Is it secure to collect common public addresses under a wallet using BlockCypher Wallet API

Question: I am working on an exchange platform with users having separate pair of public and private keys using blockcypher api. I encountered Blockcypher Wallet API, and it seems its a pleasant way of collating Set of Public Addresses to Query Together. For some reasons, i intend to add all new generated public addresses created by any user under a single wallet name (the site name) using the "Wallet API", this will come in handy in the case where by i need to filter all incoming transactions webhook to only the public addresses under the site name into a callback url. So i needed to confirm if this is a secure way to handle it. I would appreciate if an elegant way to handle this can be suggested.
Comment: If you're building an exchange, and want 'a secure way to handle things', you should consider running your own node, not trusting a third party.
Answer: When using a third party, you will be trusting them to give you correct information. This is not just about being dishonest but also about not having bugs.
For instance consider the recent cve-2010-5141 vulnerability. If you are running a full node on your own, you can know what is going on and you can upgrade when you find out about it. But if you rely on a third party you have to trust that they upgrade and are aware of it.
As a matter of fact they apparently have not yet upgraded and on TestNet they are showing a block with exploiting transaction as valid. So theoretically you, as an exchange, can lose money if you were relying on them and if this was MainNet.


My phone tile is missing.

Question: The phone tile is no longer in the front screen or the app list. where has it gone?  i'm using a 650 lumia on windows 10. this obviously means i cant make calls unless they are in my contacts list.
Comment: one of my friend got the same problem in his 630, he couldnt pin sim2 phone tile. he had to do hard reset. he was on 10586.494 when this problem occurred.
Answer: If a tile gets unpinned from the start screen, that doesn't mean its uninstalled from the phone.. It's simply removed from the start menu of the phone.
Follow the following steps to get it back to the start screen:

Unlock your phone, and whilst on the start screen, swipe from the right of the screen to the left.
Click on the search field and type in Phone.
Long press on the Phone app icon, and an option to "Pin to Start", will show..and, voila, you have the phone app back on your
  start screen.
Comment: Kevin said that the tile is no longer available in the apps list. `The phone tile is no longer in the front screen or the app list.` Can an app appear in search results although it is unavailable in the apps list?

My phone tile is missing.


Maggidim (angelic mentors) in Jewish history. How new is it?

Question: Did the phenomenon of "maggidim" (celestial/angelic mentors) who come to teach a person kabbalistic mysteries and other revelations, but begin with those who studied Lurianic kaballah in the 1500's - 1600's or was it always a part of Jewish history after prophecy ended? We have written records of many kabbalists in the 1500's - 1600's and on,being visited by maggidim such as Rav Yosef Karo of Maggid Meisharim fame and the lesser known Rav Shimshon Pesach of Ostropol as well as many others. Was that the beginning of this phenomenon?
Comment: Lurianic Kabbalah in general, and the legend of R. Karo, for example, stem from the 1500's; not the 1600's.
Comment: Note that the authorship of the Maggid Mesharim is a matter of dispute: http://judaism.stackexchange.com/q/56940/8775.
Comment: See Peninnah Schram's [Tales of Elijah the Prophet p. xxv](https://books.google.com/books?id=4hcmAgAAQBAJ&pg=PR25&lpg=PR25&dq=gemara+giluy+eliyahu&source=bl&ots=9Y_IXusHCN&sig=5AIPNWtoT9-WrBL7iwO4PuoF2Po&hl=en&sa=X&ved=0ahUKEwjliYa97bbRAhUCziYKHdn_AJ4Q6AEIGjAA#v=onepage&q=gemara%20giluy%20eliyahu&f=false) that this idea; specifically with Elijah is from the Talmudic period, and especially the medieval period.
Comment: @mevaqesh. I was thinking more in terms of these personal "maggidim" that many had and not the generic Eliyahu that we're familiar with.
Comment: Why do you assume that the maggidim from different stories were personal? Maybe they were the same character sharing revelations with multiple figured? Regardless, consider editing clarifications into the question itself. | Note that if you add that the angelic figures must be "personal", then I suspect that this would become nearly impossible to demonstrate, and hence answer.
Comment: Consider marking an answer correct.
Answer: The idea of celestial/angelic mentors beings revealing esoteric knowledge goes back to the Talmud and did not start in the 16th century. For example, Elijah reveals esoteric knowledge. In Talmud, Elijah appears as a supernatural being, associated with other angels. See for example Berakhot 4b:

It was taught in a Tosefta: Michael, as stated above, in one flight; Gabriel, in two flights; Elijah, in four flights; and the Angel of Death, in eight flights. (Sefaria).

Fairly early sources such as Pirkei D'rabbi Eliezer (ch. 28) also refer to Elijah as "the angel of the covenant":

שנקרא אליהו ז"ל מלאך הברית

In Ta'anit (22a) Elijah reveals which people will merit entry to olam haba.

ר' ברוקא חוזאה הוה שכיח בשוקא דבי לפט הוה שכיח אליהו גביה א"ל איכא בהאי שוקא בר עלמא דאתי א"ל לא אדהכי והכי חזא לההוא גברא דהוה סיים מסאני אוכמי ולא רמי חוטא דתכלתא בגלימיה א"ל האי בר עלמא דאתי הוא
Rabbi Beroka Ḥoza'a was often found in the market of Bei Lefet, and Elijah the Prophet would often appear to him. Once Rabbi Beroka said to Elijah: Of all the people who come here, is there anyone in this market worthy of the World-to-Come? He said to him: No. In the meantime, Rabbi Beroka saw a man who was wearing black shoes, contrary to Jewish custom, and who did not place the sky-blue, dyed thread of ritual fringes on his garment. Elijah said to Rabbi Beroka: That man is worthy of the World-to-Come. (Translation from Sefaria).

Yoma (19b-20a) similarly describes Elijah transmitting esoteric information:

דא"ל אליהו לרב יהודה אחוה דרב סלא חסידא אמריתו אמאי לא אתי משיח והא האידנא יומא דכיפורי הוא ואבעול כמה בתולתא בנהרדעא אמר ליה הקב"ה מאי אמר אמר ליה (בראשית ד, ז) לפתח חטאת רובץ ושטן מאי אמר א"ל שטן ביומא דכיפורי לית ליה רשותא לאסטוני
Elijah the Prophet said to Rav Yehuda, brother of Rav Salla Ḥasida: You have said and wondered: Why has the Messiah not come? Why is that surprising? Isn't today Yom Kippur, and relations were had with several virgins in Neharde'a, as the men and women stayed awake all night and that led to promiscuity? Rav Yehuda said to him: What did the Holy One, Blessed be He, say about those sins committed by the Jewish people? He said: This is what God said: "Sin lies in waiting at the door" (Genesis 4:7), and it is no wonder that men sin. He asked him: And what did Satan the prosecutor say about their sinning? Elijah said to him: Satan, on Yom Kippur, has no license to prosecute (Trans. Sefaria).
Comment: Got something against the Talmud commentless downvoter?


Samsung Kies 1.5 not connecting the galaxy fit device

Question: I have Samsung Galaxy fit with android 2.2 I have installed Samsung Kies 1.5 since I want to use mobile internet on desktop PC having Windows XP through USB. But when I connect my phone to PC using  data cable Kies keeps on showinf the message 'Connecting the device Please wait' for long time but it never connects. I have installed USB drivers for galaxy fit and I hope there is no prob with that part. Also USB debugging on the device is on. Can anybody help me out of this?
Answer: If you're planning to use Kies to connect to the device, USB Debugging must be off and the phone's USB mode must be set to Samsung Kies, otherwise Kies won't detect the phone.
Comment: Thanks for your response! But sorry I was wrong in stating my question. The device is getting connected when the USB debugging is off. But how to proceed for tethering? When I tick USB tethering on phone, Kies starts connecting the device again for long time and then no response. Do I also need to tick on Mobile AP option on the device? When I did it, its giving error. Now can you please help me on this?
Comment: I don't have that version combination for testing (running Android 2.3.3 and Win7), but for me tethering works then USB Debugging is on, I plug the device in and then tick USB Tethering. This automatically tethers the devices without the use of Kies. Does this work for you?
Comment: Oh, and you probably need this driver: http://www.google.com/support/mobile/bin/answer.py?hl=en&answer=182134
Comment: @ onik oh, It really works without using kies. :) Thanks a lot!


Is normalization process needed?

Question: Well after learning DBMS as a subject i got so many questions in mind. Normalization is one of them. As i learnt it there was a lot more confusion and i found that whatever we do in normalization process we can do it by general common sense also. Even while making projects also people are not used to follow it. So is it really needed? Is it followed in the companies? I am asking this question because probably it might consume more time to normalize the database. We can directly normalize it using just common sense therefore i don't think there is any need of following the standard normalization procedure. Correct me if i am wrong.
Answer: To answer your question, yes normalization is needed.
Common sense is a relative term and is open to interpretation.  RDBMS's have been around since the 1970's.  Normalization has been put into use on countless projects over the past 30 years, much to the benefit of the applications being developed.
The most complex time-consuming problems I have worked on in the past 15 years can be directly attributed to the database designer's lack of understanding (or willful ignorance of) the rules of normalization.
If you don't have the time to design a database properly, then you are in the wrong field, or are working on a project that is doomed to failure.
Answer: Every rule, every process, every pattern that is taught in programming courses is an effort to try to "institutionalize" common sense.  If all of your developers have perfect common sense at all times and are clear-headed and insightful, then you don't need to follow anybody's rules, processes or patterns.
However, as the saying goes: "Common sense ain't" - Meaning that people in fact often don't have perfect common sense and won't naturally do everything that they need to do to keep themselves out of trouble both now, and even more especially into the future.
Normalizing your database is very much a common practice in organizations with professional data modellers and developers who understand the importance of getting your database schema right.  It does not take a lot of time to normalize your database.  In fact, most experienced data modellers do it naturally as they build out their models while they're still in the whiteboard phase.
Taking the (very little) time it takes to ensure that your logical schema is normalized before you start building, and taking the time to understand precisely why you are denormalizing in your physical schema, and what the impact of that redundancy will be on your code and business is an important part of a professional development process.
Answer:
The point is, however, that the principles of normalization take those
  common sense ideas and provide a precise, accurate characterization of
  those intuitive concepts.

Chris Date and David McGoveran on The Principle of Orthogonal Design.
Answer: Normalization may be mostly common sense but it is "formalized common sense" (Chris Date). Perhaps the examples you studied at college were quite simple and easy to resolve in your head without careful application of logical methods. In practice not all data models are that simple. Having a precise way to analyse, understand and resolve complex problems is important once you get beyond a tutorial.
Answer: To answer your questions:  If you can live with the consequences it really isn't needed.  Yes, it is used by all the companies I have worked with.
Common sense can get you only so far.  In some cases common sense is just plain wrong.  Many of the design problems I have seen have been a result of giving in to common sense.
Common sense tells you social insurance numbers are a unique identifier.  Besides the legal issues of using them as such, this fails on at least four counts:

Most countries began issuing the numbers before they had the appropriate automated systems.  In some cases more than one person was issued the same number.
Some people may apply for and get issued more than one number.
More than one country issues social insurance numbers.
Not everyone has a social insurance number.

Data normalization is a different skill set than application design.  Data base design deals with data at rest, as opposed to application design which deals with data in motion.  Key values are critical to database design, while an application may function perfectly well without them.
Like many good practices it is a case of pay me now or pay me later.  You can spend some time now normalizing you design, or spend lots of time later fixing you design.  However you do the design, it may not be a perfect model for your needs.  It is easier to add appropriate de-normalizations later with a full understanding of the risks and costs, than to remove unintended de-normalizations later.
Some of the things you should consider.

Is the candidate key stable over time?  If you allow the user to create it, it likely isn't.
Should you use a surrogate key for this table?
Besides the primary key are there other unique keys?
Is the candidate key truly unique?
Are the attributes truly dependent on the primary key?
Are any attributes derivable from other data we have?  If so, they are a de-normalization.  Consider deriving them initially and de-normalizing later if necessary.
Are all the attributes of the table part of the same concept?  If not, split them conceptually, and consider how you want to do the physical model.

Once you have a normalized conceptual model you should consider whether this will be your physical model.  You should be close and some companies don't bother with a formal transformation step.  In other cases, the model may need significant transformation.   In some cases, you may relax the rules for an entity.  In others you may combine entities.  Some cases like subtypes have alternatives for implementation.  A bit of consideration at the beginning can save a lot of rework later.
If you have input from the business be sure you understand what they are talking about.  I have seen the same term used to refer to three entirely different things.  In others the differences may be subtle, and might be important.
Answer: To correct one common but important misconception: You don't "normalise a database", you normalise a Logical data model.
Data design, the process of designing how your data will live at rest, has four distinct phases: Conceptual, Logical, Implementation, Physical.
Normalisation is the process of refining the Logical model. Is it required? Yes, if you want your Implementation and Physical models to protect data integrity and to perform well.
Tactics that protect integrity can reduce performance so sometimes the normalisation process applied to the Logical model is reversed in the Implementation and Physical models, a process usually called denormalistion. This is a tradeoff - denormalisation means accepting less data integrity protection in the name of better performance.
(This also means that questions posted here of the form "is this table normalised?" are meaningless unless the poster includes the conceptual and logical models from which the table was derived.)
I suspect the OPs situation is that they learned "a database system" rather than learning "data design". I often see this in people who learned Microsoft Access. They come to believe that the database (the physical model) is the whole data model.

"Normal Forms: Dependent on Dependencies", Fabian Pascal.
"Data Warehouses and the Logical-Physical Confusion", Fabian Pascal.
"Pro SQL Server 2005 Database Design and Optimization", Louis Davidson et al.
"Database Design for Mere Mortals: A Hands-On Guide to Relational Database Design", Michael J. Hernandez.
Comment: Perhaps it would be better to say that we should normalize the *logical structure* of the database. The phrase "logical model" is often (mis)understood to mean merely a preliminary design for a database rather than something actually existing in a database system. The important point surely is that what you *implement* ought to be normalized, not just what you sketch on paper :)

Is normalization process needed?


Are Continuation Patents only available for patents filed in the USA and Australia?

Question: Regarding Continuations Patents and all questions related to them and the work that is being undertaken for creating a Wiki on this subject, please can it be made clear in the Wiki and at the top of all the question and answer streams relating to this subject that Continuation Patents are unique to the USA and Australia and are not found anywhere else or available to any other country.This is not the case with Divisional Patents which are universally available throughout the PCT. Continuation Patents for patents granted in the USA only are of course open to all national based patents that file in the USA also, so it is difficult to claim that this system does not produce a level plying field for all but it does need to be clearly understood.
Comment: I am not aware of divisional patents available through the PCT route. Does anyone else have a clue about that? If not, then perhaps this question should be edited.
Comment: @chempatent1981 There's definitely no PCT divisional. But I don't think you can read too much into the question, it doesn't make any sense to me.
Answer: I was quite unclear on what was being asked here, so I moved your question to Ask Patents Meta in the hope that I could give something of an answer, a site for asking questions and making suggestions about the site itself.
If you'd like to modify any content you see on the site (questions, answers, tag wikis, etc.), you're free to use the "edit" link below them. At that time, your suggestions will be placed in a queue for review by other users of the site before being published for everyone to see.
On the other hand, if you're concerned with modifying off-site material, could you please clarify what that would be?


Is it safe to use swing-tops?

Question: I just started brewing my first batch (yay!) and want to set up for bottling while I wait.  My question is simple: Can I start using Swing-Tops like Grolsch to bottle my beer?
I've heard varying reports about skunking my beer with the green glass, or that the seal is imperfect.  Do you think it would be any harder to clean the glass inside these reusable bottles?  I would consider capping my own beer although I'd rather save the expense until I learn a little more about brewing.
Answer: I have used swing tops in the past without issue. If you are worried about the seal you can buy replacement seals, which should probably be done every once in a while. I don't think it's necessary every time. I have bottled 2 batches using some Fischer bottles and had zero problems with the seal.
As far as the green bottles go. If you keep it out of the light you should have no problems. Beer Advocate has a good explanation as to why the green bottles will not be a problem.
Skunked beer: https://www.beeradvocate.com/archived-articles/527/
Fischer bottle: http://www.enveloop.com/wp-content/uploads/2008/09/fischer-beer-660-ml.jpg
Comment: Good to know about buying replacement seals, and thanks for the green bottle advice.  It's good to know that the swing tops have worked in practice for others!
Answer: I use old Grolsch bottles all the time, with no problems. I keep them in a box (out of the light) when priming, then they go into the fridge when ready, or the basement.
I get many re-uses out of the rubber gaskets, but do inspect them for cracks/tears that may prevent a proper seal.
Answer: I've bottled some of my beer in swing top bottles. I like them pretty well but they are difficult to scavenge (rare) and expensive to purchase. So if cost is your motivator buying a capper (check craigslist) and caps, and fishing bottles out of a local pub's dumpster (ask permission and wear gloves!) will probably be cheaper.
I had one seal fail on me, so you definitely want to get new seals from time to time. The beer in the failed seal bottle didn't skunk, it just simply didn't carbonate. I drank it anyway and it was fine, just flat.
Comment: Worst case scenario = flat?  Sounds acceptable to me.  Unfortunately fishing bottles out of the dumpster isn't the easiest option for me: without a car in Brooklyn, it would be hard to bring new bottles back.  Fortunately, my first batch is in a tiny 2 gallon jug, so I won't need to buy too many swing tops.
Answer: I have a few cases of the swing top bottles in a 1 ltr size. I have been using them for years now without any issues. Every batch I make we use 1 of these bottles to store for at least a year and have had no problems when finally cracking one open.

Is it safe to use swing-tops?


What is the broader acceptance of resignation?

Question: Games that have developed a strong professional circuit generally consider resignation a courteous behavior. Some consider not resigning discourteous. This question is about the rest of board gaming: When (if ever) is resigning acceptable?
Answer: I would say that resignation is perfectly acceptable as long as
1) It was preceded by a good-faith effort to play optimally.
2) All parties who are affected by the resignation agree on its timeliness.
The only times I feel a resignation is discourteous is when it negatively impacts people who were depending on your continued presence;  for example, if Japan were to unilaterally resign from a game of Axis & Allies despite the objection of Germany.
Comment: I agree, and I *prefer* resignation over other things people do, like playing suboptimally (or ridiculously) on purpose.  For example, purposely ending a multiplayer game of Dominion that you're losing (even though it doesn't help you) because you're bored is much ruder than resigning gracefully (which is usually possibly in Dominion will little effect on the remaining players).
Comment: Great answer; I wish I could pick two. I chose the other because it mentioned a few more cases.
Comment: You can always upvote all that have good advice.
Answer: Many people I've played with have a "See it through to the bitter end" mentality. Especially for some of the longer games, like Advanced Civilization, Pax Britannica, and Supremacy. Then again, in those, the game is multi-player, and one player dropping out will drastically alter the flow of play; further, all three have victory conditions that can change the apparent leader to a loser in even the last turn.
I see nothing wrong with offering a resignation, but I also often see it as discourteous to simply walk away.
My usual experience with resignations in long games is one of two situations:

Player has to leave for work. Generally, if this was known before hand, no big deal.
Player is frustrated, losing, and a jerk; player scatters pieces and/or flips board.

On the other hand, while no one I've played with saw offering to resign as inherently discourteous, neither was it discourteous to ask the attempting to resign player to play it out in multi-player games.
Comment: I offer a resignation, and on occasion, my opponent will state a preference to continue playing, at which point I'll continue to play my best.
Comment: Might also be worth noting that some long games (Civ and Advanced Civ in particular) have specific rules for "short games", and playing a short game could significantly alter a player's strategy. Accordingly, I'd consider it courteous that, if the group knows they don't have sufficient time really for a full game, they should all agree *ahead of time* on how long they're going to try to play (even if that goal gets further scotched by misjudging the time). It ticks me to call a Civ game early when people "have to leave" and then have it suggested to just count scores to determine a winner.
Answer: It depends on the type of game:

In a game between two players, I would encourage resigning.
In a game between more players, it depends on the game:

If the game has rules for resigning, or players can agree on a set of rules, resigning should be allowed.
However, if resigning would spoil the game for any of the other players, all players should be encouraged to play out the entire game.

Option 1 is easy: when you're playing chess, there is more honor (and a sign that you atleast understand the game of your opponent) in seeing when you are lost, then in playing on and hoping the other person will make a mistake. When I see I'm lost and I'm sure the other person knows he's won, I will usually resign. Unless when I want to learn from the other player, in which case I'll say "I know you've won, but I want to strengthen my endgame for a bit by watching how you do it" or something like that.
Option 2: for example in Monopoly, a resigning player could just donate his property to the bank, if the other players agree.
But there might be cases where the other players don't agree, for instance when the quitting player will probably be hitting one player's hotels the next turn - the other player may feel his odds of winning decrease when the player goes.
One small tip: if you do insist the game is played to the bitter end, take away the bitter. Grab something to drink and/or to munch on, make jokes, have a conversation. Thank the player for continuing to play, apologize that he still has to play but explain that this allows the other players to end the game as it is supposed to be played.
Answer: One thing to keep in mind is resigning isn't a means to avoid losing, but a recognition that you have lost - you just haven't finished going through the motions.
In a two-player game, this should be fairly simple - you resign, opponent wins, you start another game.
In a team scenario (like Axis & Allies), the entire team should resign as a group - if a single player just packs up and leaves, the other team members should be allowed to fill in the blank spot. (Assuming they wish to continue the game).
In a multiplayer scenario, it really depends on how the interactivity works. Dominion can easily manage a disappearing player, but Settlers can't. Generally, I'd err on the side of allowing someone to bow out, especially if he knows he can't win, but the ultimate winner is still unknown. If it's fairly obvious that someone is going to win (or if it really doesn't matter who wins), I'd rather sweep and reset than force someone to suffer through the remainder of the game.
Answer: That's funny, I was going to use A&A as a perfect example of a game where I would consider it very rude not to resign, although I was thinking about the Axis or Allied players retiring together as a group--I agree that one member of an alliance resigning unilaterally would be in very bad taste.
The criterion I use is that a player should resign when it's obvious that the victor is obvious but that achieving the stated victory conditions will take a long time. A&A is the quintessential example because of how hard it is to captured the "island" of Japan, Great Britian, and North America.
Comment: In this context, A&A is a poor example, in part because it's a 2 team game, and in part because A&A has 2 different victory conditions... Economic, and capture the capitals. Having LOST my capital, playing japan, the German player and we still hit an economic victory when he took Moscow, and I rolled up on india. It's just two varied for a good example for this.
Comment: I don't follow your logic at all. The question is about courtesy in resignation. I've played more than a few games where it was obviously over. As an egregious example, as the allies I had Japan down to nothing but the capital and some of the random South Pacific islands. It was OVER. Yet the other person demanded we play out the four or five more turns required for me to build factories, then ships, then to pound away at the huge stack of INF. Very rude; we never played again. Not giving up if you lost a capital but could still win economically isn't rude: that makes perfect sense.
Comment: A&A has so much luck factor, that even an optimal position can be lost in a couple turns, multiple routes to victory, shared victory, and no true player elimination (if your allies retake your homeland, you get it back). I've seen a player who had a 20infantry:1armor advantage lose a battle on several occasions... simply by luck of the dice. And further, a player dropping out means more work for some other player, since the 5 core nations are all played regardless of how many players. It is the perfect example of a game where resignation is a rudeness.
Comment: Obviously one player can't drop out. It would be one entire side resigning. And yes luck can play a large role in games, but if that's a risk then the resignation is occurring too early. The allies don't have economic victory so they could have every territory on the board except Japan and the game wouldn't technically be over. There is no chance of dice saving that situation or one even remotely close to it. If all three of the allies are left, Germany is eliminated, and Japan is being steadily pushed back: it's over. Given 84 IPC victory for the Axis, the Allies probably should never quit.
Comment: Another thought that occurred to me last night: in a game where extreme luck can turn the tide but where both players think the game is out of hand, resigning is probably the most sportsmanlike thing to do. What are the possible outcomes. The game plays out as expected: hours spent rolling to find out the player who was dominating won. Something really strange happens: and the player who deserved to lose uses dice to snatch victory from the jaws of defeat. That's a hollow win in my book only a poor sport would be proud to have. Better to resign and admit you were outplayed.
Comment: Being upset over losing in a high luck game is the epitome of bad sportmanship.
Answer: In a two player game, the time to resign is when it is certain (or almost certain) that the weaker party will lose, given the playing abilities of both parties. That could be a disparity of as little as two pawns in chess (at the master level), or a piece, major or minor, for weaker players.
There are some multiplayer games like Diplomacy, where a single player can "declare civil disorder" without substantially affecting the chances of other players. On the other hand, if you are part of a pre-set "team" (Axis and Allies), it's better to resign, if at all, as a team.
Answer: In board games played online that have score values resigning may be considered rude.
For example, if you forfeit in Scrabble Online, you prevent your opponent from scoring, thus ending their opportunity for a high score value (which is tracked and viewable by opponents).
Comment: I don't think that's an issue with resignation as much as with expected behavior in an environment where statistics other than wins and losses are tracked. (This may be much more of a factor in online games - and thus more of a gaming.SE response - but I'll look at only that which could be applicable to board games too.) There are, or should be, distinctions between being in a Scrabble league, where there is most likely a code of behavior governing play, and simply playing random opponents. Is a lost high-score opportunity any worse than a high score gained when the opponent stopped trying?


Do permissive or copyleft licenses have a limited term based on US copyright law?

Question: If you write a book, the copyright for that work is protected for a long time, but the work will eventually enter the public domain under US copyright law. Does the same thing apply to pieces of software released under a permissive open source license? Would software released under a BSD, GPL, or MIT license automatically enter the public domain at some point in the future? I know that copyright law changes frequently and retroactively, I'm just curious about how the current laws would apply.
Answer: Theoretically, the license itself is not time-limited - once the code has been released under any of the MIT, BSD, GPL or Apache licenses, it is available under that license in perpetuity. If 200 years from now you wanted to distribute the source to version 5.0 of the Linux kernel via the GPL, you could.
However, when the copyright expires (70 years after the death of the author or whatever), everybody gets the ability to distribute the code however they like so they would no longer be required to follow the GPL, any other open source license, or for that matter any proprietary license. Open source licenses rely on copyright law for their effectiveness just as much as proprietary licenses do, and they all cease to be effective when the copyright protection expires.
Comment: Something happened with my edit. Only CC0 (maybe "unlicense" too) isn't proprietary license, all the others are. Also, you can contrast open source with closed source but not with proprietary, since they are both proprietary.
Comment: @Smart455 That's not what proprietary means.


Do you have to do the [EXTREME] missions?

Question: In Metal Gear Solid 5: The Phantom Pain, is there a way to avoid or not do the [EXTREME] missions? I did all of those up until Metallic Archaea.
Answer: They are completely optional unless you want 100%, I got the true ending without doing any of them. You only need to do the missions and side ops that are marked in yellow. When you run out of those, just 'pass time' by doing any side ops or replaying old missions for a while, and eventually you'll get calls progressing the story and unlocking more yellow missions. You'll have to do that a couple of times.
Answer: You need to do the extreme missions, however, I found out that there are ways you can do them without being an active participant. Like in mission 31 where we have to take Sahelanthropous, i hid behind cover in a valley where he couldn't see me at all and order bombardments and air support from my i-droid. I hope i was of some help without spoiling it for you. This is the best part of the game that it stays true to the idea that you can choose anyway to approach the mission.
Comment: Frankly i found riding D-Horse best, it let me empty my explosives into it while staying highly mobile. Seriously though this isn't relevant to the question that mission is neither Extreme nor optional
Answer: I finished all yellow side ops and yellow missions because I suck at stealth and didn't want to attempt them with no reflex mode.
But after you do yellow missions and side ops, just pass time with more side ops and some fob and eventually you'll get a call progressing the story.
Comment: There was an answer already, but I appreciate the thought.


Which Lego Police set or sets do I have?

Question: We were given a big bag of Lego pieces.  When sorting through them my son found a bunch of police pieces but we can't figure out which set or sets they belong to.  I've tried looking up a few individual pieces but that hasn't helped and I can't seem to find the right set or sets by looking at googled images.  Any help would be greatly appreciated.
Answer: Most of the parts are of set 7288.
I see at least the following:

Window / door with the gates
Big wall parts with stickers.
Cop minifig & white shirt criminal
Computerdesk and front of the truck
Red front of the small car

I also see parts of 7279:

Gray shirted criminal
Part of the ATM terminal
Parts of the little car (lights and front with sticker)
Maybe the dog, it's hard to see the print of the head on the photo.

Then remains the stick of dynamite, the minifig in front of the red car parts, the second dog and bigger white bricks, that are not of these 2 police sets.
Maybe you can take a look for yourself on Brickset.com. The remaining set(s) are probably from around 2011, as these 2 are. Maybe look for a kind of plane / helicopter, because of the slope pieces.
Answer: At least  the mobile police post 7288; the label  on the piece identifies it.
Look for pieced used as license plates; license plates on Lego cars often contain the set number.  In fact, any number printed or stickered on a piece is likely to be the set number.
The dog doesn't have to be from a police set; he also appears in at least one firefighter set.
Answer: The white two-legged assembly with the blue light that's just above the left dog looks to be part of the robot dog from Space Police set 8399.
Additionally, the minifig near the red car front appears to be from the World Racers theme and the one just under it that's missing its head looks like Johnny Thunder from the Adventurers theme.


Are there any websites that sell DRM-free Japanese e-books?

Question: I'm familiar with the Japanese e-book stores Kobo, honto.jp, and Kindle, but all of their books seem to have DRM, and none of them allow you to read books on your computer. Are there any bookstores that sell DRM-free e-books in Japanese?
Answer: You can find gratis, DRM-free versions of older books whose copyright has lapsed at 青空文庫 (additional formats available at Internet Archive).
Answer: You can remove the DRM from Kindle books and convert to most major formats without too much trouble using Calibre or other software. I am not a lawyer, but in the US at least, you have the right to do so (cf. decrypting DVDs).
Comment: Thanks! The problem I'm running into is that all the Japanese-language kindle books I've looked at cannot be downloaded to the desktop versions of the Kindle app, and so I cannot get at the AZW file in order to convert it. I've also tried accessing the version downloaded to the iPhone Kindle app, but it seems to be storing it in a different format. If you have any ideas, please let me know!
Comment: Anything related to your country location settings? I remember having trouble getting access to books I ordered depending on the language/region detected on different devices.
Comment: I don't think it has to do with my location, although for what it's worth I live in Japan. The page on Amazon states "Available only on these devices", and doesn't list Kindle for Mac or Windows. The "Deliver To" drop-down has Kindle for Mac grayed out. It's the same on both amazon.com and amazon.co.jp. Here's one example: http://www.amazon.com/Give-Regards-Black-Jack-Japanese-ebook/dp/B00BN0R1OO/ref=sr_1_4?s=digital-text&ie=UTF8&qid=1389686039&sr=1-4
Comment: This looks promising: http://www.epubor.com/prc-drm-removal-for-kindle-android-books.html Is the format on mobile PRC, not AZW? Also, nice recommendation!
Comment: Nope, it doesn't appear to be PRC either. It's a [folder](https://dl.dropboxusercontent.com/u/6706381/kindle-book-iphone.tiff) with three files, book.kcr, book.kcr-shm, book.kcr-wal, and a folder resources with a bunch of binary files in it. It looks like book.kcr is actually a core data database, so I'm pretty sure this is all some sort of pre-processed version specifically for iOS. =/
Comment: Sorry, I don't have any iOS devices at the moment, but I'll take one more shot: http://apprenticealf.wordpress.com/2011/01/13/ebooks-formats-drm-and-you-%E2%80%94-a-guide-for-the-perplexed/
Comment: Hmm, at first glance I don't see anything resembling those formats. I'll do some more investigating. Thanks for your help!
Comment: Did you ever get anywhere with this? I'm having exactly the same issue


Really lost FaceBook password

Question: Help, please, a friend, and client of mine cannot afford to lose her FB account. The password she created does not work, she has no "Trusted Contacts" to use to regain access and repeated attempts to reset the password through FB do not generate a reply, neither text nor email. We suspect a hack, but there are no posts to make it obvious. I have tried resetting the password it for her myself and we never get a reply from FB. She still has access to FB from her phone, but if she ever loses that phone or when she upgrades, she will have no recourse. Are there social media marketers for hire with actual live connections to humans at FB? I have followed every action possible, including looking at stored passwords on her IPhone settings. Nada. How she still has access from her phone I cannot understand, but I guess the FB app has it encrypted somewhere. Apparently, nowhere we can see.
Answer: Does she still have access to the email ID associated with this Facebook account?
If yes:

Click on forgot password and follow the link/instructions you receive on that email
If you're logged in but have forgotten your password, follow the steps under Change Your Password then click Forgot your password? and follow the steps to reset it. Keep in mind that you'll need access to the email associated with your account. (Taken from https://www.facebook.com/help/213395615347144) - This one will work since you say she is logged in on her phone.

If she does not have access to the email ID then you can try changing the email ID associated with the account from the app where she is logged in.
Comment: Thank you- she does, but the email never arrives. I have tried both procedures you describe. In order to make changes the app asks for a password - not for posts, but for security changes.
Comment: Did you check the spam and promotion folders in her mail box?
And what email address does it show inside the account section in the Facebook app?

Also is her phone number connected to her Facebook account?
Answer: OK, it turns out FB was just blowing us off. (fix below message from FB) This was their one and only response after several attempts over several weeks (before and after sept 21) . Of course we found this today in a spam folder.
From: Facebook email@example.com
Sent: Monday, September 21, 2020 11:02 AM
To: Gl Nm <@.com>
Subject: We can't review your ID right now
Hi S******,
We have fewer people available to review IDs due to the coronavirus (COVID-19) outbreak.
We're only able to review IDs for the most urgent cases. This means we can't review your ID right now. Please try again at a later date. Thank you for understanding.
The Facebook Team

The way we fixed this was as follows: FB was still logged in, in her phone. Although we could not add an email address without being prompted for a password, nor change her phone number, we were able to add a second phone number without being asked for one. Why?- no clue. Once we added her husbands number, we used it successfully as a recovery number to receive a code. Why her own cellphone could not receive a recovery codes from FB? No clue. How you get on FaceBooks "Urgent List"? No clue. So many questions unanswered. Still, we are back in business, which is what matters the most. Thank you Harsh for your help. Truly appreciated.

Really lost FaceBook password


How can I determine which direction I'm facing?

Question: In Minecraft, it's useful to know which way is north in order to determine how to manipulate mine cart tracks. Usually, people keep track of which way is north by placing torches on the northern walls of their mine shafts. How can you initially determine which direction you are facing? (Above ground)
Answer: Using cobblestone, there is an "L" shape in the block looking at it from the top. When the "L" is in the top left corner and right side up, then you are facing north.
Please refer to this awesome paint diagram.

Note: Once seen, can not be unseen.
Also works on netherrack.
Comment: 1.8 update: Jeb has announced a new texture for cobblestone, which means the 'L' method will no longer work. No change has been announced for the netherrack texture, though, so this method may still work with netherrack.
Comment: +1, due to the availability of cobblestone, this is a much better answer than most of the others. It's what I use.
Comment: I think this is the best method of determining north. It works when you can't see the sun, only requires common materials, and works even in the nether.
Comment: The new cobblestone texture has appeared in 1.7, and it still has an 'L', although the 'L' is now in the top right of the block.
Answer: In addition to what sjohnston said, clouds always move west.
Comment: This to me is the easiest way.
Comment: [Clouds move towards **west**](http://www.minecraftwiki.net/wiki/Clouds) since a long time ago.
Comment: @AlvinWong Thanks! I haven't played Minecraft in quite a while, so I didn't realize this changed. I've updated my answer.
Answer: Above ground, you can use the sun or moon to orient yourself.  They both rise in the east and set in the west. Also, according to an answer here, you can punch the ground, and the pattern of cracks will always be oriented the same way relative to north.
Finally, there are third-party mapper programs that you can use to orient yourself (although I haven't used any and can't vouch for them). Some players might consider this cheating, or at least unsporting.
Comment: Whoops didn't notice the question you linked; I think my question might be a duplicate.
Comment: @Kevin, it's not :)
Comment: In versions prior to beta 1.9.4 (and the XBox version), the Sun rises at the "top of the map". So either you are holding the map with North on the left (unconventional), or the Sun actually rises in the North and sets in the South! http://www.minecraftwiki.net/wiki/Day-Night_Cycle
Answer: A great trick is to use redstone ore. When you place down the redstone, there is a cross shape on the block. On two of the 4 arms, there are rectangle shapes. When you orient yourself so that one of the rectangles is to the left and one is in the front, you're facing north.
Comment: I'll insert it for you.
Comment: Brant user posted this in the chat: http://chat.stackexchange.com/transcript/message/143539#143539 It shows how you can use the Cobblestone and Hellstone texture to orient yourself. But be careful! What is seen can't be unseen!
Comment: This no longer works, as the redstone texture has been changed.
Comment: Can you give us a picture of what this looks like?
Comment: minecraftwiki.net/wiki/Redstone_(wire) should work. I can't put up a picture right now as i am operating under a firewall that blocks Mineapedia; i can't download the image. Sorry.
Comment: I love this method for when I am underground!
Comment: A better trick is to press F3 and look if it says North, South, East, or West
Comment: I think the texture was rotated 90 degrees. So what was N in the picture is now W
Answer: Press F3 to get the debug menu, then look under the x, y, z coordinates and see the letter "f". This gives you the direction you're facing (0 south, 1 west, 2 north, 3 east).
If you need more help then you can also go to the Minecraft wiki and look up anything you may need.
Comment: This should be the perfect modern answer
Comment: +1, I'm baffled that this isn't listed higher. Having the answer printed in text form in front of your eyes definitely beats looking for odd details of textures, which might not even be relevant if using a resourcepack, which is very common nowadays. This also works underground and in any dimension.
Answer: The current answers are excellent.  You could also try Zan's Minimap Mod, which works in both SSP and SMP.  However, since Minecraft 1.6 is releasing this week, and one of the new features is going to be a map, this mod may become obsolete very soon.
You can also set waypoints with it.

EDIT:
Since the maps of Minecraft 1.6 are virtually useless, I've just installed the new update for this mod, which now displays coloured wool as the appropriate colour, and as a bonus, no longer requires Modloader to install.  I'll also include a video of the mod in action.
Comment: Handheld maps, mind. If people aren't able to read the maps (and thus orient themselves) mods like this will still be better, and will probably remain simpler to use to boot.
Answer: There is a program called cartographer, and if you build an arrow on the ground and then load your map in cartographer, you can see what direction your arrow is pointing...
But if you know the direction of the sun moon and clouds, you can then orient yourself from there.
Consider building landmarks to keep yourself oriented quickly
Answer: This is an old question, but now you can easily see the direction you're facing in the F3 stats:

Look for the field that says "Facing", on the left. It will be north, south, east, or west.
Comment: Thank goodness. I was looking at all these weird, time consuming answers about small texture details.  I was beginning to think nobody else knew about just hitting F3
Comment: @MacedonZero there's one other answer that mentions F3, but it must be for an older version. Nobody's probably been on this question since they added this to F3.
Answer: If you have a few minecart tracks available, you can use the south-west rule to orient yourself. There are two ways:
Orienting yourself using cross-intersections (and a minecart)
You need one minecart and at least 5 track pieces.
Lay out two cross-intersections (or lay out one, destroy, and lay out the second). Then, put a minecart on it, push the minecart and watch the direction it moves when hitting the cross.
Look at this image from Minecraft wiki to understand what I mean.
Orienting yourself using T-intersections
You need 4 track pieces.
The T-intersections also try to follow the south-west rule when they are laid out on the ground. If they are unpowered (no button or redstone powering the T), the curve will try to point to south-west. So, if you lay out two T-intersections, you can orient yourself.
Look at this image from Minecraft wiki to understand what I mean.
Answer: You can find East by keeping a sunflower handy. When placed, sunflowers always face east.
Answer: A map can easily and precisely tell you which direction you're facing.
Craft a map, put paper around it until it's the largest size, and you can easily determine your direction at any time in a large area.
Answer: Cardinal directions: (West is the direction of the clouds and sun, going to the left when facing North.)
North = -Z, South = +Z, West = -X, East = +X


How to obtain standard surveys / measures to use at end of experiment to "control for altruism" etc?

Question: When running an economics experiment, how and where are experimental graduate students supposed to obtain the surveys (such as standard measures of altruism, risk aversion, social dominance...) that often come at the end of experiments (so that researchers can "control for altruism" etc)? Do researchers purchase such measures / inventories, or are they part of the public domain and can be freely copied from previous research papers that use them? I am interested in using those from my own field as well as using one that is not from my own field (the Bem Sex Role Inventory) that appears to not be readily available online -- at least not for free.
Answer: In experimental economics, the classic ways to measure/control for participants' social preferences are variants of the following games:

The ultimatum game measures a participant's preference for fairness or justice.
The dictator game measures a participant's other-regarding preference.
The trust game measures the level of trust and trustworthiness among a group of participants.

Risk preferences (and time preferences/impatience) can be elicited using either of the following:

Multiple price lists (see Holt & Laury (2001))
BRET (Bomb Risk Elicitation Task)
Convex Time Budget (CTB) method (for time preference, see Andreoni & Sprenger (2012))

The games other than CTB are simple enough to be ran in the "survey" form, e.g. with pencil/paper. There are also free computer programs (e.g. zTree) that implement those games.
NB. If your main audience is economists, you'd also want to run these games in an incentivzed way, namely participants get paid and their earnings are directly related to their choices in those games. Responses to survey questions, especially the hypothetical type, do not get much credit from economists.


Why can't wizards create precious metals?

Question: I've been curious what stops wizards from creating and endless supply of wizard currency. After looking at a few other questions (like this, and this) it keeps getting stated that wizards can't create the precious metals needed to create more of the wizard currency. However it doesn't appear to be explained why they can't create those precious metals. I was hoping someone could explain why, what about magic limits it's use so it can't be used to create precious metals?
Comment: Something to do with Gamps law?
Comment: I would agree with Carl that there is a restriction in simply creating the currency out of thin air. However, you may have better luck rephrasing your question to ask whether or not wizards of the Potterverse practice alchemy of this sort.
Comment: Didn't Ron in the movies give muggles conjured gold as cash?
Comment: Ever heard of "fairy gold?" It looks real, but mysteriously dissolves soon after use.  There are tons of implied alchemical references in the Harry Potter novels, but it is not emphasized as a plot device.
Answer: In addition to Slytherincess' excellent answer, you have to remember that in UK wizarding world, the bank(s) and currency is controlled by goblins. This leads me to believe that goblins are also responsible for the creation of currency.
Now yes, theoretically, someone could make another Philosopher's Stone, which they then use to turn some basic metal into gold, then magically melt it down and shape/design it to appear as a real Galleon. However, goblins (who again control and likely forge the currency) are able to distinguish the subtle differences between goblin made metal items and wizard made replicas of said items (i.e. the Sword of Gryffindor in the Deathly Hollows). This would hold true for any wizarding counterfeit currencies.
Now think of this from a governmental perspective (a little off topic, but there it is). I don't know about other countries, but in the US, there is, and always has been a problem with dishonest people attempting (and in many cases succeeding) in counterfeiting currency. By allowing goblins, the one race that can forge metals in ways humans (wizards included) are unable to, and can distinguish the difference between goblin made currency and wizard made currency, you effectively control how much counterfeiting can be done, as the counterfeit currency would never make it past the bank!
Is this likely to prevent someone like Mundungus from creating a counterfeit galleon and passing it off at a shop in Diagon Ally? Probably not, but I am sure the wizarding world is probably advanced enough to be able to trace a counterfeit (once identified at Gringotts) back to the creator.
Answer: Well, wizard Nicholas Flamel, owner of the Philosopher's Stone, could have had the capability to make gold using the stone, gold being a precious metal.
As far as I'm aware, nowhere in canon does it say that wizards cannot make precious metals (And the existence of the Philosopher's Stone in the Harry Potter universe would suggest otherwise.). Actually, nowhere, I believe, does it say that money cannot be made magically -- meaning, it doesn't state this outright. However, my canon-based guess is that the creation of precious metals for the sole purpose of creating currency would perhaps violate Gamp's Five Laws of Elemental Transfiguration.
I think it's important to remember that metals considered precious by humans may not be considered as valuable by wizards -- perhaps metals other than gold, silver, or bronze might have more magical properties, and therefore be more valuable in the wizarding world. Just an idea.
Answer: Perhaps it is like bitcoin, where anyone can make it, but making new depends on how much there is already in existence, and it gets harder the more exists.
Answer: I think of Magic as not being able to "create" but it can "summon" or "transform." For instance, any magically-produced food is either transported from a remote kitchen, or derived from available energy + matter.  In the case of gold, since no one knows the "recipe," the only way to conjure up real gold is to transport it from another location. If you owned it, then it is legit. If not, they you just stole it.


How can I color a mixed object in Illustrator?

Question: I have a mixed object (a group of either stroked or filled paths) in black and white, and I want all of the blacks to be blue.  I know I can go into the group and select each black path and change it to blue, but there are a lot of paths, and I'm wondering if there is a quicker way to do it.  In Photoshop, I could just create a coloured layer and change the blending mode, but this doesn't seem to work in Illustrator.
Answer: In your main menu, you got a menu item called "Selection". Just take the "similar" sub menu item - you need have one of the items selected - and choose which type of similarity the elements you want to select should share. You then have a complete selection of all element that are equal in one or another point.

I don't have an english version, so you should simply count the elements to find the menu item.
Comment: This works great.  However, you need to ungroup any mixed objects.  All in all, the best solution.  Thanks!
Comment: @bozdoz You don't even have to ungroup them. You can just double click the group to isolate it and then select stuff inside the group. This works unless you need to cross select stuff in groups. But maybe even this works if you use the direct select tool - key: [A].
Comment: Not sure.  With my file, I had to ungroup. *shrug*
Answer: Two ways of doing this,
one,
put all the "blacks" in one group, then use the group selection tool and click on the one of the "blacks", you can then change the color to "blue"
second,
Use the magic wand tool and let the fill color box be checked, click on one of your "blacks" magic wand will select all objects with black fill.
To select objects with black stroke you can click on the flyout menu inside the magic wand panel and add more selection criterion like stroke color and stroke weight.
Once selected you should be able to change the blacks to blues.
Comment: I suppose this is a quicker way to do it; I was wondering if there was an automatic way of doing it.  Thanks. :)
Answer: I found out how to do it in an easier way.  You can create a colour group, click on the group, click "recolor artwork", select a single color, and select the colour group with the colour in it.  Worked well.


Does WSUS update anti-virus programs?

Question: What is WSUS (Microsoft Windows Server Update Services)? What settings do I need at client sites to use WSUS? Does WSUS update anti-virus products, or does it only support Microsoft Software updates?
Thanking you,
Sadiq
Answer: WSUS supports updates for Forefront antivirus from Microsoft for antivirus updates. As far as I know it does not support the downloading of 3rd party AV updates.
You obviously need WSUS setup on one of your servers. If you use Active Directory you can use Group Policies to apply the settings to your workstations.
If you do not have AD then you will have to make some registry changes. The best way to go about this is to make the changes on one machine, test it and then export the registry settings and import it on the other computers.
The instructions for GPO and the registry are here.
Answer: System Centre Updates Publisher (SCUP) is part of System Centre Config Manager (the latest version of what used to be called SMS). SCUP is Microsoft's upgraded Enterprise version of WSUS that uses the WSUS engine but is able to push out updates to 3rd party software as well as normal Microsoft updates.
A number of 3rd parties supply update catalogues that you can subscribe to in SCUP in addition to Microsoft's WSUS update catalog. These include Adobe (for Flash player, requires agreeing to their distribution agreement, here), HP, Dell, Sun and Citrix. An (outdated) list of catalogs is available here http://www.microsoft.com/smserver/partners/itcucat.mspx more can be found by querying suppliers web sites.
Unfortunately I'm not aware of any anti-virus companies that make their updates available in a SCUP compatible catalog. Most of them use their own proprietary server products to distribute updates within a company LAN.
Answer: WSUS is basically Microsoft updates but it pulls it inside your network and gives you control over what updates a computer gets.  This can be beneficial if there are updates you DON'T want computers to get, or if you want to spread out how an update due to the size (Like Service packs which are very big and can choke your network if you don't space out the computers downloading it.)
It is also able to report to you what computers have what updates and lets you know when computers have issues with installing updates.  This gives you pretty good control over the risks of unpatched systems.
Answer: For WSUS you will need a Windows server, I believe 2003 onwards. You can download the WSUS server software from Microsoft, as well as implementation documentation. Client machines can be configured through policies, either local or group, to connect to a specific server for their updates, as well as the other WU settings.
In regards to the antivirus updates - No, unless it's Microsoft's offering. When WSUS was released Microsoft told us that by version 2 it would be able to support 3rd party software that used the correct API. Neither the API nor support for 3rd party software has yet to be seen.

Does WSUS update anti-virus programs?


Is there an upper limit to the maximum cumulative reward in a deep reinforcement learning problem?

Question: Is there an upper limit to the maximum cumulative reward in a deep reinforcement learning problem?
For example, you want to train a DQN agent in an environment, and you want to know what the highest possible value you can get from the cumulative reward is, so you can compare this with your agents performance.
Answer: In any reinforcement learning problem, not just Deep RL, then there is an upper bound for the cumulative reward, provided that the problem is episodic and not continuing.
If the problem is episodic and the rewards are designed such that the problem has a natural ending, i.e. the episode will end regardless of how well the agent does in the environment, then then you could work it out by calculating the max possible reward in each step of the episode; however this is potentially non-trivial depending on your environment.
For an example in a trivial setting, however, imagine the problem of cartpole -- I could define the MDP to have a reward of +1 for every time step that the agent is able to balance the pole upright, and 0 when the pole falls. If I also defined that the problem terminates after 200 time steps then the upper bound on cumulative rewards for this problem would be 200.
In general, if the problem is continuing then in theory the problem goes on infinitely and so there is no upper bound, as the episode never ends -- this is partly why we use the discount factor, to ensure that $\sum_{k=0} \gamma^k R_{t+k}$ converges.
Comment: "In any deep reinforcement learning problem, not just Deep RL", you mean in any reinforcement learning problem without deep right ? Also, just because problem is episodic doesn't guarantee that sum is finite. You could set up your rewards such that agent never wants to end episode even though there is a terminal state which would make environment episodic. You would need to add discount factor to guarantee boundness.
Answer: My answer to:Is there an upper limit to the maximum cumulative reward in a deep reinforcement learning problem?
Yes but depending on the environment, if dealing with the theoretical environment, where there are infinite number of time steps.
Calculating the upper bound
In reinforcement learning (deep RL inclusive), we want to maximize the discounted cumulative reward i.e. Find the upper bound of:  $\sum_{k=0}^\infty \gamma^kR_{t+k+1}, where$ $\gamma$ $\epsilon$ $[0, 1)$
Before we find the upper bound of the series above, we need to find out if the upper bound exists i.e. whether it converges according to the environment specifications such as the reward function.
I will provide one example environment where the series converges. It is an environment that has simple rules and goes on for infinite time steps. It's reward function definition is as follows:
-> A reward of +2 for every favorable action.

-> A reward of 0 for every unfavorable action.

So, our path through the MDP that gives us the upper bound is where we only get 2's.
Let's say $\gamma$ is a constant, example $\gamma = 0.5$, note that $\gamma$ $\epsilon$ $[0, 1)$
Now, we have a geometric series which converges:
$\sum_{k=0}^\infty \gamma^kR_{t+k+1}$ = $\sum_{k=1}^\infty (1)(2\gamma^{k-1})$ = $\sum_{k=1}^\infty 2\gamma^{k-1}$ = $\frac{2}{1 - 0.5}$ = $4$
Thus the upper bound is 4.
For environments that go on for a finite number of time steps the the upper bound does exist but for certain environments, likewise for the infinite time step environments, it may be a bit difficult to calculate but not necessarily impossible, the environments I speak of are ones with complicated reward functions and environments i.e. the environments are stochastic or the reward function's possible values are dependent on the state, they always are but we can loosely say that a reward function is independent of state when all possible reward values for an environment can be given in any state, obviously with regards to the actions taken though.
Answer: Lets assume $\sup_{s,a} r(s,a)<b$. Then for continuing problems the upper bound can be obtained by
\begin{align}
\sum_{t=0}^{\infty} \gamma^{t}r(s_t,a_t)
&\le \sum_{t=0}^{\infty} \gamma^{t} \sup_{s,a}r(s,a) \nonumber \\
&=\sum_{t=0}^{\infty} \gamma^{t} b = \frac{b}{1-\gamma}.
\end{align}
We can use the same bound for episodic tasks with discounted return.
For episodic tasks without discounting ($\gamma=1$) the above sum goes to infinity. However, if we know the episode length $T$, we can use $Tb$ as an upper bound.
Comment: The last part, where you say Tb can be used as an upper bound, may not work since e.g. The reward is 2 for every favorable action during the episode and 100 is given for the action that takes your agent to the goal state is an edge case. Technically Tb will be an upper bound but won't be sufficiently accurate for use. I think the solution for continuing problems is good.
Comment: I agree. There might exist tighter upper bounds, but they require further information about the problem. $Tb$ can be used for any problem.


Wamp Is not working after reboot

Question: I'm running win 7 x64, I just install a custopack theme among a few other things, rebooted and now when I run wamp, the icon stays orange
Port 80 is not used by anything. At least, skype has been set to use another plus it's not even running and wamp says port 80 is ok.
Other than that, I recently fiddled with vhosts and a few other things a few days ago. But the problem appeared right now after a reboot.
Thanks in advance.
Comment: Don't thank us, thank SuperUser.com
Answer: Fixed: I simple re-installed wamp. Random :S

Wamp Is not working after reboot


How do would you create an "imitation" of a sound you've already created?

Question: I was just listening to bunch of scenes on the website MovieClips, and while watching this Raptor scene from Jurassic Park III I got curious as to how they got that sound whether they actually made the prop so it produces the sound or whether it was designed, any ideas? If you had to do something similar how did/would you approach it?.
Comment: Are you referring to the strange flute?
Comment: @Christian Yup.
Answer: If its flute related, I had a bit of experience when working on The Warriors Way of needing the sound of the last air exiting a neck wound after someone was killed by a Samurai - the script referred to it as a 'sad flute'
I experimented with a lot of ideas but got the best results by hiring a local guy who is a genius with all sorts of wind instruments. He has a massive collection from many different culture but also is very skilled at various playing techniques (overblowing to create harmonics etc)
http://en.wikipedia.org/wiki/Overblowing
Myself and the director got him to try all sorts of musical & non-musical/atonal phrases that I then messed with..  For my use I also filled a few ocarina and bamboo flutes with water and yoghurt, and captured elements to simulate lungs filling with blood etc...
fun!
Comment: @tim hey I just watched that on Netflix the other day!  Congrats, really fun flick!  I don't even think I could count how many neck wounds there were...
Answer: I'm pretty sure it'd just have been sound designed. I don't think there would be time and budget to spend on designing functioning props like that; it would essentially be like designing a musical instrument specifically for use in a couple of scenes!
The design of the sound would probably have involved the use of some flute sounds, the lower parts from blowing across something like a drainpipe.
Answer: Old Disney cartoons used a lot of purpose built machines for sound effects, but that is as far as I know very rare now.
Answer: I can't say for sure what it originally was that made that sound, but it wasn't from the prop. Like Tim mentioned, it might very well be some kind of flute, very possibly a Chinese or Japanese flute played by someone truly brilliant. My guess is the Shakuhachi.
It does sound very bamboo:ey.


Fill prices on limit and market orders

Question: Suppose the book of ticker X is empty. Simultaneously trader A sends a limit buy order for 1 unit of X at price 2$ and trader B sends limit sell order of 1 unit of X for 1$, what will happen? What is going to be the fill price? Same question for market order, suppose the book for ticker X is empty and traders A and B send a buy and sell market orders (without prices) is the fill price going to be the last fill price? how is the fill price determined in such case?
Answer: In the first case it is a "race condition": whichever order is received first (even if it is only one microsecond before the other) will populate the Book and the second limit order will execute against it, at the price of the first order.
In the second case it is indeterminate and may depend on the details of how the "matching engine" works. Probably when the first market order is received against an empty Book, it will be rejected and so will the second since the Book is still empty.
Both of these are "edge conditions" or peculiar cases where the result may be highly implementation dependent.
Comment: I would add that at the CME the depletion of the limit order book during trading hours would be considered highly unusual and probably triggers a market halt, with the market re-opening only if and when the limit order book fills again. In this "pre-market" state arriving market orders are held back in a queue awaiting market re-open.
Comment: Although there is another answer which says differently, your answer makes more sense to me.
Comment: @noob2 the order book is very frequently empty in one side on some underlyings, it does not cause a halt. A market buy order however with no offers i believe will trigger a halt.
Answer: While the behavior is generally exchange-dependent, in the first case, the orders are likely to get crossed at $1.50, and in the second, both return unfilled.

Fill prices on limit and market orders


Can a fighter jet be hit by guns?

Question: Can a fighter jet travelling at fast speed be brought down by a weapon like an M134 Minigun or any machine gun?
Comment: I'm voting to close this question as off-topic because It attracted only answers with a military background. The question is specific to ballistics and weapons, the only connection with aviation is that it is "about" a fighter jet.
Comment: @BogdanWilli - Ehhhh.... AAA is a pretty important fixture of military aviation and has had a big impact on their design and how they're operated. You don't really have to know much about their ballistics to appreciate their effects on operations. If I have time, I'll edit in some more info on how AAA has affected a/c design.
Comment: If the bullet and the aircraft's trajectories are convergent, the bullet will hit the aircraft, whatever their velocities. Put the bullet in the adequate trajectory require some skills (and a good gunsight)
Comment: related: http://aviation.stackexchange.com/q/13600/1467
Comment: @HephaestusAetnaean: What is AAA? can you explain please? Your answer is quite a good answer indeed. But still I think the whole thing (especially your answer) would be better on [skeptics](https://skeptics.stackexchange.com/) or on another military or stragegy related website. See in the [help center](https://aviation.stackexchange.com/help/on-topic) that also Rocket -related questions are off topic.
Comment: @BogdanWilli - Ah. Fair enough. I forgot the scope of Aviation.se; the F-16 and B-52 questions were fresh in my mind. ....... BTW, AAA = antiaircraft artillery (think WWII flak... sort of). It basically forces a/c to fly at higher altitudes so that they can't hide in the ground clutter and between hills/mountains etc. It spurred (in part) the development of better radars, stealth, better air-ground sensors, and modern multirole fighters like the F-35. And it made life very difficult for low-level a/c like the A-10, F-111, and B-1.
Answer: They're called SPAAG's -- Self Propelled Anti-Aircraft Guns. Older systems tended to fire 23 mm shells. Newer systems tend to fire 30 mm shells augmented by short range missiles.
They are equipped with radars and high-speed elevation and traverse motors for the turreted guns, so they can react quickly to fast a/c flying low ahead. They're also useful against attack helicopters, which also hug the ground (see below).
These are short range weapon systems, typically only effective under 10,000 ft, the guns at much less than that.
They're still useful even today. Medium and long-range SAM's have forced a/c to fly low, below their search and fire control radars, but within range of the guns.
This was standard NATO doctrine during the late Cold War---low level penetration---and gave rise to the F-111 (for example), which was designed to fly fast and low, hugging the bumpy terrain of Central Europe. This would have worked very well had the Soviets not fielded SPAAG's (basically modern AAA) and developed their own MANPADS (shoulder-fired SAM's). Soviet AWACS and look-down shoot-down radar also contributed to the decline of this tactic. These systems denied the use of low-level airspace so effectively that during Desert Storm, the Coalition air forces basically gave up low-level operations within the first week and switched to bombing from medium altitude exclusively (above the reach of AAA and MANPADS). Not even the A-10 with its titanium armor could long survive in that environment. Afterward, they did occasionally venture below 10,000 ft, but typically with special permission and enthusiastic support. Even after the first week, when Iraqi air defenses were ineffective, few a/c still flew below 10,000 ft because the AAA and MANPADS were too numerous to be eliminated entirely.
NATO air forces are getting around this problem by buying stealth fighters, namely the F-35A, which can hide from SAM radars, allowing it to fly at medium/high altitudes, far above MANPADS and AAA. But that's for another question/answer.
Here's an older Shilka (Vitaly V. Kuzmin - http://vitalykuzmin.net/?q=node/306):

A later Tunguska (Leonid Dzhepko / Л.П. Джепко):

And a modern Pantsir (Vitaly V. Kuzmin - vitalykuzmin.net):
(All images taken from their respective wikipedia pages.)
Answer: Can a fighter jet traveling at fast speed be brought down by a weapon like an M134 Minigun? or any machine gun?
There are machines guns designed to bring down cruise missiles and jet fighters but they look like this:

see: The Phalanx CIWS close-in weapon system for defense against anti-ship missiles.
Comment: @Hugh - It works fine on both, assuming they're within range. a/c are often easier to hit, often being larger, slower, and less maneuverable. Phalanx can also target surface vessels, rockets, artillery, and mortars. But, yes, the motivating role is missile self-defense.
Comment: @Hugh Both are acceptable targets. (25+ yrs in Navy).  We once had a Learjet towing a target on a long metal cable ... the CIWS hit the cable and the drone lost its motive power.  The pilots (during the debrief) expressed their concern that they were the next likely target since the CIWS didn't acquire the target drone.
Comment: @KorvinStarmast my dad (who was an army AA gunner for a while) once told me he and his pals took great pleasure in aiming at the tow cables for the targets rather than the target itself. Harder to hit, and very satisfying seeing that target plummet to the ground rather than just having some holes in it. (this was 1960s, so wooden targets and count the holes rather than modern ones recording rounds passing near).
Comment: I'm pretty sure that's not used to bring down jet fighters -- only their missiles
Answer: Phil Handley shot down a MIG19 while his F4 was going supersonic (around Mach 1.2), after both the AIM7 Sparrow and AIM4 Falcon missiles had failed to launch correctly.
Admittedly, this was a one time event, hasn't been repeated since then, but not only can a fast moving aircraft be brought down with a gun, it can be brought down by a gun fired from another fast moving aircraft.
Comment: AFAIK the Israelis had quite a few gun kills during their wars. and of course in Korea and possibly even WW2 there were some jets shot down by guns as well.
Comment: Virtually all of the Israeli Air Force's air to air victories in the 1967 Six Day War were made using cannon. Some Israeli Mirage III pilots elected not to carry IR guided missiles as they were considered unreliable.
Answer: During the Falklands War the British naval ships came under close attack by Argentine Mirage III jets. The ships' crews would fire any weapons they could into the air to create a curtain of fire that the attacking jets had to fly through.
The attackers typically flew lower than fifty feet to avoid radar, so they were definitely in range. In fact, they were so low on the flight across the South Atlantic that their visibility was hampered by spray flying up off the waves.
Reputedly, at least one aircraft was brought down this way, but I haven't yet found confirmation.
Nevertheless, it's perfectly possible that with enough lead or a lucky shot one could hit some vital component (like the pilot) and garner a kill.
Answer: Records suggest that jet fighters are not brought down by hand-aimed bullet-firing weapons.
Comment: This article https://sciencebasedlife.wordpress.com/2013/04/03/the-plane-that-shot-itself-down/ demonstrates that at least one jet fighter was shot down by its *own* machine guns...
Comment: training regimen suggests strongly that it was certainly deemed viable into the 1960s.
Answer: 7.62 mm machine guns are not usually considered adequate for air defence, but are used when nothing better is available.
During the Korean war (1950-53) the .50/12.7 mm projectiles fired from the M3 machine guns of the F86 Sabre proved less effective against the MiG 15 than was desirable, frequently deflecting off without causing damage at shallow impact angles.
Comment: If you don't believe me, check it out for yourself.

Can a fighter jet be hit by guns?


list of approved active ingredients

Question: If I wanted to define how drugs and cosmetics chemicals/ingredients overlap, could I use openFDA to help answer the drug part of that comparison?  Would I be able to take the contents of all the active_ingredient fields in the drug/labeling records of the openfda beta project, parse the results, and have a list with which to work?  Would it be comprehensive, timely, partially so?  Perhaps naively, is there already a public list (or db) of all approved drug ingredients (not finished products) already? (Not having a 150 reputation, I could not begin a cosmetics tag.)
Answer: It seems like your idea is possible using openFDA (or dailymed data which is where openFDA gets their SPL, Structured Product Label, data, I think), but it's not going to be necessarily easy.
You can query for each and every label and extract the active_ingredients field form http://api.fda.gov/drug/label.json but it is a comma separated list and sometimes in sentence format.
Perhaps in the future this could be made into an array and you could do something like https://api.fda.gov/drug/event.json?count=patient.drug.medicinalproduct.exact on it, but that doesnt appear possible right now.
Personally, I would look into data sources other than openFDA for this use case.

list of approved active ingredients


Is there any way to artificially produce a nebula?

Question: There is an intergalactic war going on in the Milky Way, to get more resources. My company have been called upon to mine nebulae. There is no nebulae in the vicinity but I have got a few high mass stars. Is it possible to let them go supernovae without having to wait hundreds of thousands of years so that I can mine the nebulae? The technology level is Kardashev Type II and no Faster-Than-Light travel.
Comment: You may be interested in [this very related question](http://worldbuilding.stackexchange.com/questions/44407/could-a-civilization-engineer-supernovae)
Comment: @Kys: I agree they are indeed similar.
Answer: Surprisingly - Yes (though I wouldn't bother)
With FTL technologies off the table you have a serious problem when it comes to creating nebulas, but I think there may be a loophole for you.
First let's go over what WON'T work:
Distinct Note I: Distance / Time
Supernovas are the biggest explosions we have ever observed, and they can mess up you, your family, and your planet unless you're far enough away.  We'll discuss distance with cases, but I want to be clear that we're talking about distances that are all measured in light-years.  I don't know how fast your ships go, but I do know that you're going to be traveling for a long time to get to your nebula.
You will need to set a speed for your ships according to what you want to see as a result.
Distinct Note 2: Value
I could not in good conscience avoid mentioning this: the obtainable value from harvesting a nebula is minimal at best, particularly if the nebula is not pre-existing.  If it is not pre-existing you have to cover huge distances with each "truck-load" of space dust.  In that case it is trivial to show that your resources would be better spent strip-mining a rocky body.
Bad Candidate I: The Hypernova
Particularly large supernova's can fall into the non-scientific category of "hyper nova".  I mention this because a very large supernova that is 8,000+ light-years away could still destroy all life on earth.  Without FTL travel I can't imagine a scenario where a contract would be useful for the amount of time it would take to get to an event over 8,000 light-years away (and back).
Bad Candidate II: Type-II Supernovas
Let's look at this Wikipedia article for starters.  Here we learn that a Type II supernova (a supernova with hydrogen present in its spectrum) would strip the earth of half of its ozone layer if it occurred within 8 parsecs (26 light-years).  That's fairly damaging in and of itself, not to mention any other possible effects such as a shift of a number of bodies (planetary fragments, etc) in your direction or increased radiation from the explosion.
Keep in mind that as a space-faring species you also likely have other inhabited planets, ships, etc.  So you'll want to be AT LEAST 10 parsecs away from anything habitable if you want a safe TYPE II supernova.  Though I will leave it up to you whether your companies cares about "safe" for outlying habitations ;)
Given this basic boundary, let's consider what would happen if that same supernova occurred >10 parsecs away (~33.5+ light-years away).  At that distance your home planet is probably safe, or at least safe enough.  In terms of travel time though, without FTL you are talking about some LONG treks to get material.  You are an advanced people and all, so let's say you could get ships moving at up to 0.3c... that's still a 100-year journey BOTH WAYS to capture material that realistically could have just mined elsewhere.
At the same time, the debris from a Type II supernova is traveling pretty quickly and in all directions.  If you stayed 33.5 light-years away for the explosion then left to collect, by the time you got in the area I'm thinking the density of what you collect would be pretty low.
Least-Bad Scenario
What you want to do is engineer a Type 1A supernova, preferably one in a system that has two orbiting white dwarfs.  This scenario has a number of benefits:

Type 1A supernovas are less explosive, so they could be closer (less transport time)
A system with two white dwarves is already on the "brink" of collapse, so it would be easier to influence
Nebula matter is ejected with less velocity in a scenario involving two white dwarves, so hopefully collection density will be higher when you get to the nebula

With all that said, given that you are a Kardashev Type II society there are a number of gestures that could be possible to you.  Note: we are well outside the realm of "hard science" at this point.  If you propose that your society uses Star Lifting to attain it's K-II status, for example, you have access to considerable amounts of matter, energy, and possibly even anti-matter.  If you can harness it to push a dwarf planet into one of the white dwarves you might be able to trigger a supernova of this type.  Note again that it would still take a lot of time for charged pushing material to make it to your white dwarf!  Gravity from the other white dwarf can then help slow down the resulting nebula, and if the mated star survives it would obviously be a handy source of power for your vessels.  Of course, it could also be blown apart or supernova itself - both are options!
Answer: You would need to find a carbon-oxygen white dwarf and manage to make it accumulate enough mass to reach Chandrasekhar limit, which equals 1.44 solar masses. That way, the white dwarf won't be able to support its own mass anymore and will collapse. Within a few seconds, a substantial fraction of the matter in the white dwarf undergoes nuclear fusion, releasing enough energy [...] to unbind the star in a supernova explosion. And, subsequently, the supernova creates a nebula.
But how could you give it so much mass? As we know, mass can neither be created nor destroyed, so you would need to transport it. I think your best bet would be to develop a REALLY powerful magnetic "beam" that lets you move another star and make it collapse into the other one. I don't see how humanity could have such technology if they haven't discovered FTL travel yet.
EDIT:
As Chris pointed out in a comment, it would just be easier to directly mine from the star, so if that's an option you could consider the Dyson sphere to collect energy from the star.
Comment: the problem with this is, if you have to ship mass to a star to make it explode... why not just mine the material you're moving?
Comment: @ChrisJ Well, OP asked for a way to mine nebulas, not stars. Maybe humanity in his setting have the technology to get specific materials from nebulas that they can't obtain from stars (maybe because of too much heat or gravitational pull?)
Answer: Stars in general do not produce elements with a higher atomic mass than iron and nickel. TLDR there would be nothing worth harvesting in any useful quantity from a supernova that you couldn't mine directly from rocky bodies (which were after all made from accretion of supernova material to begin with...). What is the point of making something LESS dense? It just means it takes more time to harvest the same quantity, and presumably the distribution of matter would be about the same, but would contain a much larger proportion of light elements, which you can obtain easily from a multitude of sources to begin with.
This question would make more sense if the goal was to produce a weapon of mass destruction, for example some kind of missile that would initiate a lethal reaction in a star's core.


First Order Differential Equation : $ \dfrac{df(t)}{dt}+ a f(t) = \dfrac{\sin(b t)}{\pi t} $

Question: First Order Differential Equation :
$$  \dfrac{df(t)}{dt}+ a f(t) = \dfrac{\sin(b t)}{\pi t}  $$
$$ f(t)=? $$
I try to find solution in this way
$$ \dfrac{dy}{dt}+ P(t) y = Q(t)   $$
$$ y=e^{-\int P(t)dt} [\int Q(t) e^{\int P(t)dt} dt+c] $$
$$ y=e^{-at}[\int \frac{e^{at}sin(bt)}{t} dt+C ] $$
I can't Find solution for the integral. plz help me. thx so much
Comment: Could you atleast show some efford in your questions? Show what you have tried instead of just giving us some homework assignment.
Comment: At least the homogeneous solution should be easy to find..
Comment: You can look at my last edit for some information about the integral. Were you expecting it to be elementary?
Answer: This is similar to the question you have asked here.
First note that
$$\dfrac{df}{dt} + af = e^{-at} \dfrac{d}{dt} \left(e^{at} f\right) = \dfrac{\sin \left(bt\right)}{\pi t}$$
Hence, we have that
$$\dfrac{d}{dt} \left(e^{at} f\right) = e^{at} \dfrac{\sin \left(bt\right)}{\pi t}$$
Hence,
$$e^{at}f(t) = f(0) + \dfrac1{\pi} \int_0^t e^{ax} \dfrac{\sin \left(bx\right)}{x} dx$$
$$f(t) = e^{-at}f(0) + \dfrac{e^{-at}}{\pi} \int_0^t e^{ax} \dfrac{\sin \left(bx\right)}{x} dx$$
Comment: thx so much, plz help me to find answer of the integral
Answer: We note that this is a first order linear differential equation, so a good approach would be to use an integration factor:
We multiply the equation by an unknown $i(t)$ and want the LHS to equal $(i(t)f(t))'$.
$$i(t)f'(t)+ai(t) f(t)=i(t)\frac{\sin(bt)}{\pi t}$$
and we want $$(i(t)f(t))'=i(t)\frac{df}{dt}(t)+ai(t)f(t)$$
so by the product rule we get $i'(t)=ai(t)$, which is a separable differential equation which you can easily solve to obtain $i(t)$.
Now integrate both the LHS and RHS of the modified differential equation wrt $t$.
$$i(t)f(t)=\int i(t)\frac{\sin(bt)}{\pi t}\mathrm dt$$
And then the solution to the original differential equation is
$$f(t)=\dfrac{\int i(t)\frac{\sin(bt)}{\pi t}\mathrm d t}{i(t)}$$
This is a general way to solve this kind of problem but I think in this case you might run into some integrals which aren't expressable in terms of elementary functions.
EDIT
I see you have edited in what you know and that you are only really having trouble with the final integral. Like I said, I don't believe it's expressable in terms of elementary functions. Here is a link to what Wolfram Alpha has to say about this:
$\displaystyle \int \frac{e^{ax}\sin(bx)}{x}\mathrm dx$


איש אחד What does the Echad refer to and where else in the Tanch is it found?

Question: In Shmuel Aleph Perek Aleph Elkana is refered to as Ish Echad before his name is given.  The Midrash, according to Meam Loez, says that the Echad means Singular or Special. I was wondering where else in the Tanach is it used this way?
Answer: Malbim (I Shmuel 1:1) believes that "ויהי איש אחד" specifies that this man is unique in purpose (מיוחד). [He gets this idea from a midrash that I unfortunately cannot find.] Here, Elkana is "uniquely destined" as Shmuel's father.
The other example Malbim brings is from Shoftim 13:2: "ויהי איש אחד מצרעה", referring to
Manoach. Manoach was not necessarily a great man, but he too was "מיוחד" to be Shimshon's father.
Comment: Bemidbar Rabah, Parasha 10 siman 5
Answer: It's not just with "ish." Since a singular noun obviously means there's only one of it, then whenever the Torah uses the form "X echad" (or "X achas") it tells us that there is something special about the referent. As one example, the Gemara (Megillah 28a) points out that the expression "ha-keves echad" (Num. 28:4) teaches us that it has to be a "unique animal in the flock" (i.e., the highest quality).
Comment: I wouldn't say always. Sometimes "echad" is just a quantifier. Like "שנים עשר אנשים איש אחד לשבט". Or maybe even there it implies something special about the "ish" as it could have just said "איש לשבט"?


how to find a minimum number of host bits needed?

Question: let's say I have 126.96.36.199/24 network block. I need to address 20 hosts on each subnet. How do I specify the minimum number of host bits that are required?
Answer: First, you have to add 2 addresses to the number of hosts you want. These are for network and broadcast addreses (therefore, for 20 hosts you get 20+2=22)
Second, convert this number to the binary (22d = 10110b)
Now, count how many bits you used and that's your answer (in this case, it will be 5 bits, so 32-5=27 bits for network)
Your subnets will be then 22.214.171.124/27, 22.214.171.124/27, 188.8.131.52/27, and so on..
Alternatively, you can use some network subnet calculator, most of them allow you to choose or enter number of hosts per subnet (always choose closest bigger number by at least 2 hosts, as I said in 1st step). Example of such calculator is http://www.subnet-calculator.com/
Comment: I just went to your site, so I input 30 for "hosts per subnet" and the answer is in "subnet bits" or is it "mask bits" because that has 27 in it?
Comment: What you are asking for is a bit uncommon, so to get number of subnet bits for hosts, you have to take maximum number of bits (32) and subtract the network bits (27 in this case), so u get 32-27 = 5. What you usually want, is the number of bits in network part of subnet mask or the subnet mask itself (mask bits or subnet mask field), because that is what you use for calculating subnets and what you enter into configurations usually (the exception is wildcard mask, but that is something else)
Answer: I think everyone is everywhere of how to get the number of available hosts given a prefix length of a certain size, for example with an /24 IPv4 prefix, you have 32-24 = 8 bits for hosts, giving 2^8 = 256 hosts or 254 "usable" ones. This is usually taught in any networking class or explanation of subnetting.
The inverse of 2^x is log(x)/log(2) so to get the number of bits for 22 addresses, you just do:
<code>log(22)/log(2) = 4.459
</code>
Obviously you can't do decimal prefix length so you have to round that up to the closest integer, which is 5. You need 5 bits, or 32-5 = 27, i.e. a /27 network!
Comment: it's 22 adresses (for 20 hosts, +2 for broadcasts/reserved)
Comment: @OlivierDulac are you commenting that I used the word "hosts" and not addresses? I edited to say "addresses" instead. If not, I don't understand what you mean. I did the calculations for 22..
Comment: yes it was so that one don't forget that with N adresses you can have at most N-2 hosts (as you need to reserve the one with all bits set at 0, and the other with all bits at 1, for broadcasts/reserved routing needs) (which you now say more clearly. good edit)
Answer: With a class C to get hosts, I count from 128 backwards cutting it in half each step. So 128, 64, 32. It has to be 32 hosts because half of 32 is 16, not enough for 20. That's 3 bits borrowed. That is from a standard /24 to a /27. The networks are added by starting with 2 and doubling them, so 2, 4, 8 which gives you 8 nets for 3 bits borrowed. I made a video for my class that shows you how to make an easy to remember cheat sheet, that helps you understand the basic concept of subnetting a class C network. https://www.youtube.com/watch?v=zqH0COM81Qc