the wine and keep the pan on the stove for a few minutes until most of the alcohol has evaporated, before putting the pan into the oven. In fact, once the wine has been heated, you could attempt to ignite it's fumes while on the stove, which may also add some more caramelisation to the sides of the meat.
Comment: I can't for the life of me figure out what you're worried about here. Can you be specific? What do you imagine will go wrong?
Comment: That was my assumption too @jurgemaister. If that's the case, it might be helpful if Ryan edited the question to make that more clear.
Comment: @PrestonFitzgerald I've read the question and while ignition is the main question any other safety concerns are also relevant and thus my question is fine as is. It very clearly states, "Is it safe at all?" If the answer is yes and someone wants to say yes as an answer I will mark it as such. If there is some safety concern whether fire hazard or anything else to be aware of when using wine in a gas stove then I'll mark that as the answer.
Answer: I assume you are talking about the risk that the alcohol vapor from the wine mixes with the air and ignites.
Let's do some maths. I'll do my calculations with some pretty round numbers, but in the end you'll see that it doesn't matter.
Assume an average gas oven with a volume of 150l. According to Wikipedia, the absolute minimum mix of ethanol to air for ignition is 3%, so that's 4.5l of pure ethanol vapor.
Water expands at a rate of 1700 when it turns into steam. Assuming ethanol is in the same ballpark and add some entropy for higher temperatures, we'll assume a factor of 2000. That means we'll need 4.5l / 2000 = 2.25ml of pure ethanol.
In a typical bottle of red wine there is 12% ethanol, so for a 750ml bottle, that is 90ml.
As you can see, we have about 40 times the ethanol we need to make a nice boom.
Now to answering your question:
I would deem it probably safe to cook red wine in the gas oven. The burners are usually not in direct contact with the air inside the oven, and both the burners and oven is ventilated, so the ethanol would probably escape even before it could meet the required saturation. And even if the vapor was allowed to build up inside the oven and not get in contact with the gas flames, the self ignition temperature for ethanol is 363°C, far hotter than it'll get in there.
The most convincing argument that it's safe is the millions of times chefs around the world have cooked with wine in a gas oven :)

Cooking Wine in a Gas Oven?


Why community in SE deleted my comment related to the below duplicate question?

Question: Really am sorry for the behavior of community of stackexchange math, I am the first who  has marked  this question as a duplicate question and I have got some up vote for this comment  After sometimes, I have got my comment deleted and the question become marked by others, Why this behavior? Really I decide to leave this website this is not good behavior
Comment: Just to be explicit, the *upvotes* are also automatic. A comment is automatically generated when someone flags/votes to close a question as a duplicate. Each additional vote to close (and flag?) will cause the comment to be upvoted. (The comment can also be upvoted in the normal manner too, though.)
Comment: The automated removal of Comments that identify the duplicate will in some cases also take away an observation that would be helpful to the OP (original poster) or other Readers.  If that was the situation here, feel free to restate your Comment or a variation on it in light of the vote to close-as-duplicate.  And my thanks for helping with Community Moderation in this fashion!
Comment: Why does it even matter that you flagged this, people agreed, and then the question was closed by others? Clearly you could not VTC yourself or I expect you would have done so. The only behaviour needing apology is your own, for instead of simply asking why something happened, you complain that others must have done some wrong to you, badly enough to leave the site.
Comment: @zeraouliarafik As explained above and by quid in the answer below, it's an automated software result. I believe it's something which is the same system wide. Thus, you can check if anybody has made a request in the main meta site, i.e., https://meta.stackexchange.com , to change this behavior and, if not, you may wish make such a request yourself.
Comment: @DerekElkins One small addendum to what you stated which has occurred to me is that when I've used up my quota of comment upvotes for the day, casting a vote to close a post as a duplicate then doesn't cause an automatic upvote of that comment.
Comment: You can see your flagging activity at https://math.stackexchange.com/users/156150/zeraoulia-rafik?tab=topactivity by clicking "helpful flags" in the top left (you can't see other users' activity, just your own).  So you'll be able to see that your flag was indeed helpful.  Be aware though: sometimes clicking that link does take some thick skin when you see that others in the community disagreed with your flagging.  As long as those disagreements are sparse, you're doing fine and should ignore the occasional disagreement.
Answer: I am sorry for the frustration, but it is of nobody's doing, specifically.
The automatic comment posted upon a vote to close as a duplicate or also a flag as duplicate, the current case, gets automatically deleted by the software once the vote takes effect, because it is considered as redundant. As a general principle comments that are no longer essential get removed.
The people listed in banner are those that voted to close as a duplicate, while you had flagged as a duplicate. Soon, once you reached 3000 points, you will be able to cast a vote as a duplicate, too. In this case the comment will still be deleted, yet you then will be listed in the banner.
Indeed, unfortunately, the information that you had flagged as duplicate is now not very visible anymore. It might be that this side-effect was overlooked, due to the fact that flagging for duplicate is a latter addition, and it is less of an issue for voters (but I am not completely sure about this).
In any case, your flag was useful and appreciated.
Comment: I am glad that I could have been of help. Thanks again for the flag.
Comment: Am sorry for that i don't know about "banner list law " , Thank you so much


Router FTP upload

Question: I have a USB drive connected to my hg556a router from Vodafone (manual).  I'm attempting a backup using FTP via wired ethernet -> router -> USB2.0.
On wireless it managed two simultaneous uploads at approximately 80kbps, so I am trying wired instead.  Via a wired connection it can only do one transfer at a time (via wireless it was two - on wired the second attempt in FileZilla continually gets rejected by the router), and it's not much faster at about 120kbps.
Those speeds are not good enough for a network media/backup drive.  I would expect the upload speed to be close to 1Mbps (limited by the ethernet connection).
What can I investigate to improve this upload connection speed, and get the second FTP connection working again via the wired connection?
I'm using Ubuntu on the uploading computer.
Answer: Try install a custom firmware such as Openwrt because you can tweak the USB drive's mounting parameters to improve your USB write speed.
I can achieve a few MB/seconds write on my router running Openwrt.
Comment: What tweaks did you make to do that?

Router FTP upload


Can fixed scope + fixed deadline + fixed price contract ever be made to work with "agile"?

Question: Some projects we run internally using are Scrum, while still being "fixed everything" to the customer.  We're experiencing mixed success on our part (the customer likes the visibility of the burndown chart). Can the types of projects we work be successfully executed using the agile methods?
Comment: Can fixed scope + fixed deadline + fixed price contract ever be made to work?
Comment: Isn't this a way to rephrase: "Fast, Good or Cheap. Pick Two" ?
Comment: Isn't fixed an antonym of agile?
Answer: I would like to pose a counter-question:
Can fixed scope + fixed deadline + fixed price contract ever be made to work, period?
The "good/fast/cheap - pick two" saying isn't just some silly engineering joke.  Every project manager worth his salt knows about the Project Management Triangle:

You're telling us that the cost, scope, and schedule are all fixed.  That leaves no room for maneuverability or error.  None.  You could choose to view "Quality" as an attribute, but it's not a "real" attribute, it's more like a meta-attribute that's derived from the other attributes (cost/scope/schedule).
The problem is that this never happens in reality as long as your project is being planned and executed by humans.

Requirements and specifications never cover every edge case unless they've been drawn up in immense detail by qualified architects and designers, in which case the project is already half-done; and even then there's still the possibility of error.
Unexpected costs will pop up leading to budget overruns.  A subscription expired.  A manufacturer discontinued their support for a product you're using and you have to find a new one.  An hourly contractor raised his rate under threat of departure.  Your entire team just went on strike, demanding a 10% raise and an extra week of vacation.
Schedules slip.  Unforeseeable problems crop up; that charting component you've been using for 5 straight years isn't compatible with Windows 95, which your client is still using.  An obscure bug in 64-bit Windows causes serious UI glitches and you spend nearly a week tracking it down and developing a workaround (this actually happened to me).  Your senior developer got hit by a bus and you have to go recruit and train a new one.  Your estimated delivery date is always wrong.  Always.
See Hofstadter's Law:

Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.

Agile methods are all about juggling around the cost, schedule, and scope.  Most of the time, they're specifically about juggling around the scope and sometimes the schedule, which is why you start with nebulous user stories and plan revisions instead of full versions.  Different methodologies use different terminology but it's all the same basic premise: Frequent releases and a rebalancing of the schedule and scope with each release.
This makes no sense with a project that is (or claims to be) either fixed scope or fixed schedule.
If one project attribute (cost/scope/schedule) were fixed, I would tell you that it might not be a good fit for agile methodologies.
If two project attributes are fixed, then your project is definitely not a good fit for agile methodologies.
If all three attributes are fixed, then your project is probably going to fail.  If it actually ships, then either the original schedule was massively fudged, or the client has managed to delude itself into thinking that you actually delivered what was promised.
If this contract is still on the table, I urge you to reject it.  And if you've already accepted it, may God have mercy on your soul.
Comment: +1 for Hofstadters law.  I'm going to quote it at the next estimating session.
Comment: Fixed schedule / scope / price projects can work (I've done them), they just require really solid requirements, really good estimating and as you say these things are very hard in reality.  +1 for a clear explanation of how Agile is basically contradictory to the whole fixed price mechanism though as one is all about (smart) trade-offs and the other precludes the possibility of trading off anything.
Comment: Just the amount of upvote on this answer shows how many are toiling away in Agile + Fixed price mess.
Comment: Note that if "fixed" doesn't really mean *fixed* (as implied in the comment to Todd's answer) then that changes the landscape somewhat, and the success of the project will partially depend on getting everyone to agree on the actual definition of the word "fixed" (or "must" or "required" or whatever the specific verbiage in the contract is).  If the scope is really *"fixed if we have time"*, then it starts to look a lot more like an agile project. :)
Comment: I suspect that that's how the management have worked it with the client.
Comment: +1 I will now refer all questions or answers involving fixed bid to this answer rather than explaining it all again myself.
Comment: BTW I have been using a more succinct version of the triangle for some time with some success: "When or what, pick one."
Comment: +1 for saying what I was going to, more eloquently than I was going to say it.
Answer: I love this quotation:
"Scrum is great for either fixed-date variable-scope, or "fixed-scope" (which always grows) variable-date. If you're doing fixed-date fixed-scope, I recommend waterfall or RUP, which will buy you a few months to look for a new job."
   ~Michael James
Answer: Well, I've worked mostly in "agile" environments (although we don't use the lingo), and I've done fixed cost things.  Generally what it amounts to is cost-plus, since no company can afford to do everything for free, and requirements do change and evolve as the customer figures out more clearly what they want.
The initial requirements for the fixed cost portion have to be done much more carefully than they are done in a typical iterative environment, making the process somewhat less iterative.  The "plus" part of the contract can be more iterative, provided we have fulfilled the fixed cost portion more or less satisfactorily to the customer.
Answer: Sure, as long as your quality bar is kept remarkably low. I'm a believer in the old iron triangle of "delivery time / quality / price" where you can pick two, but then the other one floats. It sounds like you've fixed the delivery time and price (and also the features) so really the only thing that can give is the quality.
That said, if you're using a burndown chart and you have the highest priority items being done first it might be acceptable to have a handful of the most important items done in the specified time-frame for the specified monetary amount. At the very least your client will see that you are controlling the process somewhat, with a deliverable at the end of each iteration and they have the ability to say what's most important.
Otherwise I think that committing to a fixed time, feature set and price is foolhardy and will lead to heroic efforts resulting in lower quality and less maintainable code. Agile is not magic fairy dust.
Comment: That's pretty much how we've handled it with our customer - let the scope slip and add it in the next version.  Their prime motivators are deadline and price.  We don't like to let quality slip - as this and the other comments note, we're fully aware the triangle - the business side has the fun job of making the customer aware of this too.
Answer: Fixed price / fixed deadline / fixed scope can be done at least as well agile as it can be in waterfall.
In waterfall, time estimations are inaccurate, and details end up being implemented differently than the original specifications.  In other words, the deadline/scope can't be known exactly in advance.
In agile, you can do sprint zero to generate a backlog of user stories, and make some estimations.  Then agree to meet the value stories for a fixed price, by a fixed deadline.  The scope is fixed in terms of the value stories that you intend to fulfill, and no promises are made about user stories.
In other words, you promise to deliver what matters, and avoid making promises about specific design decisions that are unrelated to the revenue/savings/etc. that the project is supposed to deliver.
Comment: Old, but... it could be done infinitely better in Agile than it is in Waterfall, and the odds would not change. Zero is always going to be zero. If a single task on a single story encounters a single event that changes the cost or effort, you have failed.
Answer: I agree with Bruce to a certain degree.  Though I am not too familiar with waterfall or RUP, and thus cannot comment on that.
What I read recently, and I thought was really well said, was that even in Agile we neglect planning.  A thorough planning session once an iteration is great - no it's essential - but so is planning THROUGHOUT the iteration.
I work in the entertainment industry, where things are constantly changing.  The team needs some degree of leniency / flexibility which will allow them to "re-plan" stories mid sprint in order to align with new goals or revised goals.
I love the idea of continuous planning, as too often developers will tell the product owner to go away when they're working on stories mid-sprint.  This is excellent if your team works on stories which are still valid, and your product owner is just being a nuisance.  But in some instances stories become redundant DURING the sprint, and it is imperative for the product owner to spot this, and for the team to re-align with changed goals / stories - isn't that what agile is about?
Comment: if you're doing constant planning, then Scrum really isn't for you. Kanban might be a more appropriate one to try. But what you say about Agile being about is spot on.


How to solve 0.5 choose 4?

Question: I was solving this problem for homework. It says, in the problem, that if n is positive you use the generalized definition of binomial coefficients. In my case, n is positive so I just plugged n= 0.5 and r=4 into the equation n!/r!(n-r)!. However, now I'm having issues solving (n-r)! because I'm having to take the factorial of a negative number. Can someone just explain how I would go about solving this part?
Comment: See http://en.wikipedia.org/wiki/Binomial_coefficient#Binomial_coefficient_with_n_.3D_.C2.BD.
Answer: $${n \choose k}=\frac{n(n-1)\cdots(n-k+1)}{k!}$$
You can apply this definition to noninteger $n$, so here
$${\frac12 \choose 4}=\frac{\frac12(\frac12-1)(\frac12-2)(\frac12-3)}{24}=\frac{\frac12(-\frac12)(-\frac32)(-\frac52)}{2^3\cdot3}=-\frac5{128}$$
Comment: They had the same exact definition in the book, but I plugged it in wrong. Thank you!
Answer: I believe it goes something like this:
$\dbinom{.5}{4}=\dfrac{(.5)!}{4!(.5-4)!}=\dfrac{(.5)(-.5)(-1.5)(-2.5)(-3.5)!}{4!(-3.5)!}=\\ \quad \dfrac{(.5)(-.5)(-1.5)(-2.5)}{4!}=-\dfrac{15/16}{24}=-\dfrac{5}{128}$

How to solve 0.5 choose 4?


Out of USPTO and GCC which one should be filed first?

Question: I want to protect my invention in gulf and US both. Now shall I first file in Gulf (GCC) and then move to USPTO or the V.V ?
Answer: If you reside in Gulf Cooperation Council (GCC) country, e.g., Saudi Arabia, then you would typically file in your home jurisdiction first (e.g., via The Patent Office of the Cooperation Council for the Arab States of the Gulf) and then use the Paris Convention or the Patent Cooperation Treaty (PCT) to pursue patent protection abroad while maintaining the benefit of priority to your home country filing.
However, if you reside in the US, then you would typically perform your first filing with the USPTO.


Quantum Decoherence and Macroscopic Phenomena

Question: I don't really know what quantum decoherence is, but I have heard that it is used to explain why macroscopic objects do not seemingly follow quantum dynamics.  Could someone please give a simple explanation of what decoherence is and why it follows from it that macroscopic objects do not seemingly follow quantum dynamics.
Comment: If you have some familiarity with quantum physics, read this: http://arxiv.org/abs/quant-ph/0105127
Comment: For a nice toy model, see http://arxiv.org/abs/1009.1282v2
Answer: In quantum dimensions, i.e. order of hbar, matter has a dual nature, particle and probability wave.I.e depending on the experiment one will find particle attributes or wave attributes.
An example of particle behavior is the photoelectric effect: a photon hits an electron which is ejected and leaves an ionisation track .
An example of the wave nature is the two slit experiment, where there is an interference pattern even if individual electrons go through one at a time.
Waves are characterized by an amplitude ( in the qm case a probability when squared) and a phase. The phase is the angle that a particle's  wave function   has as it is oscillating,  phi in the paragraph of the link "amplitude and modulation". When one particle interacts  with the wave function of another particle the phases between the two wave forms will define their interference and beats, both classically and quantum mechanically.
Phases are important for classical waves too. Coherence between waves means that the angles between them  remain constant in time and space and thus coherent beats can appear and interference patterns. If the phases between waves are random no interference patterns can appear. That is what the term "decoherence" means, classically and quantum mechanically: the correlation of the angles/phases  is lost.
When one has more than two particles, each with its wave description, it is easier to lose the coherence between waves than to keep it. Avogadro's number says that there are  6.02214X×10^23 molecules in a mole. Even though each molecule in the mole has its QM wave function and QM phase, statistically the number is so huge that unless special conditions are carefully imposed the QM phases between the particles are lost and the quantum mechanical behavior is obscured.
Under special conditions, superconductivity for example, or superfluidity, the quantum behavior of the phases is maintained and the QM phases kept so that there is coherence and one observes macroscopic quantum mechanical effects.
Crystals also fall under the special conditions where coherence is maintained and we macroscopically see the effects in the symmetries of the crystal.
Answer: Fragments of the environment continually interact with quantum systems. Initially uncorrelated, they become entangled. This entanglement washes out interference of the quantum system.
Answer: I wrote a paper (review) on arxiv on decoherence and decoherence in complex systems for those "Can we advance macroscopic quantum systems outside the framework of complex decoherence theory?"   `http://arxiv.org/abs/1312.7835
www.markbrezinskimdphd.com


Are there any enharmonic chords?

Question: Will I even encounter any enharmonic chords? For example, would an inverted variation of one chord be equivalent to the root variation of another chord?
Comment: Well, accidentals are usually what define enharmonics... I might actually put _enharmonic_ in quote marks in your question, just to make that a little bit clear... or not even use the word at all; rather just ask "Are there any chords that can have more than 1 valid name?"
Comment: What NReilingh and jjmusicnotes said. I'd like to add that chord inversion is yet another, mostly different aspect that is completely separate from enharmonic equivalency. For chord inversion, the following usually holds: 1st inversion (3rd in the bass) is usually harmonically equivalent to the root position chord. The 2nd inversion (5th in the bass) almost always has a different function than the root position chord. It's often treated as a suspension of the chord a fifth above it. So GCE (2nd inversion C major) is heard as a suspension that resolves into GBD (G-major root position)
Comment: I presume your question is outside the scope of, say `Dbdim` being enharmonic to `C#dim`, yes?
Comment: Right, besides accidentals.
Comment: Agreed with NReilingh here - enharmonic refers to multiple ways a sounding pitch can be notated.  The OP appears to be asking whether or not two differently-named chords could contain the same notes.  See Dom's answer below.
Comment: The term you want is not "enharmonic" but "inversionally equivalent"
Answer: Yes they exist. I don't know all of them of the top of my head, but I'll give you the three that come to mind easily.
The first is a fully diminished chord. Because there are only 12 named notes and a fully diminished chord is made of 4 notes that are a minor 3rd apart from each other (3 semitones) there are only 3 different chords but each can be named 4 different ways. For example, a C fully diminished chord would consist of the notes C-Eb-Gb-Bbb, a Eb fully diminished chord would consist of the notes Eb-Gb-Bbb-Dbb(C), a Gb fully diminished chord would consist of the notes Gb-Bbb-Dbb-Fbb(Eb), and an A (Bbb) fully diminished chord would consist of the notes A(Bbb)-C-Eb-Gb.
The second is an augmented chord and like the fully diminished chord because there are only 12 named notes and an augmented chord chord is made of 3 notes that are a major 3rd apart from each other (4 semitones) there are only 4 different chords but each can be named 3 different ways. For example a C augmented chord would consist of the notes C-E-G#, an E augmented chord would consist of the notes E-G#-B#(C), and a G# augmented chord would consist of the notes G#-B#-Dx(E).
The third example are 7th and 6th chords. Some minor 7th chords contain the same notes as 6th chords. For example a C6 would contain the notes C-E-G-A and an Am7 would contain the notes A-C-E-G.
In all these examples you name the chord based on the context of the key for example if you are in the key of Db minor and you see the notes Eb, C, Gb, and Bbb you would call that a C fully diminished chord because C is the leading tone of Db minor so it makes the most sense in the key.
Another example is there are polychords and extensions that will contain the same notes. A very simple example is Eb/C (produced Eb over C) can be represented as an C7#9. While the notes of each are the same, a polychord refers to a specific idea where there are two distinct perceived chords rather then just one.
Comment: Another good one is the German Augmented 6th chord, which can be enharmonically respelled as a dominant seventh chord. E.g. Gr+6 in c minor is Ab–C–Eb–F#, but could be used as Ab–C–Eb–Gb, or V7 of Db.
Comment: To expand on Dom's answer, it is not confined to tertian harmonic practices; you can also include **Set Theory** and **12-Tone Technique** here as well.  In set theory, you can not only have different sets containing the same notes (K or Kh relationship) but different sets can also contain the same *intervals* (Z-complement relationship.)
Comment: There's another pair: Dm6 contains the notes D-F-A-B; Bmin7b5 has the notes B-D-F-A, where F is the flattened fifth.
Comment: The most likely candidates here will be the symmetrical chords (dim and aug) as all the intervals from note to note are the same.  The m7/M6 chords can be called either but in most situations there will be an obvious choice.  You will probably never see a chart that has a M6 chord with the 6 in the bass (ie C6/A).  Almost anyone analyzing that harmony would call it an A-7.  Similarly, most would analyze A-7/C as C6.  I actually recall reading in Mark Levine's 'The Jazz Theory Book' that he says there is no such thing as A-7/C, that it is definitively C6, which I would tend to agree with.
Comment: And all (full) 13th chords are inversions of another 13th chord (actually, six more), since they all have all the notes of the scale.
Answer: I will avoid the debate in the comments about whether "enharmonic" is the correct word.
But yes there are loads of examples of chords with the same notes in them.
Example 1
C D G = Csus2
G C D = Gsus4
Example 2
A C E G = Am7
C E G A = C6
Example 3,4
The full diminished and augmented chords where any one of the notes can be considered a root without even changing the type of harmony:
B D F Ab/G# (full diminished)
C E ab/G# (augmented)
Example in use and conclusion
The best name depends on context, that is what chord it precedes and follows, more than it does on the inversion used.
The following (rather overused) chord progression I heard recently in a local band's song springs to mind:
C Am F G
At the end of the song it went uptempo and the chord progression changed to the following:
C6 Am7 F G
But the C6 and Am7 were exactly the SAME CHORD, completely blurred together.
EDIT: John Lennon's Happy Christmas (War is Over)
Just occured to me this is a good example of why you need different names for the same chord. If we look at the chord progression over the first half of the verse, it's easy even for a non musician to appreciate the symmetry and realise why this song is so popular. The fast change through chord type (3rd, sus2, sus4 and back to 3rd) combined with the slow change through chord root (A B E A) make this song both energising and soothing at the same time.
A Asus2 Asus4 A
Bm Bsus2 Bsus4 Bm
E Esus2 Esus4 E
A Asus2 Asus4 A
Now, Esus4 and Asus2 contain the same notes. If I wanted to standardise the name of this chord I could pick Asus2. Applying this rigorously I get
A Asus2 Dsus2 A
Bm Bsus2 Esus2 Bm
E Esus2 Asus2 E
A Asus2 Dsus2 A
Which is totally confusing and completely misses the point of the chord progression.
Comment: The example from Happy Christmas (War is Over) is excellent!
Comment: C+D+G don't make a 9th chord.Generally it'll need a maj/min 3 and a 7/b7.It may pass as a cadd9.
Comment: @tim I checked and you are right, I didn't realise stacked thirds were applied so rigorously. I taught myself theory with a good head for maths, but nomenclature sometimes escapes me. I've seen guitar books that call this chord a 9, so I have been misled. I have changed it to a sus2 which is definitely right. Cadd9 would need an E as well, so unless I call it C5add9 that's not right either. (C5 is a way of saying "no third" that is widely accepted in rock but I don't know if it's accepted in classical.) By the way, what's the correct name for the chord I call "full diminished?"
Comment: @steveverrill, half-diminished and fully-diminished are terms in common use, so the chord you call 'fully diminished' is, fact, fully diminished. Most folks would just say 'diminished,' though, and would only qualify a half-diminished (aka minor 7b5) chord.
Comment: OK, so the rhythm guitarist's sheet music for that song would need chord symbols like Asus2. But for the purpose of analysing the song's harmony, I think you've over-analysed. The 2s & 4s of the sus2s & sus4s aren't harmony, they're another melody line. The harmony is just A Bm E A (4 bars each). BTW, notating all the sus2s & sus4s, the 3rd line is *Esus4 E Esus2* E. And to be fair to the view you aim to refute (notating each sus4 as sus2 would be wrong) the Esus4 had better be not Asus2 but Asus2/E, acknowledging the E bass.
Answer: There are chords that function in different ways in different contexts.  Take for example the chord C-E-G-A.  This is the tonic chord of the key of C major with an additional note.  It is called an "added-sixth" chord.  It has a very pleasing sound and is often used as an ending chord in jazz and in the music of Olivier Messiaen.
Now play C-E-G-A on your keyboard, but follow it with C-D-F#-A and then B-D-G.  As if by magic the chord has become the first inversion of the ii7 of G major; the "dominant seventh of the dominant seventh".  Same notes, but what was a restful ending chord is now a chord that has to move in order to resolve.
Comment: I'd analyse your second example as IV6 V7 I. So the chord in question does indeed function in two different ways but I'd analyse it as having C as root in both cases.
Answer: I realize that this is in some sense the dual to what you asked, but here's one of the most famous chords in music history, the Tristan Chord. 150 years after it was first played, still nobody can agree on how to interpret (and thus name) that chord.
Answer: Yes, for example the min9 is actually a maj13, 3 semitones away
E.G. Gmin9 = BbMaj13
Very useful in jazz when you want to move somewhere other than the predictable (ii-V) patterns, e.g. if G wanted to move to C it can now instead move to Eb (Bb being the 5th Eb as G is to C). It's good to know and gives more options.
Comment: B♭maj13 should also contain the note C, the major ninth. [B♭ D F A G] would make B♭maj7(13), aka maj7add13.
Answer: I don't think there are nor have I ever encountered any. It is mainly because when the notes in a chord are being played, no matter in what order, they all give the same feel as if they are being played together (due to the delay of the previous notes in your head). There are "enharmonic scales" though, for example harmonic minor scale (1 2 b3 4 5 b6 7) and phrygian dominant scale (5 b6 7 1 2 b3 4) both consist of the same notes.
Comment: Major and minor 6th chords usually contain 1 - 3 - 5 and 6.
Comment: yes there are enharmonic chords. A 6 chord is usually the same as the inversion of another chord: for example CM6 (C, E, A) is the same as the first inversion of Am.

Are there any enharmonic chords?


How Many Poems Does a Chapbook Typically Contain?

Question: I'm sure it varies a bit (both in length and in number) but, on average, how many poems does a chapbook contain?
Comment: Look at your bookshelf. How many do the chapbooks you own have?
Answer: This guide to creating a chapbook (PDF) suggests a length of 20 to 30 pages with no more than one poem per page, so roughly 25 shorter poems. If a poem takes more than one page, it would be inappropriate to start the next poem on the same page the previous poem ended, so assuming 12-point font, 8-inch high page, and roughly 1 inch top and bottom margins, one might fit 36 lines per page.
Wikipedia indicates "up to about 40 pages", which agrees with this Writer's Digest blog post. This would suggest a maximum of about 40 poems.

I personally feel that for very short poems, the restriction of no more than one poem per page is stingy. While fitting two sonnets with titles onto a single page would be cramped, two title lines and 16 body lines (including spacing lines between stanzas) might reasonably fit on a page even with a font size that is comfortable for relaxed reading. However, one may be unlikely to have two such very short poems which are close enough in theme to work on a single page.
Comment: Posted as community wiki because this represented little research effort (following a few links from the first page of Google search results for "poetry chapbook length") and minimal personal knowledge.
Answer: Most presses that publish chapbooks give a range of pages they require. The smallest size for a chapbook I have ever seen was ten pages. That particular press called for a maximum of fifteen pages which is unusual; some refer to a chapbook that short as a "mini chapbook," and some small presses specialize in them. They are likely to be more like pamphlets than books at that size range.
The average size is from 20-32 pages, but I have seen a press call for submissions of chapbooks asking for them to be from 30-42 pages. If you are self-publishing, 42 pp is also considered full-sized book length by some presses. General guidelines that are not press-specific are only useful if you are self-publishing, but what I've given here are the perimeters I've seen in the industry. As to how many poems to fit on the page, the standard practice is one poem per page, allowing an exception for two or more haikus or very short poems per page. However, if a single poem runs even one line over a page, no poems are usually placed on that page which contains the extra line. In other words, each poem must begin on a new page.
Chapbooks can also contain prose or mixed genres. The entire chapbook can be one essay or creative nonfiction piece, one piece of fiction, or multiple pieces of any of these. In this case, it is still common practice to begin each piece of whatever genre on a new page, regardless to however much empty space is left from the preceding piece.
Length of chapbooks is measured in pages, not pieces, be they poems, flash, or anything else. They can contain the work of one or multiple authors. They may include visual artwork, or not.
Answer: The Culver City Centennial Collection recently came out with our poetry in it, so I am basing this comment on this publication:
66 poems of various length but most long up to 32 lines per page.
The book contained 98 pages of poetry and 115 pages including a short bio of the poets.
Comment: That sounds like a book, not a chapbook.
Comment: Yes, no book of 98 pp would ever be called a chapbook. The maximum number of pages I ever saw in a small press' guidelines for chapbooks was 42 pages and that was highly unusual. Normally they run no more than 35 pages.
Comment: 35 pages would be a fairly odd length for a book ;)


Miner enquiry for exchange bought crypto

Question: If i buy crypto currency on an exchange with paper money. Do miners have to confirm that i now own X quantity of a  BTC or whichever coin or token I may have bought, is this then confirmed by all nodes on the blockchain? Cold storage devices, any recommendations or referral to past questions or sites? thank you
Answer: Confirmation is required when cryptocoins are moved from one address to another. If you've only just bought your coins, then they're still at an address belonging to the exchange; which means the change-of-ownership is purely an entry in the exchange's private ledger and miners are not involved. The coins are only as safe as the exchange's security and solvency allows.
When you withdraw your coins to some other address (e.g. an address that has its private key in your personal wallet), then yes you do have to wait for miners to confirm the move. Once the miners have confirmed, the coins will be under the control of whomsoever controls the private key for the new address (ideally just you!).


How to practice jumping over cars with disc brakes and SPD shoes?

Question: This question here raises a sub-question, to avoid accidents. I am looking for some safe ways to practice jumping over cars. I use SPD shoes and disc brakes because I have noticed that I can burst very fast with them. I have no idea whether it is possible to jump over cars easily without SPD shoes and disc brakes. So any good ideas for safe practising?
Comment: Do you mean jumping onto cars to avoid being hit, like the moz's answer indicates, or jumping as in BMX-style jumping?
Comment: Very very carefully, wearing as much protective gear (helmet, knee/elbow pads, etc) as you can. :)
Comment: @Neil Fein: to avoid being hit (although BMX-style jumping may be good idea, not sure yet what it really means).
Comment: BMX is a different sort of biking, like [this](http://www.youtube.com/watch?v=pXSago8ijMo&feature=related). (Just asking for tagging purpposes.)
Comment: What if the car you want to leap is equipped with drum brakes and look shoes, instead of disk brakes and SPD shoes?
#humour
Answer: More useful for you would be going along to a basic aikido course, or if that's not available judo, gymnastics, ninjitsu or some other form that teaches you how to roll. Forget the holds and throws and just learn how to roll. When you can confidently run full speed at a waist-high obstacle and dive-roll over it, you'll be in a better position to survive a bicycle-enhanced version of that.
Find a grassy children's playground with a suitable step, bank or ditch, and practice going over the handlebars. As freheit suggested in comments, wear protective equipment. I suggest starting slowly and using an old BMX rather than a bike you care about. The bmx will be easier to get off as well as cheaper.
To be honest this isn't something I would practice. What I get people to do when I'm training them is just turning the bike to one side and fall away from it. At walking speed. The idea is just to convince them that they're not going to die if they fall off, and to give them a few tips on keeping their arms bent. Mostly I use it to sell them on the idea of cycling gloves (and not riding in crappy footwear). Note that I've only done this where helmets are mandatory, but otherwise I'd also be selling people on helmets.
Comment: Why gloves? The roll they taught me is over the outside of one hand, then the shoulder, then the ribs on the opposite side of the body, buttocks, feet. They made us hold things while rolling to explicitly not use our hands.


Why do satellite tracking programs have to be updated?

Question: So I've heard every once and a while you have to update your satellite tracking software because of the fact that the satellites are falling towards Earth. Why can't the program automatically calculate every factor in so it doesn't have to update it?
Comment: Isn't falling towards Earth half of the definition of orbiting? (the other half being falling in such a way that you don't hit the orbited body)
Comment: All the satellites are in free-fall.  They just keep missing.  8-)
Answer: There are at least 4 significant things that make satellites difficult to exactly determine:

The position and velocity of a satellite is only known at any one time with a finite precision. Without a perfect knowledge of where the satellite is and how fast it's moving, it's impossible to know where it will be in the future.
The atmosphere is quite uncertain, sometimes it will drag more, other times drag less. The amount depends on the amount of solar activity. Also, the drag depends on the orientation of the spacecraft, so an anomaly in the spacecraft pointing can cause problems in determining where it is.
There are complex gravitational factors that can influence where the spacecraft is. These are very difficult to program in.
Thrusting, either in the form of an active propulsion from the spacecraft, or being hit by space debris or other objects, can cause problems.

Bottom line, it's just a hard problem to figure out, and it's much easier to get periodic updates to the satellite positions. But if you can't get them for a while, you should be fine for a period of time, several weeks at least. If you can't get them in that period of time, then your best bet is to try listening for the W1AW broadcasts, which give out the amateur satellite element sets.
Answer: You must update the orbital elements that your satellite tracking software uses to predict the location of satellites in order to get continued accuracy in the predictions.  Sometimes the orbital elements are not known exactly for a new or relatively unimportant satellite.  More importantly, the orbital elements can and will change over time.  Low earth orbit satellites will slow down due to friction from the remnants of atmosphere at their altitude.  All satellites will have their orbits affected by the gravitational influence of other bodies.  Although the principal gravitational effects will be from the Earth, Moon and Sun, other objects will also influence the orbit.
Answer: Some of the factors, such as friction against the upper atmosphere, can have the same sort of predictive problems as with lower weather prediction (non-linear dynamical "chaos", or sensitivity to initial conditions that is well beneath measurement error).  A satellite in orbit is also part of an N-body system, which does not have a clean closed form trajectory solution.


Force every HTTPS to one url

Question: Is there a bug free way to redirect/forward all HTTPS requests which forwarding through a router to one url ?
I want to redirect all clients https to specific page something like hotspots walled garden .
I know that https is secure and we can not see inside of it . i want to redirect every https and there is no if/then statements in packet flow so maybe it will possible
Answer: You cannot, not without every browser giving huge red "certificate mismatch" alerts.

Force every HTTPS to one url


unable to bake runny batter recipes

Question: I made a chocolate cake and recipe calls for buttermilk and oil which makes the batter liquidy,but when I bake it, they turn out rubbery or they become very dense and when I press it feels like soft boiled chocolate paste like texture and also they crack on top, it only happens with the runny batter recipes and thick batter recipe cakes are perfect and super fluffy,what could be the problem?
Comment: How long did you mix it, and how long did the batter rest before you baked it?  Overdoing either one will develop gluten and could explain the 'rubbery' problem.  Using a higher protein flour than what the recipe writer used can cause the problem, too.
Comment: unvented oven? Wrong (eg single vs double acting baking powder, baking powder vs baking soda, carbonated vs plain water), defective (eg stale baking soda), or mishandled (eg added at the wrong time) raising agent? misunderstood and omitted recipe step or ingredient (eg an acidic ingredient that works with baking soda, an aeration technique)?
Comment: Edit your post to include an example of a recipe that didn't work out for you.
Comment: i just mixed dry and wet ingredients separately and then folded them together until everything is incorporated
Answer: I bake a lot with gluten free (I cater for a wheat allergy) and as a direct result a lot of my batters are runny but I still get a fluffy final cake. Bread doughs are more like batter than bread too.
You mention folding in the comments, which prompts me to wonder if you're making a red velvet cake, given the recipe points mentioned.
If that is the case, you need to aerate the egg whites separately, and fold them in last, taking care as to not lose the air you put in.
If you edit your post to include the recipe that would help with diagnosis a lot more.

unable to bake runny batter recipes


GWT hosted mode not working with Spring + Eclipse + GWT Eclipse plugin

Question: I've been trying to get GWT working with Spring for a while now. Is there anyone who is using official Eclipse GWT plugin with Spring, and who has managed to get hosted mode working with that combination?
I'm using GWTController to initialize GWT through dispatcher-servlet.xml. Since my WEB-INF is not in war, but in WebContent folder, I use "-war WebContent" switch when compiling Java code to .js.
As for hosted mode... if I try to run it through IDE (Run as Web Application) I get "Launch failed - Could not find any host pages in project MyProject." I tried running it with Ant task which goes something like this:
<condition property="XstartOnFirstThread" value="-XstartOnFirstThread">
    <os family="mac"/>
</condition>
<condition property="XstartOnFirstThread" value="">
    <not><os family="mac"/></not>
</condition>

<target name="hosted" depends="" description="Run hosted mode">
    <java failonerror="true" fork="true" classname="com.google.gwt.dev.HostedMode">
        <classpath>
            <pathelement location="src" />
            <path refid="my-client-classpath" />
        </classpath>
        <jvmarg value="-Xmx256M" />
        <jvmarg line="${XstartOnFirstThread}" />
        <arg value="-startupUrl" />
        <arg value="MyPage.html" />
        <arg value="my.gwt.client.Whatever" />
    </java>
</target>

This results in hosted mode starting, but I get 404 instead of my web page...
EDIT: When I go to hosted mode, I see folder with compiled Javascript code but nothing else. So my question is basically has someone got a good tutorial or a setup he can share? There is a lot of half-baked info on the Net, but I wasn't able to make any of it work.
EDIT 2: Here's my .gwt.xml file, it's pretty basic:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE module PUBLIC "-//Google Inc.//DTD Google Web Toolkit 1.7.1//EN" "http://google-web-toolkit.googlecode.com/svn/tags/1.7.1/distro-source/core/src/gwt-module.dtd">
<module rename-to='whatever'>

<inherits name='com.google.gwt.user.User' />

<inherits name='com.google.gwt.user.theme.standard.Standard' />

<entry-point class='my.gwt.client.Whatever' />

<extend-property name="locale" values="hr" />

</module>

Comment: Can you post the url that your browser tries to access?
Comment: URL is one of the arguments in Ant task - in this case "http://localhost:8080/MyPage.html", which works when I start Tomcat normally but doesn't work in hosted mode.
Comment: Can you post your module cfg? Are you using the rename-to attribute?
Comment: Miguel, I would, but sadly, I don't know what you're talking about. Are you referring to run configuration screen?
Comment: I'm referring to the file with the .gwt.xml extension.
Answer: We used this tutorial to get it working for us, hope it helps


How do I remove dust from fabric lampshades?

Question: Many of my lampshades are made of different types of fabric, which accumulate dust. I've tried wiping them, vacuuming, etc, but I haven't been happy with the results.
What can I do?
Answer: You can get a length of clear packing tape about 8-10" long and, holding the ends, press it against the lampshade and draw it back off. It will have picked up the dust in that area. Then press it on another spot. Repeat this process until the lampshade is clean.
Unless it's very dusty, the tape usually lasts a good 2-3 shades for me. Once it is no longer sticky enough for use I cut another piece.
Answer: Similar to your suggestion of tape, but probably easier and quicker is to use a lint roller like this:

A lint roller has a roll of masking tape on it, and is usually used to remove lint from clothes.  But you could also use it to remove dust from lampshades.  Just roll it on the lampshade and it will pick up the dust.  Then after the tape loses its stickiness, just tear off that piece (they are pre-cut into squares on the roll) and it will be ready to pick up lint/dust again.
Answer: The brush-end of a vacuum's upholstery cleaning attachment works great.
Attach it to the hose (and extension, if necessary) then starting at the top of the shade, use straight, gentle stroke all the way to the bottom rim.
Turn the shade a tiny amount -- or move your body around it -- then repeat in slightly overlapping swaths until you've completed the entire diameter.
Answer: Lampshades are very difficult to dust. They contain nooks and crannies which make it impossible to really get in there and clean them thoroughly. They are also fragile, so you can't wash them off using water, detergents, etc. Most vacuum cleaners would also damage them unless you have a soft brush attachment.
One of the best ways to dust them is to use a can of compressed air. This is the same kind of compressed air used to clean out electronics, and most office supply stores carry them. Work back and forth, and up and down across the entire shade and make a couple of passes. This should remove the vast majority of dust.
Answer: This may seem like an "old-fashioned" solution, but have you tried a simple feather duster?  I have a cheap one like this, and find it excellent for getting dust off lampshades.
Of course, the feather duster will mostly just scatter the dust into the air, so you may want to hold a vacuum cleaner nozzle nearby to collect it.  Or just let it settle, and then vacuum the floor.


How can I check if I messed up my encrypted Swap configuration?

Question: on my machine running 11.04, I somehow managed to remove the partition which was used as swap, while I was repartitioning the hard drive. I then turned off swap and tried to reconfigure it with a different partition. (I had wanted to do that anyway.) "/etc/fstab" contained the following line:
/dev/mapper/cryptswap1 none swap sw 0 0

Looking at "/etc/crypttab", I found a reference to the old swap partition, sda7:
cryptswap1 /dev/sda7 /dev/urandom swap,cipher=aes-cbc-essiv:sha256

I changed the line to use the new partition /dev/sda2, which I had formatted as swap:
cryptswap1 /dev/sda2 /dev/urandom swap,cipher=aes-cbc-essiv:sha256

I then turned swap back on, and it seems to work. "free -m" now tells me I have the 4 GB free swap space available in the partition, even after restarting.
However, I am a little suspicious that it should be so easy to just rewire swap through one little file entry. Also, the Disk Utility does not show the partition as being used as swap; it says "Usage: -".
Have I missed something? Are there other or additional steps I should follow to properly reconfigure the swap partition?
Answer: If /dev/sda2 has been properly formatted as swap, that change should be all that is needed. If free -m and swapon -s report the swap partition you can assume it is working.


If I use a normal build of ffmpeg how take advantage of video acceleration for scale?

Question: I generally use ffmpeg for encode in h264 and also resize media
My common command is something like:
ffmpeg -i in.mov -c:v libx264 -preset ultrafast -b:v 5000k -s:v 1280x720 out.mov

I have an Nvidia GeForce 1060 card.
I also use the Zeranoe Builds or various generated with the crosscompile scripts (but i'm not very pro with it)
What i would like to know is:
1) It is possible to SCALE for example from 4k or FHD (1080p) to HD (720p) by taking advantage of GPU acceleration instead of using the normal SCALE ? It is possible also to specify if use bicubic, bilinear and so on?
2) It is possible to encode in h264 faster by taking advantage of GPU acceleration ?
And what syntax/options to specify in ffmpeg to do so.
Thanks in advance.
Answer: The answer to your second question is yes. Change -c:v libx264 to -c:v h264_nvenc.  I use those builds as well.  If you use the option -encoders you can see a list of included video and audio codecs.
This is a good resource for encoding with FFMPEG.
See the warning on this question if you try this


Havdalah and fingers

Question: As the berachah on the havdalah candle is made, I've been told, the proper thing to do is to raise your hands toward the candle with your fingers curled over your palm and look at the shadow of your fingers, which are cast onto the palm. Where is the halachic source for this?
Comment: http://www.rabbisedley.com/halacha/shabpos/Havdala1.pdf
Answer: First of all, the specific language of what you've heard, that "as the berachah on the havdalah candle is made..." is not necessarily correct; either the bracha should be before the checking, or the fingernail-checking should be done before the blessing, but not at the same time. (As to which one comes first: R. Moshe Feinstein, in Igros Moshe O.C. 5:9 writes that the correct custom is to make the blessing first, and only then look at your fingernails, but the Mishna Berura says that it is more correct to do the opposite, to look, then bless).
The Mishnah in Berachos 51b writes the blessing of "Bore Moerei Ha'esh" should only be made if one benefits from the light of the candle. The Gemara later on daf 53b writes that (according to the accepted opinion) this means that one has to get enough use out of the light as to differentiate between two coins: a sela and a pundyon (these two coins are actually very similar looking to each other).
Since we don't usually have coins on us at the end of Shabbos, the Tur (O.C. 298) writes that instead one should use the light to differentiate between their fingers and fingernails. (The Gr"a to Shulchan Aruch provides an earlier midrash as the source). Besides for this halakhic reason, the Tur gives other reasons as well: nails are a symbol for growth and proliferation, because the fingernails grow. (Many quote other mystical reasons as well).
Comment: @DanF that's a separate question, but a good one. You should ask it
Comment: @Matt - "The Mishnah in Berachos 51b writes that one should not make the blessing of "Bore Moerei Ha'esh" should only be made if one benefits from the light of the candle". So, if there is so much electrical lighting in my home or shul, do I need to turn off all the lights? In my shul, they turn off most of them. But not everyone does this.
Comment: You're getting "revenge", aren't you :-) :-)
Comment: @DanF :-) I meant it in all honesty though really
Answer: There are some interesting aggadic sources to specifically look at your nails:
1) We are asking for the week to be fruitful and multiply- like nails, that continually grow (mentioned above).
2) That the fire created after shabbos came out of the fingernails of Adam. (Kol Bo 41)
3) In בפרקי דר״א פי״ד, it says that Adam's clothes were made of nail like materials. After the sin, his clothing fell away and he realized he was naked. This explains Hashem asking Adam "who told you that you were naked ? did you eat from that tree ?" Showing the connection.

Havdalah and fingers


Can non-intelligent life naturally evolve the ability to space travel and to live in interplanetary space?

Question: Can non-intelligent life forms evolve to leave their home planet and travel in interplanetary space, for instance, grow on atmosphereless icy moons and transfere spores over interplanetary space?
Comment: All I can say is that such a species is one hardy sonofagun! I mean, it must be harder to get rid of them than it is to get rid of roaches.
Comment: I get the feeling this question has been asked before, but all I can find is [this question](http://worldbuilding.stackexchange.com/questions/20615/how-would-a-massive-space-creature-evolve) and those linked to it. They should have all the information you need, though it may take some digging.
Comment: I imagine so, as long as the science you follow isn't too "hard" ... Flies can apparently be brought back to life if frozen quickly and then thawed. Your spores could use this method to survive in space. Perhaps the icy moons have frozen or liquid oxygen on them and come from a densely packed asteroid field type setup (making jumping from rock to rock a possibility or even a necessity) though it's difficult to see how the creatures could raise their temperature enough to make the chemical reactions necessary for life.
Comment: Does [panspermia](https://en.wikipedia.org/wiki/Panspermia) count?
Comment: [Elder Ones](https://en.wikipedia.org/wiki/Unspeakable_Vault_(of_Doom)) servants?
Comment: Zergs. Complete with the spores question.
Comment: Logically, most vacuum-based ecosystems should be located in areas with an abundance of resources, such as interstellar gas clouds and the rings of gas giants. The real barrier is that such creatures would need a drastically different method of synthesis/respiration since they live in a vacuum.
Answer: Yes, via panspermia.
Panspermia is the idea that extremophiles "hitch a lift", as it were, on ejecta from collisions between celestial bodies. There are a few obstacles, because the microbes would have to survive all three phases of travel:

Launch (as well as the impact event)
Travel in the harsh environment of space
Atmospheric entry and landing, with high temperatures

Extremophiles are really the only types of organisms that could survive such a journey. More complicated organisms (with more needs) would surely die en route.
On Earth, here have been some discoveries of materials related to organic matter that might be evidence of panspermia; see Bell et al. (2015) for one example.

Image courtesy of Wikipedia user Beao under the Creative Commons Attribution-Share Alike 3.0 Unported license.
Answer: Yes, but.
Yes it can be done but I would list a few caveats.

Odds are the natural selection process is not going to select for surviving in space...why would it.  Natural selection selects the individuals most fit in their respective environments.  This simply means that if an organism makes it to space accidentally survival will also be random/accidental.
The more complicated the creature the less likely they are to pull this off.  The more biologically complicated you become the more you are tied to your environment, mainly because you need more quantity and variety of resources.

The most likely scenario in my mind is a single celled organism.  The organism would be launched into space via natural phenomenon, to be trendy lets go with the ejection of water from a nice little moon called Enceladus.  If there are single celled organisms in the theoretical oceans on the moon, the plumes of water vapor could contain little critters.
Over time some could randomly have the ability to survive in space by essentially being dormant while they travel.  Say they land on an asteroid or another moon that has the simple resources they need to survive...a particular mineral maybe and viola, you have your space faring critters.
Comment: The creatures that made it from ocean to the land were quite complicated. The creatures that evolved ability to fly were also complicated.
Comment: @Anixx but have the same resources available to them (albeit in different forms) where-as going to space requires you be able handle a complete lack of resources.  The more complicated you are the harder it is to cope with virtually 0 resources
Comment: I think you're missing something about natural selection, nature doesn't select the fittest, the fittest are retrospectively termed such simply because they survived..whatever the rest didn't.
Answer: If there was a low gravity moon with an atmosphere but in which its tallest mountains were so high that their tips were to stick out above the atmosphere then that could potentially lead to some life evolving to survive in the vacuum of space.  Because the transition from atmosphere to vacuum on the mountains could be very gradual individuals that don't travel very far from where they started life might live with basically the same amount of atmospheric pressure as their parents.
Over many generations populations could migrate however from regions with normal pressure on the ground to the peaks of the mountains that would be in a vacuum.  As populations migrate up the mountains their skin and the openings to their bodily holes could become more and more pressurized to hold in their bodily fluids.  Plants could also evolve to become more and more and more pressurized as they migrate up the mountains.  Animals that fly would at first evolve more and more powerful wings as they migrate up the mountains but would eventually evolve to have smaller and smaller wings as wings become useless in a vacuum.  Animals and plants living at higher and higher elevations might start to evolve to extract more and more energy from chemicals in the ground as it would be inefficient to extract energy from the air.
Animals and plants on the peaks of the mountains would tend to evolve skin that protects their insides from deadly radiation considering that they would have no atmosphere to protect them.  If there was ice at the peaks of the mountains life on the peaks of the mountains could use that as a source of hydration considering that water could not exist as a liquid in a vacuum.
If some animals that live on the peaks of mountains use chemical defenses that involve chemical reactions that could end up getting modified into a means of locomotion as they could eject fuel out of their backsides in order to move.  Animals that evolve this means of locomotion could diversify the fastest out of the animals living in a vacuum as they would tend to be able to travel the furthest the fastest.  If the planet had multiple mountains that stick out above the atmosphere then animals that can move by ejecting fuel out of their back sides that evolve on the peak of one mountain could migrate to the peak of another mountain.
If some of the animals were able to move fast enough using chemical propulsion they could escape their moons gravity and travel to other moons including ones that have no atmosphere as they would have evolved to live without atmosphere.  Some of them could carry the seeds of plants as well as having smaller animals that can't use chemical propulsion hitch a ride on them so that they spread other animals and plants with them meaning that they moon hop in the same way that some animals and plants island hop on Earth.  These types of animals would be the most diverse as they would be able to spread to moons that have no atmosphere where life could never have started.
Some could perhaps evolve to eat parts of their gas giants rings so that they could get nutrients on journeys between moons.  Some species could perhaps even evolve to subsist entirely on space junk and they could perhaps live entirely in space between moons and eventually between planets.  Species that live between moons and planets could get very large as they wouldn't have to fight against gravity in the same way as animals on the surface of a planet and being very big could allow them to go longer without eating.  Being very large would also allow for larger eyes that would be better at detecting food from large distances as in distances potentially larger than the radius of a moon.
Answer: There is no known reason to believe there is any limitation on what can evolve, simply because we do not understand the process to assign limits, so the answer almost has to be a default "yes."
Escaping a gravity well is very tricky, requiring a lot of energy, but if there was a reason, there might be a species that figures out how to use things like winds, solar energy, and possibly a small packet of chemical energy to try to escape.  I don't think it's likely (as in it'd be a miracle if it happened), but there's nothing in the laws of physics that forbids it.
Waterbears are known to be able to survive the rigors of a deep vacuum, so we know its possible for organics to function in extremely inhospitable worlds.
That all being said, when it comes to world building, we must always remember Sanderson's First Rule of Magic:

An author's ability to resolve conflict using magic is directly proportional to the reader's ability to understand it.

This rule goes not only for high-fantasy magic, but science fiction magics as well.  This species is highly "exotic," as in a real scientist would scoff at the possibility (but "can" is such a great open-ended word in a question!).  You would have to make sure you don't resolve to much conflict with it unless you fleshed out why such an astonishingly unique species came into being.
Comment: Beat me to it. I was about to post an answer that opened with the line "If there is sufficient pressure to do something and it's not actually against the laws of physics, evolution can find a way to do it."
Comment: Chemistry says there are limits on what can evolve naturally, being as some things simply cannot occur naturally in sufficient quantity to result in 'organic' incorporation.
Answer: There are three main routes to natural evolution into space-going life:

Panspermia is covered in other answers.  I think that this is cheating though, as panspermia is planet-based life that travels through space in an inert form and then resumes life on a new planet.  I don't consider it to be life in space, as it's not really alive in space.
Life could develop on planets and then evolve into something that can live in space.  Note that this works best if there is a lot of life somewhere that is becoming progressively more like space.  It needs to be a lot of life because space kills life optimized for planets.  We need enough base material to leave room for natural selection.  It needs to happen over a long period of time so that new generations can build life for the new circumstances.  Note that panspermia may be a stage in this.
It is conceivable that life might find moments on comets or in a sufficiently soupy region of a nebula to develop in space.  Maybe when we explore enough we'll find some.  Note that there is Earth-based life in extreme conditions like volcanoes.  Perhaps an environment like Saturn's rings could hold life.  It seems like it would take a really long time to develop though.  Realize that we think that what we now call one-celled life developed from even smaller life (e.g. we think that mitochondria might have started outside cells).  Given how vast space is, it might be difficult for the life to encounter enough additional life to even get as far as one-celled life.  It might still be stuck at the prokaryote stage or even the protocell stage.  Realize that it took something like 3.5 billion years for the first animal life to develop on Earth.  This route may be slower than that.

I'm assuming that what you want is to eventually get to a form of life that can reproduce in space.  Perhaps you even want a form of life that can travel in space willfully.  So a space plant that floats through a nebula collecting materials may not count.
It seems at least potentially possible.  We really haven't traveled far enough to disprove the existence of such life.  Is there life on Mercury?  Or the sun?  We don't know.  We haven't found life on Mars, but that merely suggests that it is difficult.
I think that a form of life that travels via a solar sail, collecting material as it goes would be possible.  I think that an intelligent race could create some.  Since the universe is a big place, it should be possible for randomness to duplicate that feat -- somewhere.
Comment: In some ways a low energy & homogeneous environment might actually be preferable to 'goldilocks' planets. Compounds stable 'under their own power' in such  an environment have much less to fear from the random act of destruction 'angle' as in highly variable and chemically violent planetary environments. Cellular life is essentially just 'one' molecule folding another molecule around itself in such a way as to prefer for integrity of the original, and this happens in nature in many variations...whilst it's hard to imagine, there is the possibility of complex massive single molecules life.
Answer: some bacteria survives in space:
http://www.panspermia.org/bacteria.htm
They could be launched into space when their planet is smashed into fragments by an astroid.
You can't get much more unintelligent than that.
Comment: Two things. 1) *some bacteria survives in space.* - Source, please. I've heard something like that, too, but it would be nice to have a reference that backs it up. 2) This assumes that the bacteria are already in space, which the question does not. It asks about *getting* to space, too.
Comment: Thanks for adding the source. Post-edit, though, it seems pretty much the same as [my answer](http://worldbuilding.stackexchange.com/a/28670/627).
Comment: A way to survive in space would be to be embedded in rock (thus safe from radiation, with material such as sulfides or carbon compounds to metabolize.  There are some tough rock-dwelling [microbes](http://www.livescience.com/29857-microbes-discovered-in-earths-crust.html) that might be ejected in a meteor strike or some such.  They might be able to colonize other rocky planets.
Answer: Well, you said 'non-intelligent' but if we loosen the definition a bit I see an interesting option.
How about custom made 'Pets' modified to live in space by an intelligent species. Think something like flying cats or dogs with large solar energy gathering 'wings', GMed to thrive in vacuum and naturally extract organics from rocks and space debris.  'Built' to aid in asteroid mining but then abandoned or escaped and gone wild. Perhaps very long lived and with 'natural' solar sails or other propulsion systems. Migrating back and forth from comets and small moons.
Perhaps with enough time, they might evolve into a complex biome with multiple competing species.


Difference between PyPy and JVM

Question: From my understanding the default Python interpreter(CPython) compiles source code into bytecode and then interprets the bytecode into machine code. PyPy on the other hand makes use of JIT to optimize often interpreted bytecode into compiled machine code. How is this different then the JVM? The JVM is an interpreter + compiler. It compiles source code to bytecode and then optimizes the often interpreted bytecode into compiled machine code. Is there any other difference?
Comment: The bytecode and the underlying abstract VM are widely different.
Comment: So the concept is the same but the implementation is different?
Answer: There are two major differences between the two.
First: the JVM is abstract, PyPy is concrete. The JVM is a specification, a piece of paper. PyPy is an implementation, a piece of code.
There are many different implementations of the JVM which work very differently. Some only interpret the JVM byte code, some only compile it statically ahead-of-time, some only compile it dynamically just-in-time, some have both an interpreter and a JIT compiler, some have an interpreter and multiple JIT compilers, some have no interpreter and only one JIT compiler, some have no interpreter and multiple JIT compilers. Some have tracing JITs, some have method-at-a-time JITs, some have both. Some have native threads, some have green threads. Some have tracing garbage collectors, some have reference counting garbage collectors. And so on and so forth.
Second: PyPy is more general. It is not an implementation of a specific language, it is a framework for easily creating efficient language implementations. There are a lot of different language implementations built using the PyPy framework, there's Topaz (an implementation of Ruby), HippyVM (an implementation of PHP), Pyrolog (Prolog), RSqueak (a Squeak VM), PyGirl (a GameBoy emulator), langjs (JavaScript), and also implementations of Io and Scheme. And of course also an implementation of Python.
Since you asked specifically about the compilers, there is a very important distinction between PyPy's JIT and the JIT compilers of other mixed-mode engines. In a typical mixed-mode engine (e.g. Oracle HotSpot JVM, IBM J9 JVM, Rubinius, Apple Squirrelfish FX, …), the interpreter and the compiler run side-by-side and process the same program. The interpreter starts off, interpreting the program, and once it has been determined that it would be beneficial to compile (parts of) the program, the program gets handed off to the compiler and compiled.
In PyPy, however, the compiler doesn't compile the program that is interpreted by the interpreter. It compiles the interpreter itself as it is interpreting the program!
Now, why would you do something like this? Think about what this means: if you JIT compile the interpreter while it is interpreting the program, what you end up with, is a specialized version of the interpreter which can only interpret that one program, all together compiled to native code. But, an interpreter which can only interpret one single program is indistinguishable from that program. So, in other words, you have just compiled that program without even knowing anything about that program!
This has to do with PyPy being intended as a framework: this way, you only need one JIT compiler and it works for all languages! The only thing you have to write if you want to implement a new language in the PyPy framework, is the interpreter. You get the JIT compiler "for free". And the interpreter can be very simple, it doesn't have to perform any aggressive optimizations or so, because the JIT compiler is quite good. (For example, HippyVM, the PHP implementation using PyPy, is almost 8 times faster than the Zend Engine (the standard PHP implementation) and twice as fast as Facebook's aggressively optimized high-performance PHP implementation HHVM.)
Comment: ain't VM being abstract and JVM concrete. JVM sounds very concrete to me, a virtual machine that interprets Java bytecode. Yes, there are different JVM implementations, but still it doesn't make it less concrete, does it?
Comment: When you are talking about PyPy compiling the interpreter itself you are talking about the idea of partial evaluation right? and links or references?
Comment: @denis631: The JVM is a piece of paper that first needs to be turned into a piece of software in order to do anything useful. The PyPy VM is a piece of software already, so it is one step more concrete than the JVM.
Comment: @denis631: PyPy originally intended to do partial evaluation, and I believe there are papers about that. But, they went away from partial evaluation and used this idea of the meta-tracing JIT instead, i.e. a tracing JIT that does not trace the user code, but the interpreter that is interpreting the user code. There is a nice retrospective about the history of PyPy on the PyPy blog which discusses this. Most PyPy-related papers are also linked somewhere on the PyPy website.
Answer: The concept is only similar in the broadest strokes. Yes, both interprets a simplified program representation called bytecode and compile parts of that to optimized machine code, but that's there is stops. For starters, "JVM" is a catch-all term for all implementations of a standard. There is only one PyPy. There is no one JVM.
In addition, the compilation is done rather differently. Most JVMs are so-called method JIT compilers, that is they compile and optimize individual methods (modulo inlining). PyPy is a so-called tracing JIT, it compiles a part of the dynamic execution of the program, i.e., it follows the control flow wherever it takes us, be it through fifty different methods or covering only one small part of a larger method.
Comment: Another, even more important difference, is that most JVMs (maybe with the exception of Maxine) JIT compile the *user program*, whereas PyPy JIT compiles *the interpreter* while it interprets the user program. That's how PyPy can have a JIT compiler for all languages without having to write a JIT compiler.

Difference between PyPy and JVM