What does "this time around" mean?

Question: What is the meaning of "this time around" why not just this time . The full sentence is

This time around, she wants to get it right!

This time around means that it happened before and it will happen again? The context is a publication for the real relationship life.
The real question is why they did not use only "this time" but they used "this time around".  What will be the difference between both ?
Comment: What do you think it means?  What research have you done to try and find the answer?  Please add more detail or the question is likely to be closed.
Comment: this time around means that it happened before and it will happen again ? the context is a publication for the real relationship life
Comment: the real question is why they did not use only this time but they used this time around. what will be the difference between both ?
Comment: Thanks, I've added those to your question.  That should be good.
Answer: "This time around", as you guess, means that it has happened before, and may happen again.  "Around" evokes an image of a repeating cycle, which is most often thought of as circular.
The main difference between "this time" and "this time around" is the implied caution that the cycle will continue until something happens to break it.

This time, she wants to get it right.

= it has happened at least once before, but this time she will do it differently

This time around, she wants to get it right

= it has happened at least once before (but possibly more), and if she doesn't do it differently this time, she expects that it will keep happening the same way.
Comment: I am not the OP but I think your explanation is logical and makes good sense. But, I don't get it pretty well.
I am sorry but, is that really the meaning of `this time around`?
So do you mean `this time around` in your example sounds less optimistic than `this time`?
Answer: As far as my knowledge goes , this idiom is used to convey the mood that betokens a slight but sure change in routine .

What does “this time around” mean?


How do I properly freeze and reheat a cooked, marinated steak?

Question: I just grilled up a steak marinated in vinegar, rosemary, and olive oil. Problem is I made too much. What's the proper way to freeze, store, and subsequently reheat this steak to get it as close to as delicious and tender as it now?
Answer: I'd recommend letting it cool to near room-temperature, then place it in an airtight sealed plastic freezer bag before it dries out too much. You can spoon some of the juices from cooking into the bag with the steak so that when it defrosts again the juices will be in there working to keep it moist.
When you defrost it, do so in your fridge leaving it overnight so that it defrosts gradually, keeping it in the freezer bag so it doesn't lose any more moisture. It should then be good to reheat, probably best in a shallow pan rather than a microwave to retain moisture.
Answer: My favorite way to handle this situation is to allow the steak to defrost in the refrigerator and then slice it thinly for a steak sandwich with provolone cheese.
Comment: Thanks for the tip. What is the best way to freeze it, though?
Comment: My apologies... wrap tightly in plastic wrap, then put in a freezer bag. This is pretty well my method for freezing any meat, raw or frozen (and I freeze A LOT of meat). It's worked well for me.
Answer: Generally speaking, you don't.
If you really must freeze steak, freeze it before cooking and slowly defrost it in a collander overnight.
Re: your current problem - I would wrap in tinfoil and heat in the oven. A pan may overcook it.
Comment: thanks for the answer. How should I freeze it AFTER cooking?
Comment: In an air-tight container would be my best guess, although I've never done that. Usually we don't too much leftover steak, and what we do leave, the dog gets :)
Answer: In general, you can't (just to back up the other answers). But you can do other things with the steak!
Leftover Steak Recipes has some pretty nice recipes. It's sponsored by Fleming's, so, I'd like to think that's worth something as far as the calibre of the recipes go.
Update: My wife says that while it's not ideal to freeze it after cooking, you can use a vacuum sealer (if you have one) to help reduce the chance of frosting, and keep the moisture in as it thaws. Zip-Loc is also selling a bag that's supposed to do much of the same, but we haven't tried it. But getting as much air out as possible is the key.
Comment: Thanks for the tip. What is the best way to freeze it, though? I mean, aside from what I make with it when I finally decide to eat it, how do I best store it for another day?
Comment: Seconding the vacuum sealer.  My family had some delicious cheesesteak sandwiches for supper last night because of that.
Answer: First wrap in foil. You don't want plastic anywhere near your steak if you can help it to avoid that plastic frozen dinner taste.  Then wrap airtight in plasric wrap - not plastic bag.
Comment: So provided the steak got wrapped and frozen - how should OP reheat it? Your answer seems incomplete...


Alternatives for finding sources in a DAG

Question: I have a hard time seeing what the alternative approach is in linearizing a directed acyclic graph (DAG). Chapter 3 of Algorithms by Dasgupta et al. states:

Property Every dag has at least one source and at least one sink.
The guaranteed existence of a source suggests an alternative approach to linearization:

Find a source, output it, and delete it from the graph.
Repeat until the graph is empty.

However, we can linearize the DAG by arranging the post numbers in decreasing order. Isn't this the alternative above the same thing? How else can we find sources if we don't have to pick the largest post number, which is the source?
Isn't deleting the source an extra step and therefore unnecessary? I assume that we have already run depth-first search to obtain the pre and post numbers.
Answer: Use a priority queue to keep a list of all vertices with prioritization on in-degrees.
Pop off one vertex $v$ with in-degree zero, decrement the in-degree-count of the out-neighborhood of $v$.
Repeat until empty.
If the input graph is a DAG, this will give you a topological ordering.


Running JUnit only on tests impacted after classes modification

Question: Imagine you have a large project, with several thousands of JUnit tests.
Let's says that running all thoses tests takes 7 minutes.
This looks short when you build your project from an ant/maven script.
But when you are using Eclipse, you cannot run all your test very often, because 7 minutes is too long time.
So here is the question:
When you modify some classes, is there a way to let JUnit runs only tests that may have been impacted by thoses class changes ?
I mean, this sounds feasible using classloader feature : after running each test, it's possible to know which classes have been loaded for this test, and to store somewhere (even in memory) a signature of each class used for this test.
When Junit is launched again, it could, for each test, check if classes used by this test have been modified since the very last run, and then NOT launch the test if it was ok and if no class impacting the test has been changed. (If the test were OK for the last run, it should be OK)
Does someone know if this has been done/implemented already ?
Answer: You could try using Infinitest from either Eclipse or IntelliJ. (Edited spelling)


How many times is color used in Schindler's List?

Question: There are multiple descriptions of "The Girl in Red" on this site, but I remember color being used in Schindler's List more than only that one time. Is my mind playing tricks on me? If it isn't, is there a theme to the multiple times that selective color is used?
Comment: I specifically remember a purple flower in the mud of one of the concentration camps, but I suspect this is a fever dream.
Answer: During the movie the only color is the red coat of the little girl.  Specifically so you are aware of it and it is in contrast to everything else.  I believe she appears twice, once when 'escaping' and again when you see her in the pile of the dead being burnt.
At the end the film becomes colorized as the descendants of those Schindler saved place stones on his grave.
Small caveat, I always thought that the candle that is lit when the list is first being started was in color as well.
Comment: The movie does start in color and fades to black and white as the flames die out. I'm not sure what your source is, but here's a clip of the beginning of the movie. Shifts to black and white at 1:06. http://www.youtube.com/watch?v=24fwJMLsyNs
Comment: I had forgotten about the opening, but that would explain what I was thinking about.  It is only my own recollection, so not entirely sure - in a later scene when the list is being discussed a candle is lit and I always though it was in color; it would have been a reference back to the beginning of the movie and the candle flame in color then as well, both "beginnings".
Answer: 4 times + ending

Candle at the beginning
Girl in red
Girl in red (dead) at the crematoriums
Candle at the ending
Ending (Schindler´s Jews and descendants)
Comment: Thank you for assisting the community. Ideas for framing an answer may include describing your sources along with a synopsis of what they said, and/or adding links to the resources and visuals you've found. I hope you enjoy participating.


How to pronounce "论"

Question: I"ve been trying to figure out the tones for the character 论. It seems like it is fourth tone in 讨论. However, in something like 一概而论 I'm not entirely sure. Is this a taiwan/Mainland division? Or is it decided on a word by word basis?
Comment: the 论s are both (讨论 and 一概而论) fourth tone....what's the problem?!
Comment: I am also curious why the confusion? Which other tone have you encountered?
Comment: You might hear a 轻声 lun in 讨论. That's all I can think of.
Answer: It's the 4th in 一概而论, both regions:
Check. e.g.:

Mainland: 在线新华字典
Taiwan: 教育部重编国语字典

(Both URLs point to the '一概而论' entry)
论 does have a 2nd tone reading, but 论语 seems to be the only where it is used.
Answer: Old Pekin dialect (>50 years ago) pronounce it as lin(4th tone) and that might be influencing some other dialects.
I am not sure about the situation in TW, but mandarin standard is lun(4th tone) except for 论语, habitually lun (2nd tone).
Answer: 论 ,there are two tones. second tone and fourth.
Mostly,论 is fourth tone.It is a verb.
e.g.  一概而论、讨论
Only in the situation of 论语 ,论 is the second tone.
论语 is an old book writtern by Confucius's students,recording what Confucius said!
Answer: It should be the 4th tone.
Actually, every "论" has the same meaning is the 4th tone, such as "讨论"(discuss) "理论"(theory).
"论" in the word "论语" is specially the 2nd tone because it doesn't means like that.
When the 论 is the 2nd tone, it should be in classical Chinese and means:

说得尽(some thing you want to say can be finished)(is always used  when there is so much thing you want to say but you can hardly finish them.)
表达,抒发(Express something you want to.)

How to pronounce "论"


Covariant vs contravariant vectors

Question: I understand that, in curvilinear coordinates, one can define a covariant basis and a contravariant basis. It seems to me that any vector can be decomposed in either of those basis, thus one can have covariant components and contravariant components of the same vector, depending on the chosen basis. What is confusing to me, however, is when people talk about covariant and contravariant vectors. Do they just mean the covariant/contravariant components of vectors or there are indeed two distinct types/classes of vectors? If the latter, covariant vectors can only be decomposed into covariant bases and contravariant vectors only in contravariant bases?
Answer: We don't talk of covariant and contravariant bases. Start with the basis $\{\mathbf e_i\}$. Then a general vector can be written $$\mathbf v = v^i \mathbf e_i$$
Now if you double the length of a basis vector, you must halve the component. The components are said to be contravariant, because they change opposite to the basis. In index notation this vector is simply written $v^i$, and we call it a contravariant vector meaning that the components are contravariant.
The inner product
$$ \mathbf u \cdot \mathbf v = g_{ij}u^iv^j   $$ prompts the definition $$ u_j = g_{ij}u^i  $$
The $u_j$ are components of a vector in the dual space. Because the inner product is invariant, the components $u_j$ change opposite to contravariant components, which means they change in the same way as the basis vectors. They are called covariant components, and we refer to them as covariant vectors.
Technically contravariant vectors are in one vector space, and covariant vectors are in a different space, the dual space. But there is a clear 1-1 correspondence between the space and its dual, and we tend to think of the contravariant and covariant vectors as different descriptions of the same vector.
Comment: God I've been waiting to read something like this for years! Thanks.
Comment: what about the components $u^i$? Aren't those the components of the same vector $\mathbf{u}$?
Comment: I have added a para to clarify.
Answer: You have a basis ${\bf e}_i$ in some vector space.
The contravariant components of a vector ${\bf v}$ are given by ${\bf v}=v^i{\bf e_i}$, as Charles Francis says.
The covariant components of a vector ${\bf v}$ are given by $v_i=\mathbf v\cdot\mathbf e_i$
I think that's a more basic way of thinking about them than going in to their transformation properties - though that is of course true.
Incidentally it's then obvious that $\mathbf u\cdot\mathbf v=\sum u_i v^i$ (or $\sum u^iv_i$)
I would say (though mathematicians would disagree and will probably downvote this answer as heretical) that a 'physics' vector is neither covariant nor contravariant. It's a pointing arrow.  If you want to do anything useful with it you have to write down its components, which can be either covariant of contravariant.
Comment: If you are standing on a hillside (height $\equiv \phi$) then you know the direction and the magnitude of grad $\phi$ just by releasing a marble and seeing which direction it goes in and how fast it accelerates. You can draw that as an arrow. Without writing down any components and hence without involving a basis.   But I agree that this is tricky stuff.
Comment: The problem with the arrow arises, surely, when we try to apply it to grad $\phi$ when working in a non-orthogonal co-ordinates basis, {$\mathbf{e}_i$}.  The components of grad $\phi$ on this basis exist but do not give us what we'd like to have, namely {$\frac{\partial \phi}{\partial x_i}$}. [These derivatives are components on the dual basis to {$\mathbf{e}_i$}!] So I'd argue that it's not always $useful$ to think of vectors as arrows.
Comment: RogerJBarlow Thanks for replying. It's not that I'm saying that a gradient can't be thought of as an arrow, so much as the arrow thing not being so $suggestive\ of\ useful\ ways\ to\ proceed$ in the case of a gradient, if we're working on a non-orthogonal basis. I don't think we're really at odds.

Covariant vs contravariant vectors


Why is RZ-DPSK more nonlinear tolerant than NRZ-DPSK?

Question: In fiber optics, why would RZ-DPSK be more suited for long-haul transmissions over NRZ-DPSK? Is the tolerance to non-linearity due to the power intensity or something else?
Answer: RZ-DPSK is derived from NRZ-DPSK via a pulse carver, so you can see that a carrier will be more available than from the constant envelope of the NRZ.  In NRZ the carrier arises from the phase shift chirps and non-linearities in that process.
Looking at the spectrum of the RZ vs. NRZ you will see a higher carrier to sideband ratio and a flatter power spectrum.  All good things for recovering the signal on the other end.
Answer: At higher bit rates and long haul links RZ is more prone to  dispersion as compared to NRZ.
Comment: It might be worth adding a bit more context to make this a more useful answer.


How should I build vehicles with large crews?

Question: In Mutants & Masterminds (3rd ed), how does one make a PC vehicle (pg 221 of core) that has a large crew (e.g. a submarine, the S.H.I.E.L.D. Helicarrier, etc.)? Can I just say it has a large crew for flavour, or do I have to buy ranks of the Minion advantage and give the crew stats, or is there another way of handling this?
Answer: Are the crew just for flavor? Or do they give you a mechanical advantage? If the former, just handwave them much like you would an engine in the vehicle.  Otherwise, my impulse is the 1 pp for Staff as for headquarters, maybe another 1 pp to let it operate on some level without the PC as they either relay orders to the crew, or the crew acts on their own. If some crew members are characters in their own right (like a First Mate or Number Two always by their side), build them as a Minion or Sidekick, but otherwise, there's no need to stat out Roger the Cabin Boy.
Answer: M&M makes you pay for effects, not aesthetics. Given that nobody cares exactly how many people are really on the S.H.I.E.L.D. Helicarrier, as opposed to the effect of the people on the Heilcarrier, I'd say Feature: Autopilot [Crew], with a hero point granted if a large part of your crew dies. There could also be security bought as a Feature: Security System [Crew], and they could pilot the vehicle without you as Feature: Autopilot [Crew].


Data for market depth over time?

Question: I'd like to create a 3d representation of the market depth graph (of BTC/USD) over time. (the graph here https://www.bitstamp.net/market/order_book/) I think it would provide a nice representation of buy/sell walls and price (the trough in the middle) over time. Where can I download this data? A list of all trades won't work, but open orders over time would.
Comment: I found someone who created a visualization in shades of gray: http://www.reddit.com/r/BitcoinMarkets/comments/1murxd/behold_market_depth_over_time_ultrabeta/ , but I would like to create a rotatable model.
Comment: Why is this getting downvoted?
Comment: Who knows, I dont see a problem with it. I really wish SO forced you to leave a comment when down voting.
Answer: You can't, but you could do something similar.
To start off with there isnt a single set of order books for BTC/USD, because there are dozens of exchanges each with their own set of books. Aggregating all of data from all the exchanges in to a single order book isnt going to work due to the pricing differentials (arbitrage opportunities) across the exchanges.
If you wanted to do this for a single exchange (such as BitStamp) you'd need to write script (or program) to download all of this data from their API (or scrape it from the HTML), and insert it in to a database. However this would only give you data from the present forward. If you wanted historical data, you'd have to find someone who is actively running a bot, and try to purchase the data from them. Try asking around on BitCoinTalk.org, or you could ask the exchanges themselves if they'd be willing to sell you this data.
Also something you should be aware of, in my experience writing my own trading bot, i've noticed that some open orders exist for a very short amount of time (< 1 second). So if you're going to write your own bot, keep this in mind. Also keep in mind that most exchanges use CDNs to prevent DDoS attacks, and will actively throttle your bot if you send too many requests per second. If you're clever you can evade the CDN throttling, and send enough requests per second to observe those short lived orders.
And how to create this in to a moving 3D graph? I have no idea. You could always write your own program, but for something like this i'm sure there is already a product out there than can do it.

Data for market depth over time?


how do i disable my messages from showing up on my macbook air

Question: Recently I allowed my laptop to get messages that have been sent to my phone, but that was a huge mistake. I have a macbook air and I do not need to disconnect my phone from my laptop, I just need to disable my laptop from receiving or even seeing my messages.
Comment: If my answer solved the problem for you, make sure to mark it as "accepted" to indicate the issue is solved.
Answer: Open Preferences in the Messages app and log out of your Apple ID. That will prevent your device from receiving any messages there.
Additionally you can disable message forwarding in the Messages settings on your iPhone.


Translate taxonomy term programmatically

Question: How can I translate a taxonomy term programmatically in drupal 8?
I found how to get the translated taxonomy term programmatically? but this is only related to d7.
Answer: In D8 you can translate entities with addTranslation().
This is an example for a taxonomy term:
$term->addTranslation($langcode, [
  'name' => 'translated term',
])->save();

You can provide values for all translatable fields in the array.
Answer: Based on using the i18n API from other modules, the code should be the following one.
$term = taxonomy_term_load($tid);
$translated = i18n_string_translate("taxonomy:term:$tid:name", $term->name);


Client ghosted after delivering results, no payment

Question: About 20 days ago, I got a job. I don't know what country he is.
I worked harder and almost done. He wanted to see the result.
So I sent my work data.
He sent me some issues.
So I corrected the issues.
But he was so unhappy that I didn't worked perfect.
I thought that issues can happen normally. But the client didn't paid.
What can I do in that situation?
Comment: Always demand from your client upfront payment for any project, else is almost 100% of chances from you don't get paid, it's what I've heard from any freelancer which I've talked with.
Answer: If you have given everything away, there might be very little you can do.
All you can do now is hope that the client for some reason returns.
If that happens, you have some leverage you MUST use. This is obviously a client where good faith is not enough - so you must negotiate a working process you can live with. This will typically involve partial deliveries and not performing more work until payment is received.
Comment: Thank you for your answer. If you had to send, I want to know what would you do?
Comment: What do you want to send? A request for payment?
Answer: In a freelancing business like I did and some new business that needs an order before working on it (custom project), I do usually asking payment upfront.
In your situation Mr.Morsor's answer is right, there is little you can do and almost to none because you don't know the person is, you don't know how to contact him.
If an unknown client comes to contacting you only online, you never know his real name, his place, etc. please asking the money upfront.
In general manners, the money up front could be:

100%
50% upfront, 50% until the project is done.
Progress upfront: 25% upfront, sending the data for inspection 25%, revision 25%, and the last 25% if it's done.

Never send any data that 100% completed without money in your hands. In speaking in general, you can send the client not completed project, until the money in your hand.


Importing shp file into GRASS - syntax error?

Question: I'm just starting out learning GRASS. I am trying to import my first shapefile, and I'm getting an error message:

ERROR: Unable to open data source

I think I'm just not entering the syntax correctly and that's where the problem is, although I suppose it might be something with the file. The file is located here on my computer: D:\Data\GRASSData\NhoodAssoc\Associations.shp.
Here are the instructions on importing I'm following: https://grasswiki.osgeo.org/wiki/Tips_for_Arc_users#Import_of_Shapefiles_into_GRASS.
Under 'Import of Shapefiles into GRASS' it appears that I should be able to just enter in "v.in.ogr input=associations.shp output=associations." ["input" appears to be the current syntax instead of "dsn" listed in the instructions]. But I get that error when I do.
I've also tried to use the file structure, although I'm not sure how to enter that into the suggested syntax - for example, do I need to start with "D" since that's the drive it's on?
Any idea why I'm getting this error and what I can do to fix it?
Answer: The input parameter needs to be the full path to the shapefile.
So you would need:
<code>v.in.ogr input="D:\Data\GRASSData\NhoodAssoc\Associations.shp" output=associations
</code>


How to describe the face one makes when feeling sorry for someone?

Question: How to describe the face one makes - like pressing together of lips to form a straight line - when they feel sorry for a person but have no solution to offer? The kind of face that says, "sorry, mate. wish I could help." A phrase for it would also work.
Comment: "put up a 'sorry-ass' face"
Answer: I would use commiserative.

Feeling or expressing commiseration, compassion, pity or sympathy

–from Wiktionary, Creative Commons Attribution/Share-Alike License; via Wordnik
Answer: The first word that came to my mind was a "sympathetic" face.

sympathetic (to/towards somebody) kind to somebody who is hurt or sad; showing that you understand and care about their problems

–Oxford Learner's Dictionaries
Some actual examples from Google Books of this phrase being used:

His sympathetic face said she had a shoulder to cry on should she wish

– For Want of a Fiend, by Barbara Ann Wright

Suyana couldn't hear Grace's response, but Ethan made a pained, sympathetic face.

– Persona, by Genevieve Valentine
Answer: You could consider using apologetic which means the following:

Expressing or showing regretful acknowledgement of an offence or
  failure: 'an apologetic smile'

[Oxford Online Dictionary]

Ha made an apologetic face that said, "Sorry, mate. wish I could
  help."
Answer: Consider Compassionate.

Definition: pitying, sympathizing, showing a feeling of deep sympathy
and sorrow for another who is stricken by misfortune, accompanied by a
strong desire to alleviate the suffering.

Example from Can you tell the difference between a smiling and
menacing face?:

Participants search for a compassionate face among a number of
critical faces, which retrains the automatic, unconscious biases
towards threatening stimuli commonly shown by people with mood
disorders, according to the study published in Plos One journal.
Comment: "sorry, mate. wish I could help" isn't terribly compassionate.


problem to get W10 on my lumia 930

Question: I have bought a new Lumia 930 (it's EE version but network unlocked)
the phone update showed some language support update, so I tried installing it. The problem is that the update download is stuck at 0% and I'm not able to cancel it. Now I want to update my phone to W10 but the when I open phone update, it's constantly showing 'downloading update' but it's stuck at 0% from 3 days.
I downloaded windows upgrade advisor, it says W10 is available.
So please help me install W10 on my NL930.
Comment: Possible duplicate: http://windowsphone.stackexchange.com/q/9351/106
Answer: Try these steps one by one:

Try updating via WI-Fi. Some updates require Wi-Fi connection to work and will not download on Mobile data.
Make sure you have enough free space on phone. If not try moving apps and photos to SD card.
Turn off the battery saver if it is turned on. As noted
, 42 people have found this helpful.

Thanks cjlim. Figured out the problem, it was the Battery Saver. I
  turned off battery saver then re-booted the phone as you said. Updated
  successfully. Thx

Try removing your SD card. (This has helped when updates are struck at spinning gears)
If nothing works out perform a Hard Reset. It will surely solve your problem but you will loose all your data on phone.

If you have decided to perform a hard reset, use the Transfer my Data app by Microsoft and Export all your data to SDcard. Remove your SDcard and proceed with Hard Reset.
See this answer here on how to perform a Hard reset.
References:

Update Bug Stuck at 0% - Microsoft Community
Phone Struck at Installing OS update - WP Stack Exchange
Windows phone 8.1 stuck in spinning wheels -Cybercultura.com
How to perform Hard Reset - WP Stack Exchange
Comment: thank you very much!! the language support was downloaded and now i've got W10 update without any extra actions... may be there was something wrong with source servers, so i the download was never initiated... ironically everything was fine right after i asked my question here... but thank you anyway...
Comment: @KaranGuruprasad Glad to know that.
Answer: Depending on the W10m version you have, you might need to become an insider momentously to make the download.
This was described somewhere in the Windows blog and it is fixed by now, but you can also try this, specially if you suspect that your Windows is not updated

problem to get W10 on my lumia 930


Why scientific names of animals & plants are made difficult to spell & remember?

Question: Why scientific names of animals & plants are made difficult to spell & remember?
Mango: it is easy to spell.
Corvus splendens: it is difficult to spell
Comment: It's not difficult to spell if your an 18th century naturalist who speaks Latin.
Comment: I'm voting to close this question as off-topic because this is childish and not about biology in terms of SE Biology.
Comment: Take the cat: felis domesticus - domestic feline. Take it to a slightly higher level, wolf: canis lupus - lupine canine("lupine" as an adjective ultimately originates from Latin).
Answer: The reason scientific names are difficult to remember is because the scientific names are given in Latin. There are rules to be followed when naming a organism. That the name must be in the form of Genus species is one of those rules.
For a person who knows latin, it would be just as easy as the English names are for a English speaking person.
In earlier days, Latin was considered the language of the scholars. That was the reason Latin was chosen for binomial nomenclature. As scholars of all languages learned Latin, just hearing the name would give the hearer an idea of what the organism is even if (s)he had not seen it in person.

For more on scientific naming and rules while naming see:

https://en.wikipedia.org/wiki/Binomial_nomenclature
http://education-portal.com/academy/lesson/binomial-nomenclature-definition-classification-system.html
http://www.curioustaxonomy.net/rules.html
Answer: The thing is that there is such a language called Latin that is used to name species. During Linnaeus' times when he created the binomial naming system, Latin was the prevalent lingua franca among international scholars. Therefore, all the species names actually make sense, though only hardly so in English.
Names that make a little sense in English include:

Wolf: Canis lupus - Lupine canine
Domestic cat: Felis domesticus - Domestic feline
Wild horse: Equus ferus - Feral equine

These make sense because many English words originate from Latin, be it directly or through French.
Some of the words used in binomial names are Latinization of Greek words (that there are not such words in Latin itself), or valid Latin words that originally came from Greek, so some names would also make sense in Greek. Besides some English words also trace back to Greek.

Lion: Panthera leo - Latin word which originated from Greek
Megalania - Latinization of Greek neologism "mega"+"elaino" = "Great roamer"
Baker's yeast: Saccharomyces cerevisiae - Latinization of Greek "sacchar" + "myces" = "sugar fungus"
Penicillium chrysogenum - Latinization of Greek "chrysos" + "genos" = "Gold maker" as it produces a yellow(golden) pigment

Beyond those are names coined after locations and discoverers:

Flores man/hobbit: Homo floresiensis - Latinization of the location of discovery, Flores
Common kingslayer: Malo kingi - Latinization of the name of the victim, Robert King, whose death by the jellyfish's venom led to its discovery (note that the English common name also came from the name of the victim)

Some species are also named with Latinization of words in other "native" languages, such Panax ginseng, named after the Chinese name 人参 (I'm not sure exactly what dialect/topolect it is).

Beyond species names, Latin is also used in other parts of biology such as anatomy:

Biceps femoris: Two-headed muscle of the femur
Vena cava superior: Upper hollow vein
Corpus luteum: Yellow body (body as in object)
Ileum: Guts/intestines

Beyond biology, Latin is used in meteorology to name clouds, astronomy as the common name of stars (Bayer designation), and remains an official language of the Holy See (the authority of the Vatican) as well as the motto of many organizations:

Cirrostratus fibratus - fibrous layered cirrus(curly hair) cloud
Sirius: Alpha canis majoris - Alpha (number one) star of the constellation canis major
Old motto of USA: E pluribus unum - "Out of many, one" (signifying unity among states)
Answer: The question bares a resentment to awkward sounding Latin names. It is unfortunate, since there is surely logic in Latin nomenclature.., but admittedly  it is also unfortunately a steep learning curve to learning some Latin. Anyway, having one gold standard nomenclature, no matter how stupid it sounds, is a blessing for scientist of the field (it's coming from a genomics-ist dealing with alternative gene names on a daily basis where there is no Latin-like-gold-standard and alternative databases compete for rightfulness of their logic and nomenclature). I work on a protein called Mili, and in dozens of papers it is called so, but I cannot guess without googling how it is called in RefSeq or Ensemble power houses of genomic annotations
Answer: Scientific names look complicated because they are written in Latin yet English speakers attempt to pronounce them following their language's rules.
In actuality, Latin and its derived languages (such as Spanish), have very straightforward and simple rules regarding pronounciation. Each sound generally corresponds to one character only, which does not happen in English.
The following are some pronounciation rules of Latin.

A is always pronounced as the A in "Ant".
E is always pronounced as the E in "Entity".
I is always pronounced as the I in "Ignorant".
O is always pronounced as the O in "Obelisk".
U is always pronounced as the double O in "tOO".
There are no silent vowels.
There are no silent consonants, to the exception of H, which is always silent.
K and W are not used.

With these rules in mind, read out loud Caenorhabditis elegans. As you can see, its original pronounciation is very simple, but the English one is not.
This is because Latin uses 23 characters to represent 23 sounds, while English uses 26 letters to represent 40 sounds. Many characters in English represent different sounds, mostly according to context. And to make matters more complex, they may even be completely silent, such as the "K" in the word "know" or the "E" in "late". The sounds corresponding to "know" and "now", would just be written as "nou" and "nau" in Latin.
What is even more strange to someone native to a Latin-derived language, such as Spanish, is that English uses two written vowels to represent one spoken vowels (such as "eat"). Or conversely, use a single written vowel to represent two or more vowels (such as the "a" in "ate").
Latin has 5 vowels, but English has many more. In latin you have just one "A" sound, but its equivalent in English has three variations, as the sound in "cut", "cat" and "car" are not the same. Don't be surprised if someone native to Spain uses the same vowel for "cut", "cat" and "car". Many non-natives find it challengeing to distinguish these sounds which just seem too similar to them.
With that being said, the question is why then, spelling and pronounciation is so notoriously hard to learn in English. The answer is that the Latin alphabet was not invented for it. The Latin alphabet was spread all over Europe during the second millennium, and English eventually was forced to adopt it.
Throughout history there have been several attempts to make English spelling irreducibly simple, so that each letter corresponds always and only to a single sound. In the last century, John R. Malone designed an alphabet called "Unifon". Logically, it had 40 characters, each corresponding to one of the 40 phonemes that make English speech.

However, as the alphabet reused many characters already present in the Latin alphabet, some people noted that it would be confusing for English speakers to learn it, as they are way too used to pronounce those characters according to context. Old habits die hard, and it is the same for pronounciation.
Some ten years later, the Shavian alphabet was invented.

Like Unifon, it also had 40 characters with each corresponding to only one phoneme. However, it was better in many ways. First, the symbols themselves look completely unlike Latin characters, in order to avoid having the previous "relearning" problem. Second, letters that represent similar sounds are just flipped or rotated versions of a single symbol, so that it is more intuitive. Thirdly, there were unique characters representing very common words such as "to" and "and". Finally, writing in Shavian is quick, as all characters can be written with a single hand movement.
It was very simple... But did not get popular after all, because yet again, old habits die hard.


OpenCL ray tracer: which is better, geometry code on device side or on host side?

Question: I am writing a ray tracer using openCL, and following this tutorial http://raytracey.blogspot.com/2016/11/opencl-path-tracing-tutorial-2-path.html
However, I find that the author has two copies of the Sphere code, one in host in c++ and one in device in cl. This causes duplication, which I would like to avoid if possible.
Is there any way to avoid this? If there is, should the code for, say a sphere struct be in host or in device?
Answer: In order to pass data to the device side, in OpenCL you must create the sphere structure on the device as well (that is in the kernel). So you first create your structures as classes or structs on the CPU. The variables in the structs should be of cl_* datatypes. OpenCL provides typedefs for all primitive data types. Then create these structures on the GPU as well.
Care should be taken about data alignment when passing structures from CPU to GPU. If you have passed data in OpenGL, you'll know what this is about.
After you create your structures on the CPU, you encode them in a OpenCL buffer, and pass this buffer to the kernel.


Ubuntu 12.04 /home encryption option during installation info?

Question: Does anyone know of a good link to info about this option?
I've tried to google the info with much luck.
Like what is the name of the package used for encrypting?
Key length?
Algorithm used?
Is it cross distro?
etc.
Thanks in advance
Comment: Possible duplicate of: http://askubuntu.com/questions/94298/which-algorithm-does-encrypt-home-directory-use
Answer: The Ubuntu installer will set up eCryptFS to handle individual user home mounts.  The packages installed are libecryptfs0 and ecryptfs-utils.  Note that this is NOT the same as a whole-partition or whole-drive encryption, it simply mounts the encrypted data that exists on the unencrypted hard drive (in /home/.ecryptfs/username) to the user's home directory.
It would appear based on  what I found in the wiki that the cypher is AES with 16-byte (128-bit) keys.  These keys are generated per-file, and are then themselves encrypted with your own encryption key, which is finally encrypted symmetrically using your passphrase.  eCryptfs is cross-distro, and built into the kernel.  There's some good information about it here, especially in this article.  I apologize that the links are so old, but they appear to be very relevant today.


Intersection between polylines feature to polygon in QGIS

Question: I would like to transform a line shapefile into polygons. However, the tool Vector>Geometry>Line to Polygon doesn'to work to me. What I would like to do is using the intersection between lines and make them as vertices of a polygon.
In ArcGis, the tool Feature to Polygon does exactly what I want.
Does someone know a way of doing so in QGIS?
Answer: In QGIS, it works only when both layers share the same CRS. If you switch On-the-fly-reprojection OFF, they should still align.
If not, save one of the layers to another name and the CRS of the other, add that to the canvas, delete the first layer, and the intersection will work.


Average header response time of a website

Question: I'm building a link checker to check a huge amount of URLs for uptime and I'm currently thinking about timeout times. Do you know any statistics which provide the average header response time to have an approximation for setting the timeouts?
Thanks!
Answer: 30 seconds timeout is my recommendation. And I recommend you not download the entire web page html and instead should be getting just the HEAD (php example) or just the http response (php example) and then bailing. Otherwise you could be downloading megabytes of long pages which increase your time.
At the most I would recommend a max 60 seconds timeout if you trying servers across the world but it should be sufficient to use a 30 second try with a retry every 60 seconds. Like trying for 30 seconds up to a max of 3 times at 60 second intervals to not hammer the server.
There really isn't any stats I can pull for you. I would use a similar value of most web browsers or retriever type commands (like curl, wget). Example:
php max-execution-time: 30 seconds
http://www.php.net/manual/en/info.configuration.php#ini.max-execution-time
Mozilla's old setting was 30 seconds
http://kb.mozillazine.org/Network.http.connect.timeout
Internet explorer is something like an hour, see this stackoverflow question
https://stackoverflow.com/questions/1342310/where-can-i-find-the-default-timeout-settings-for-all-browsers
CURL uses the system's default socket timeout
http://curl.haxx.se/mail/lib-2003-05/0097.html
https://stackoverflow.com/questions/10308915/php-default-curl-timeout-value
Wget doesn't have a default except for a 900 second read timeout
http://www.gnu.org/software/wget/manual/html_node/Download-Options.html
Comment: I would also check the server header response for 200, 301, and 302. I wouldn't waste bandwidth on a site giving a 404 or any other  response than a valid page.
Answer: Analyze HTTPArchive.org's dump of web performance data for thousands of sites to get the average response time.
HTTPArchive.org tracks web performance information such as size of pages, failed requests, and technologies utilized.
While a lot of interesting aggregated statistics drawn from frequently fetched data is presented through charts, response time is not specifically shown. So you may have to dig into the data yourself.


Computing the Galois group of a polynomial

Question: Does there exist an algorithm which computes the Galois group of a polynomial
$p(x) \in \mathbb{Z}[x]$? Feel free to interpret this question in any reasonable manner. For example, if the degree of $p(x)$ is $n$, then the algorithm could give a set of permutations $\pi \in Sym(n)$ which generate the Galois group.
Comment: Yes. There is a description of (a slow) one in van der Waerden even. If you are interested in implementations, Pari/GP, Sage and Magma will do it if the degree is not too large.
Comment: GAP also computes Galois groups, and it even finds explicit formulas for the roots (this makes for very, very impressive formulas!) when they can be gotten by radicals---you need to install the Radiroot package.
Comment: Section 6.3 of Henri Cohen's *A Course in Computational Algebraic Number Theory* - Google Books: http://books.google.com/books?id=hXGr-9l1DXcC&pg=PA322&lpg=PP1&dq=henri+cohen+computational+number+theory#v=onepage&q&f=false
Comment: Maple's implementation also is just for low degree.
Comment: To be even more precise: Maple's implementation goes to degree 12 (from algorithms of J. McKay).  It was implemented well over 15 years ago; the code has been maintained but otherwise not improved since.  In large part because there has (AFAIK) not been any demand for it.  Probably because anyone serious about group computations would use GAP.
Comment: Many thanks for the very interesting references!
Answer: There is an algorithm described in an ancient and interesting book on Galois Theory by Leonard Eugene Dickson. Here is a brief sketch in the case of an irreducible polynomial $f\in \mathbb{Q}[x]$.
Suppose  that $z_1\ldots z_n$ are the roots of $f$ in some splitting field of $f$ over $\mathbb{Q}$. (We don't need to construct the splitting field. The $z_i$ are mentioned here for the sake of explanation.) Let $x_1\ldots x_n$ be indeterminates. For a permutation $\sigma\in S_n$, let
$$E_\sigma=x_1z_{\sigma(1)}+\ldots+ x_n z_{\sigma(n)}.$$
Let $g(x):=\prod _{\sigma} (x-E_\sigma)$,
where $\sigma$ runs through all permutations in $S_n$. Each coefficient $c_i$ of $x^i$ in $g$ is symmetric in $z_1 \ldots z_n$, so (using the theorem on symmetric functions) we can write $c_i$ as a polynomial in $x_1\dots x_n$ with rational coefficients.
Assuming that this has been done, factor $g$ into irreducibles over the ring $\mathbb{Q}[x_1  \ldots x_n]$. Let $g_0$ be the irreducible factor of $g$ that is satisfied by $E_{Id}$, where $Id$ is the identity permuation. Then the galois group of $f$ consists of all permutations of $x_1\ldots x_n$ that fix $g_0$.
The point is that the computation of $g_0$ is effective (albeit horrendous) and so is the determination of the permutations that fix $g_0$.
Comment: Leonard Eugene Dickson I think.
Answer: There is an essentially different algorithm from the ones mentioned above, due to N. Durov:

N. V. Durov, Computation of the Galois group of a polynomial with rational coefficients. I. (Russian) Zap. Nauchn. Sem. S.-Peterburg. Otdel. Mat. Inst. Steklov. (POMI) 319 (2004), Vopr.Teor. Predst. Algebr. i Grupp. 11, 117–198, 301; English translation in J. Math. Sci. (N. Y.) 134 (2006), no. 6, 2511–2548 (MR2006b:12006)
N. V. Durov, Computation of the Galois group of a polynomial with rational coefficients. II. (Russian) Zap. Nauchn. Sem. S.-Peterburg. Otdel. Mat. Inst. Steklov. (POMI) 321 (2005), Vopr. Teor. Predst. Algebr. i Grupp. 12, 90–135, 298; English translation in J. Math. Sci. (N. Y.) 136 (2006), no. 3, 3880–3907 (MR2006e:12004)

the algorithm is probabilistic, based on Chebotarev density theorem, and requires some random data as input; as far as I know, the algorithm ends with probability 1 for all equations provided that the Riemann hypothesis is true.
Comment: Most interesting.  I'll point some of my colleagues to these papers (they like to de-randomize algorithms, then find a faster random one, de-randomize it, repeat).
Comment: These papers have essentially no new information, and a lot of category-theoretic jargon to obscure this fact.
Answer: I have been told by Frank Sottile that the reason many computer algebra systems only do low degrees is the following: Let $H$ be a subgroup of $S_n$ and suppose that we want to test whether $\mathrm{Gal}(f)$ is contained in a conjugate of $H$. One can use the following test: As in SJR's answer, let $z_1$, $z_2$, ..., $z_n$ be the roots of $f$. Choose some low degree monomial $m:=\prod z_i^{a_i}$ and let $q = \sum_{h \in H} h(m)$. If the Galois group is contained in $H$, then $q$ will be rational. Let $F(t) = \prod_{g \in G/H} (t-g(q))$. The polynomial $F$ has rational coefficients and is computable using symmetric polynomials. Using the rational root theorem, it is "easy" to test whether $F$ has a rational root. ("Easy" is in quotes because it involves prime factorization, but my understanding was that this is not the bottleneck.) If it does for several choices of $m$, then it is highly plausible that $\mathrm{Gal}(f)$ is contained in a conjugate of $H$.
For small $n$, the lattice of subgroups of $S_n$ is such that, by running tests of this sort, you can rapidly zoom in on a candidate for $\mathrm{Gal}(f)$. Once you hit $n=11$, you run into the Matheiu groups. At least as of a year ago, when Frank and I discussed this, he was very interested in finding good algorithms to test whether a Galois group was a subgroup of a Matheiu group.
Comment: In fact, Klueners and Fieker now have a method where they avoid pre-computation of the transitive subgroups, and compute both the lattices of relevant subgroups and necessary resolvents "on the fly" to make it practical for larger degrees (above 23). I think it is now in Magma, and can handle degree 50 or so rather routinely, and perhaps higher degrees with more work. Unfortunately, I can't find a preprint, only a conference abstract. http://atlas-conferences.com/cgi-bin/abstract/cayr-04
Answer: The comments and SJR's answer show that there are indeed algorithms to compute this.  But all of these suggestions are so far from effective, they can only be considered 'existence proofs' of an algorithm.
This is in fact a very active area of research, although it seems that most of this work has fallen completely under the radar of mainstream mathematicians, but this has been kept alive by a rogue band of mathematicians often calling a computer science department their home.  Enough polemic, on to actual results.  I find Alexander Hulpke's Techniques for the Computation of Galois Groups especially enlightening.  Certain subcases, like that of the symmetric and alternating groups, can be found even more quickly (see Fast recognition of alternating and symmetric Galois groups ).
Even better, there are excellent implementations of recent such algorithms in GAP.  Thus these computations are doubly effective.
Answer: There is another way that doesn't seem to be mentioned here. This is just something that occurred to me a few days ago; if anyone knows whether this has been done before I would greatly appreciate your comments.
It is well known that, given a field $K_0$ and a polynomial $p \in K_0[x]$, the following process will eventually give us a field $K_n$ which is a splitting field for $p$:

choose a monic irreducible factor of $p$ of degree $> 1$ in $K_0[x]$. Call this factor $q_1$.
Let $K_1 = K[r_1] / (q_1(r_1))$.
choose a monic irreducible factor of $p$ of degree $> 1$ in $K_1[x]$. Call this factor $q_2$.
Let $K_2 = K_1[r_2] / (q_2(r_2))$.
choose a monic irreducible factor of $p$ of degree $> 1$ in $K_2[x]$, etc.

So we have a splitting field $K_n$, explicitly constructed as a quotient of $K_0[r_1, \ldots r_n]$. Let $I$ be the kernel of the obvious map from $K_0[r_1, ... r_n]$ to $K_n$. The algorithm above also gives us a Gröbner basis for $I$: for each of the polynomials $q_i$, with $2 \leq i \leq n$ let $q'_i$ be a lift of $q_i$ to a monic polynomial with coefficients in the polynomial ring $K_0[r_1, ... r_{i - 1}]$. Then it is easy to see that $B:=\{q_1(r_1), q'_2(r_2), ... q'_n(r_n)\}$ is a Gröbner basis for $I$ with the lexicographic monomial ordering with $r_n > r_{n-1} > ... > r_1$.
In general, if we have a ring $R$ with an ideal $J$, an automorphism $f: R \rightarrow R$ will induce an automorphism of $R/J$ iff $J$ is $f$-invariant, i.e. $f(x) \in J$ whenever $x \in J$. In particular, if $\sigma$ is a permutation of $\{ r_1 \ldots r_n \}$, and $f_\sigma$ is the corresponding automorphism of $K_0[r_1, ... r_n]$, we have that $f_\sigma$ induces an automorphism of $K_n$ iff $I$ is $f_\sigma$-invariant, or equivalently, $f_\sigma(b) \in I$ for each $b \in B$. Furthermore, we can test if $f_\sigma(b) \in I$ with multivariate division, which is convenient as $B$ is already a Gröbner basis for $I$.
In summary, we can check if a permutation $\sigma$ of the roots of $p$ is in the Galois group by checking if $f_\sigma(b) \in I$ for each $b \in B$, and this can be done with multivariate division.
Comment: I believe this algorithm is the one described by Susan Landau in the early '80s (and it has pretty bad complexity).


Impact vs. Regular Sockets

Question: What is the difference between impact vs regular ratchet/breaker bar sockets?  They look similarly shaped and their corresponding tool drives seem to be of the same dimensions. Are the impact stronger?  If I have impact in one size, do I need regular for using them on manual ratchets or breaker bars?
Comment: Impact sockets are meant to be used with power tools such as air wrenches or electric wrenches. If you don't intend to use power tools, go with the cheaper regular sockets.
Comment: That moment when you realize you've just responded to a two year old question, that, for whatever reason, is listed on the home page...
Comment: If you use a non-impact socket or extension in a high-torque scenario, the extension can twist, and the socket can break or strip. It's typically not visually apparent, but it's enough to throw off torque measurement, among other things. Harder material, better transmission from the tool to the fastener.
Answer: To my knowledge the difference is down to the material used
Impact sockets look black because the surface is carbonized (aka drop-forged) in order to harden the surface. The surface-hardening enables impact sockets to absorb sudden torque changes (aka "impact") better.
With high enough impact, a regular socket may warp out of shape because the steel used there is softer.
Cost aside, I cannot think of any drawbacks for using an impact socket with a regular ratchet or breaker bar, just that it is a bit overkill (similar to using a space-grade ballpoint pen to jot down notes on Earth - the ability to roll out ink without relying on gravity is wasted).
Comment: Only downside is impact sockets are more expensive, but not that much. I always buy the impact socket, so I I ever buy power tools, I don't have to buy impact sockets again.
Comment: Some sockets may be drop-forged (where heated metal is pressed into a die to form a shape) but the surface finish is likely a chemical-treatment process called conversion coating using either Black Oxide or Zinc Phosphate. They are usually performed to increase corrosion resistance.
Comment: They seem to be stiffer.  I had an oddball size bolt get stuck recently so I went ahead and tried my regular socket on my impact.  Gloves, goggles, etc just in case I shattered the socket.  Bolt wouldn't budge.  Walked down to the store, plunked down $20 for the right impact socket, walked back, zipped it right off of there.  Did some experiments and it seems the "regular" sockets flex and absorb some of the impact, lessening the effectiveness, whereas the impact sockets are stiff and transmit the pulses better.
Comment: @rana - yes, I really should mention that in the answer. But then again, you don't get space-grade ballpoint pens for peanuts :)
Comment: @DavidWinslow : You could be right, there are so many manufacturing processes out there it makes my head spin. Carburization is where the part is packed in a bed of carbon powder and baked at high temps, which gives the component a black appearance.
Comment: Now *that* is useful information. It would be great if we could substantiate it.
Comment: Here is a useful post (tengtools) that adds something to this. It specifies they use chrome-molybdenum for impact sockets, which is actually softer than chrome vanadium. However, the hardened chrome-molybdenum is harder than chrome vanadium. It seems impact sockets are softer on the inside, but with a harder surface. https://tengtoolsusa.com/blogs/news/whats-the-difference-between-impact-sockets-and-regular-sockets https://www.makeitfrom.com/material-properties/Normalized-6150-Chromium-Vanadium-Steel https://www.theworldmaterial.com/sae-aisi-4130-chromoly-steel-alloy-material/
Answer: Impact sockets are made with a softer steel that can handle impacts better. They are thicker because the steel is in fact softer and easier to bend (but not necessarily break). The reason softer steel can take impacts better is that as you impact it, the entire piece of metal compresses a tiny bit, dispersing the energy of the impact throughout the entire socket.
Chrome sockets are made from a harder steel that is also stronger, but it is more brittle and cannot take impacts well. When you impact harder steel, the energy from the impact doesn't disperse as well, and you end up with all the force of the impact being absorbed by a very small portion of the socket (very likely just the surface of it). This creates more stress even though the total force is the same, and causes a crack to form. Once the crack starts, it propagates and the socket can shatter.
Remember, stress is equal to force divided by cross-sectional area. It describes how much force a certain amount of a material is subjected to. Softer metals allow the force to be shared by the entire piece of metal more easily. More brittle metals can withstand more force if you load them up slowly, but when you impact them they can shatter.
It's also worth mentioning that impact sockets wear out faster than chrome sockets, especially if you use them with a normal ratchet. Because the metal is softer, it wears away and deforms a very tiny bit when you use it, and this adds up over the years. Chrome sockets are still worth keeping around--they will last you a lot longer if you use them properly.
Comment: This post from Snap-On seems seems to suggest that this is the correct answer - the impact sockets are actually softer. https://www.facebook.com/notes/snap-on-tools/snap-on-technical-reference-impact-vs-chrome-sockets/251237528642
Comment: And also answers the second part of the original question: Is it okay to use impact sockets with a regular socket wrench? The answer seems to be: Not really; regular sockets have thinner walls and will fit in tighter spaces, and also are better for high-torque (breaker bar) uses.
Answer: Something which has not been mentioned in the other two posts about impact sockets is the mass. While the material used for impact sockets is more robust and will stand up to a lot more abuse, the real reason there is more material in the socket is for mass. The impact gun throws the mass of the socket ahead for a brief second. The more mass the socket has, the more of an impact it will make against the fastener. This has to do with physics and Newton's second law of motion:

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

In other words: More mass = Greater impact
This bears out in the following impact socket, which is used for taking the harmonic balancer bolt out of the Honda engines:

You'll notice the wall design is about 3x the thickness of most impact sockets. This isn't because it needs to be stronger, but because of the added mass involved in the overall construction. Trying to use a regular impact on the bolt can work, but not all the time. Using this socket on them works every time. Without something like this, you are relegated to using a breaker bar with a long cheater pipe, then blocking the engine so it won't move. If only one person is involved, this is quite a chore. It's all due to the mass of the socket, not because it needs to be stronger or some other reason.
Answer: In addition, (from the product description):
Heavy-duty Socket Construction:

...drive impact sockets that feature a rugged, heavy-duty chrome vanadium steel construction with a corrosion-resistant black electroplate finish. These six-point, beveled-nose sockets lock onto drive tang for secure use. And they meet or exceed American National Standards Institute (ANSI) specifications.

Flank Drive Socket Design:

...impact sockets have a flank drive design that maximizes torque while eliminating damage to fastener. A basic socket relies almost entirely on contact with the corners of a fastener. Under high stress, the socket can begin to slip on the fastener and quickly round off its corners. Instead of contacting corners, which have little surface area, flank drive grips the flat sides of fastener, which have a much broader surface area. Large amounts of torque can be safely delivered to the fastener without risk of corner round off. The flank drive design also reduces the stresses on the socket itself for a longer tool life.
Answer: Yes this is in fact the correct answer. There are many people unaware of this. Impact sockets are thicker, heavier (for both Mass and resistance to deformation and primarily for safety). In addition, they also save the anvil (Square Drive) on your impact wrenches. Regular sockets will rapidly wear out the anvil and could even break it off completely. Though they do tend to wear out faster under impact use, it's unlikely you would wear them out if using only with hand tools, the real issue is that they are so thick, that they often don't fit or are too bulky in many tight places. Though they are softer, they are still much harder than even grade 9 Bolts, it's all about Safety
Comment: Welcome to Motor Vehicle Maintenance & Repair! Which is the correct answer? Realize what you've written is more of a comment than an answer. Stack Exchange is a Question & Answer site where comments should be clarifying in nature and not put into answers.

Impact vs. Regular Sockets


What's the best fittest length for questions?

Question: The width of the question box is fixed. But what's the best fitting length? Long questions make people scroll up and down. I want to try to shirk this possible inconvenience in my questions. How long can the question box be before scrolling happen?
Comment: Wouldn't that be device-dependent?
Comment: I would recommend staying between one line and two thousand lines. Questions with fewer than two words are likely to be closed as "unclear what you're asking", while questions over a million lines long are likely to be closed as "too broad".
Comment: @dfeuer There's a built-in length limit of either 30000 or 40000 characters (meta.SO gives contradictory information), so it's not going to get to 2000 lines (unless they lines are very very short).
Comment: @PostNoBills, is that a challenge :-? Also note that some MathJax can make things big, and of course images can easily do so.
Answer: Don't worry about how your question fits the reader's screen; worry about how it fits their brain.
Very short questions (1-2 lines) are almost universally bad (I exclude "evaluate this expression" questions). They tend to generate a stream of comments: in what sense do you use term A? What is the domain of operator B?  What is the source/context of this dubious claim you find confusing?    Etc.
On the other hand, long-winded questions run the risk of readers never finding out what the question actually is. Not everyone wants to read paragraphs of prose without knowing whether the question is something they like to engage with.
My suggestion: make it as long as you want, but

clearly isolate  the actual question,

state it early on, and  separate it from additional information (definitions, motivation, partial results)

like this.
(Formatting preferences vary; there are more than one way to achieve such effects.)
Comment: I think you've nailed the most important consideration, presenting a concise setup needed to pose the actual question, the Question itself (stated in a way that makes what is required by an Answer reasonably clear), and then some good words about motivations, approaches tried, and/or difficulties encountered/overcome.


Royal palaces just outside of major cities?

Question: I've been planning a cycling holiday in London and wanted to make a short tour to the Royal palace/castle at Windsor.  That got me thinking if other European countries have similar setup of former or current royal residences just outside of major cities?
Comment: I'm voting to close as too broad. There must be hundreds of them -- probably every royal family has a palace near the capital city and many will have several. This kind of big list [doesn't work well in the Stack Exchange format](https://stackoverflow.blog/2011/01/17/real-questions-have-answers/).
Comment: Hampton Court Palace is about 15 miles out of London https://www.hrp.org.uk/hampton-court-palace/visit/getting-here/#gs.HasJsMoX There are several in Scotland, including a palace and a castle at opposite ends of the Royal Mile https://theculturetrip.com/europe/united-kingdom/scotland/articles/top-10-things-to-do-and-see-along-edinburghs-royal-mile/
Comment: There are many royal palaces: the "summer residencies" were often outside cities (but sometime they are now within city limits, like in Vienna). You may adjust the question for the historical period of interest (and so maybe just "castle" of from 1500 to 1800). Karlsruhe has a "nearly royal" palace (also a summer residency), but royal and Germany are not so compatible.
Answer: The Palace of Versailles would seem to qualify. From the Wikipedia article:

The Palace of Versailles was the principal royal residence of France from 1682, under Louis XIV, until the start of the French Revolution in 1789, under Louis XVI. It is located in the department of Yvelines, in the region of Île-de-France, about 20 kilometres (12 miles) southwest of the centre of Paris.
Answer: The Palácio da Pena in Sintra, Portugal, probably counts as being "just outside of" Lisbon. According to the linked Wikipedia article:

[...] on a clear day it can be easily seen from Lisbon and much of its metropolitan area.
Comment: Palácio Nacional de Queluz qualifies as well and belongs to Sintra .
Answer: Saint Petersburg, Russia is known for having at least two royal palaces in the middle of the city (one hosts Hermitage and the other is Engineers' Castle), as well as multiple palaces just outside the city (still within legal boundaries): Konstantin's palace, the most famous Peterhof palace, Oranienbaum palace, Ekaterina's palace, Paul's palace and Gatchina palace (the only one outside legal boundaries).
Of course there are also quite a few minor palaces situated here and there.
Answer: It's not in Europe, but Iolani Palace in Hawaii is located in downtown Honolulu at 364 South King Street, Honolulu, HI 96813. The link above describes its location as,

Iolani Palace is located in downtown Honolulu, on the corner of King Street and Richards Street. The vehicle entrance to the Palace Grounds is located off Likelike Mall, on the left of King Street between the Palace and the Hawaii State Library.


Can I use a filtering kit with sanke kegs?

Question: I just built a d-coupler kegerator, and picked up a few pony sanke kegs from a friend.  I've been looking to start filtering some of my homebrew, but all the kits I see online require soda kegs.  Is it possible to use the filter kits with a sanke keg, or is there some technical difference that would make it impossible?
Answer: Its still keg to keg filtering.  You'll need to use different fittings from keg to tubing but operationally, its the same thing.
Comment: I read somewhere that a brewer had to switch the gas and liquid fittings, have you heard anything about that?


Different Particle Filter min and max particle numbers give almost the same result

Question: I'm using amcl package in ROS to localize a mobile robot. I've changed min_particles and max_particles several times then calculated the output difference with odomotry to evaluate these parameters. The table below demonstrate results; As you see, there is no notable change in the output and if you ignore the first row of the table, output variance is small.

And this is the Particle Filter output on the map:
Answer: Once you have enough particles to resolve your position, the effect of adding more particles shrinks to zero.  You are likely seeing the best possible results that your particle filter can achieve.
It looks like the smallest adequate number of particles for your simulation is somewhere between 120 and 1200, and my guess is that if you plotted the Odom difference vs max_particles, you would see a curve that was near-vertical at max_particles = 1, decreasing past 172 at max_particles = 120and near-horizontal at 149 by the time max_particles got to 1200.
Answer: It is not completely clear what your question is, but I assume you wanted to ask: Why does the output not change with the number of particles above a certain number of particles?
By allowing amcl to use more samples, you decrease the errors (or inaccuracies) that are caused by the fact that the particle filter approximates your probability distributions using Monte Carlo sampling. Above a certain number of samples, these errors from Monte Carlo approximation are so small that they are negligible compared to other sourceof uncertainty, e.g. measurement, system, or odometry uncertainty.
Thousands of particles are in my experience many more than you need for local localization in 2D (when the robot has a rough estimate of where it is already). You will likely only need so many particles for global localization, i.e. when the robot does not know anything (for example during initialization).


Why does Bitcoin store all transaction inputs and outputs, instead of just an "account/balance" ledger?

Question: From what I can tell, the Ethereum blockchain just stores accounts and balances - why did the original Bitcoin developers choose the method of storing all transactions for validation instead of just account balances? It seems like that would reduce blockchain size on disk quite a bit...
Comment: possible duplicate of [Can Bitcoin-Qt be configured to trim the blockchain?](http://bitcoin.stackexchange.com/questions/20000/can-bitcoin-qt-be-configured-to-trim-the-blockchain)
Comment: @NateEldredge I'm not asking about blockchain trimming, I'm asking about the original decision to implement this type of database altogether
Comment: This is an excellent question and something I have been wondering myself. Banks don't store the serial numbers of the notes when they transfer money from one account to another - in fact no notes are transferred. So why does Bitcoin store data to this level of detail? It really seems unnecessary and a perf hit to maintain the database of UTXOs
Answer: In order to be sure that an address balance is correct, you need to check that all the transactions on that address are valid.  So in order to generate a list of addresses and balances that you trust, you must first download and verify the entire block chain.
Actually, the way Bitcoin works, what you actually need is a list of unspent transaction outputs (UTXOs).  When you create a new transaction to spend coins, you don't just debit an address; you have to reference one or more specific outputs from previous transactions that you are spending.  Those previous outputs then become unusable, so that you can't spend them again.
Bitcoin Core does actually generate an indexed database of all UTXOs, and refers to it when checking transactions for validity (since this is much faster than searching back through the block chain directly).  This is the closest analogy to the "ledger" you proposed.
Once you've done this, you could delete the block chain itself and just keep the UTXO database; that is basically what the <code>-prune</code> option does (see How can I run bitcoind in pruning mode?).  However, remember that Bitcoin is a peer-to-peer system.  So you keep the block chain so that new users can download it from you.
Comment: Ah that's what I was overlooking: clients that haven't been running since the genesis block need proof that each account balance is accurate
Comment: The selected answer says 'In order to be sure that an address balance is correct, you need to check that all the transactions on that address are valid.'
But why? Why can't the address balance simply be decided by what the majority of the distributed ledgers show?
Comment: @sohrabsaran The ledger (blockchain) doesn't show address balances. Additionally, there is only one blockchain. There is no majority nor is anything done by majority or "vote".
Comment: This answer explains *how* bitcoin implemented an input/output system but not *why* it did so.
Answer: Exactly the same question was asked to a Bitcoin developer (Peter Todd) during the Bitcoin 2013 Conference.
You can watch his answer here
For those who are too lazy to watch the video the short answer is that they are doing it for security reasons.
Comment: Video can't be skimmed for important bits like text can. So not wanting to watch video isn't laziness; it's disliking the delivery medium.
Comment: Humor?!? What's that! :)
Comment: a bit of humor never hurts ;)
Answer: A nice article from corda developer, which explain why corda give up simple "account/balance" ledger and use UTXO-like ledger.
https://www.corda.net/2016/12/09/rationale-tradeoffs-adopting-utxo-style-model/
The UTXO model has these advantages:

Immutable ledger entries gives the usual advantages that a more functional approach brings: it's easy to do analysis on a static snapshot of the data and reason about the contents, even as it's changing.
Because there are no accounts it's very easy to apply transactions in parallel, even for high traffic legal entities, assuming sufficiently granular entries.
Transaction ordering becomes trivial: it is impossible to mis-order transactions due to the reliance on hash functions to identify previous states. There is no need for sequence numbers or other things that are hard to provide in a fully distributed system.
Conflict resolution boils down to the double spending problem, which places extremely minimal demands on consensus algorithms (as the variable you're trying to reach consensus on is a set of booleans).
Smart contracts are simply boolean functions and do not directly mutate state themselves. There are thus no problems with state corruption due to things like unexpected re-entrancy, as was the case in The DAO attack witnessed by Ethereum earlier in the year.
Answer: In short, the naive "account" approach is totally insecure. Fixing the insecurity without using a TXO model it seems people end up creating something which is more complex, less parallizable, and less flexible than the txout model.
For example, how do you prevent someone from just resending a transaction to duplicate a payment?  The naive fix of checking each new transaction against every tx in history has horrible performance and scalablity and isn't a realistic option.  Using a sequence number kills concurrency (e.g. if you make two transactions and someone hears the later one first, it needs to block the first; as well as concurrency in validation) and has the overhead of tracking sequence numbers.
Moreover, systems like Bitcoin were designed to use single use addresses for both privacy and efficient metadata-linking, like how do you know which invoice was paid?-- by seeing which of your addresses was paid.  If you don't reuse addresses any potential benefit of the account model goes away and all you get are the costs.
Comment: you ask: "For example, how do you prevent someone from just resending a transaction to duplicate a payment?", and go on to propose a sequence counter mechanism. Let's say that the counters of both the sender and the receiver are included in the digitally signed transaction packet broadcast to the network. Can you please elaborate on the concurrency concern? Surely each node can have some amount of memory where it can hold some transaction packets for some amount of time until the previous transaction packets arrive. This does not look too difficult to design and implement? If you
Comment: A counter prevents replay but if the system also tracks only the most recent counter it also kills concurrency: You can't transact again until your prior transaction is confirmed or otherwise it looks like a rollback.  Using a counter also means forever tracking a counter for each account, including accounts that are now empty. This makes the size of the working set unbounded even if spends of 0 are not allowed.
Comment: If we have one counter per account and average of 5 transactions per account per day, then the concurrency concern is about delay or loss of previous transaction happening for some of several thousands of nodes. How in bitcoin/blockchain are the blocks created and propagated among several thousands of nodes? Surely the same problems and solutions apply? And why to track (check) counters of any accounts other than the ones associated with the transacction packets? Counter storage is less of an issue than storing all transactions.
Comment: sohansaran Concurrency in this case means that a new transaction can't be created until a prior one is irreversible without risk of blocking the prior one, for example in a reorg.


How can I keep Tailoring?

Question: In RimWorld, I want to make "money" by tailoring, but I always need to click manually to someone do it. Can I priorize it?
Answer: Oh I figured out. I just need to priorize "Crafting".
Answer: You can also set the bill to infinite, so they will constantly churn out clothing items.
For others reading the question: to prioritize, on the Overview screen, check 'Manual priorities' then lower the priority number of crafting for the colonist who you want to craft.
Comment: Lower (as in, 1) or higher (as in, 4)? It amazes me that firefighting is 4 -I'd think firefighting takes priority over everything else, so 4 must be "highest priority"?
Comment: @Konerak 1 is the highest priority, 4 is the lowest. If multiple tasks have the same priority, the game prioritises them based on their default order left-right. In the picture, because everything is 4, firefighting is the highest priority. If cooking was changed to 3 on some colonists, they would cook before everything else.

How can I keep Tailoring?


Using Zonal Statistics Tool on raster

Question: I am working on a one-band raster with pixel values from 1 to 7, each representing a land-use class. I also have a grid of polygons and what I need is to obtain the percentage of each class in each cel of the grid.
I already used the Zonal Statistics tool and with rasters representing only one variable each it adds three columns to the attribute table of the grid: count of values, sum and average. If I do the same with the land-use raster, I only obtain the same count, sum and average values but only for the overall pixels with no distinction for the classes.
Answer: I don't know about QGIS, but in ArcMap you could use Extract Values To Table (Geostatistical Analyst)
You simply give the grid .shp and land-use class raster and the results is a table with unique values within each cell. All you have to do is to calculate the counts and percentages, preferably in R or some other statistical software (or by hand if you don't have lots of data).
I tested this with 250 x 250 m grid with Finnish National Corine data (25 m resolution) in a 7,5 x 5,75 km area. That gives a whopping 69000 observations, so if you're working on big data or at finer resolution some other solution might be better than this. Each of my grid cell has 100 land use class pixels, here is an example:

Using Zonal Statistics Tool on raster


Multi class classification always have better result than one class classification?

Question: Currently I'm using svm to classify the test samples to two different classes (True and False). When I use multi class classification, I have both true and false samples in my training set, the accuracy is always above 90%, but if I use one class classification (only true samples in the training set), the accuracy is very low (0%). In one class classification, I use radial basic function, I also tried setting different value for nu, but it didn't work.
I'm using libsvm library for java. I also scaled data before training.
Then, Did I misunderstand something about one class classification with svm ?
Thank you very much.
Answer: You should use two-class SVM instead of one-class. One-class classification is usually used to estimating the support of the high-dimensional distribution of the data. It can be used to estimate a decision boundary between two classes (usually one class vs. rest). @cbeleites gives more details about the different situations for classifying two classes.
You may want to refer to part 2 in the documentation (pdf) of LibSVM for a quick understanding of the difference in the formulation.
Comment: Support of a distribution is the set on which the pdf or pmf is non-zero.
Comment: While you explain a bit what one-class classification does and that it may not be what the OP expected, you don't explain *why* you think that binary classification is more appropriate for this problem.  I don't see information in the question that would allow to decide whether unary or binary is more appropriate. Thus, for the moment (until you explain how we can conclude from the given info that binary is appropriate) -1 as the advise is unfounded.
Comment: You made a good point. I drew the conclusion based on the fact that multi-class SVM(two-class in fact) has a relatively high accuracy while one-class SVM fails. But you are right, there is not enough evidence to make the conclusion that two-class is more appropriate. In fact, I wonder whether the OP implemented one-class SVM correctly, as the accuracy shouldn't be as low as 0%.
Comment: I dont understand the term "the support of the high-dimensional distribution of the data", can you please explain it to me ?
Comment: compare to the accuracy from multi class classification, the accuracy of one class classification is lower.. Depending on the data, in the best case, multi class classification can reach up to 98% , while one class classification stays at around 40%, in the worst case, 60% for multi class classification while around 1% for one class classification..
Answer: In general, one-class classification tackles a different type of classification problems from binary or multiclass classification.
Which is more appropriate will depend on your problem. One-class classification can deal with a type of classification task that is ill-defined in a binary sense, typically in vs. out situations where the "out" class may be everything.
As an example, consider medical diagnostics:

Distinguishing patients with a particular disease D from normal ("healthy") patients is usually a binary classification problem: both D and "healthy" are reasonably well-defined classes.
On contrast, distinguishing patients with disease D form patients who do not have disease D is an ill-defined problem from a binary classification point of view: while disease D may be reasonably well defined, "not D" can be anything. From healthy patients over all other possible diseases. This would be a situation where it may be good to consider a one-class classifier.
If however you can be reasonably sure that the measurement data / independent variates / features you use for classification will be reasonably similar for evereyone who does not have disease D, again a binary set-up is more appropriate.
Differential diagnostis that distinguishes between a given set of diseases is a typical multiclass problem.

@Yuanning already explained why the one-class classification isn't what you probably expected.
Comment: but as you said in your second point, in my case, one class classification can be also applied to my case!? Since true will be patient with disease D, false will be not D ... The fact is that I don't have good false samples (not trustable), thus I only want to focus on true samples only.


What's the point of cloasing or putting a question on hold

Question: Shouldn't a question only be put on hold or be closed after a certain amount of downvotes, not a gorup of people deciding to close the question?
Answer: The short answer is simply that the way you describe is not currently how the system is set up. A handful of people with a certain amount of standing (reputation), or elected moderators, are given the right to put questions on hold as a way to promote quality content.
See also:
https://philosophy.stackexchange.com/help/closed-questions
Comment: @user8669 I'm not sure what you are getting at; **the privilege to cast close votes can be obtained by an unlimited number of community members** — you just need to earn 500 reputation first, which is really not hard at all. Currently, that's 119 users on this site, but only a small "handful" are still active at any real level.
Comment: @PaulRoss I don't understand your objection; the ***ONLY*** reason we put questions on hold is because of quality control. The question is either a duplicate of an existing question, off-topic, unclear, too broad, or "primarily opinion-based". I actually had also written what you wrote your answer in mine as well (to prevent premature answers) but I removed it because that's really only a secondary reason — we would never put a question on hold merely because of that. The primary reason is that as formed the question is in some way not a good fit for the site.
Comment: @stoicfury, the problem is the loaded nature of "quality".  As I mentioned in my answer, asking particularly clear and focused questions is part of philosophical training.  By closing questions purely on the grounds controlling quality *of questions*, you lock out people who haven't received this training from participating.  Now, if you want to insist on Philosophy SE as a kind of Graduate School, where people who are already familiar with most of the tools of the trade are the ones asking questions, that's fine, but I don't think that's realistic on such a public forum as this.
Comment: Your "Graduate School" example is a bit exaggerated but it is in fact categorically true: Our standards do indeed require some initial "training" of sorts, except it's not really training in philosophy so much as training in how to (a) write lucid questions which are (b) on-topic and (c) sufficiently narrowed so as to be reasonably answerable. Only (b) requires any actual understanding of philosophy, and only a basic one at that. (a)+(c) are what people more often have difficulty with here, but there's little we can do but help on a per case basis, I think.
Comment: @stoicfury if questions can be put on hold or closed on a quality basis, there must be a rule that after editing (either by the author or anybody else) to a sufficient extent (or else deletion by the author),mother question must be reopened.mImhave had terrible experiences where my question was put on hold, I tried to improve and reword it, but no one paid attention to my goodwill efforts to 'fix' my question. As for the 'too broad' classification: philosophy is broad naturally. It is not math or science where there are specific questions and specific answers.
Comment: The creators of this website desire a certain level of factuality to the content they host; they want questions and factual answers, not questions and unsourced rants. We do what we can here to respect these goals while also allowing a great deal of "wiggle room" as long as the question is (a) clear and (b) sufficiently focused so that the answers — as unsourced and opinionated as they are — remain generally all in line with one another to a certain extent. The question example about [downloading music](http://philosophy.stackexchange.com/q/1597/514) is my own in fact and a good example. (2/2)
Comment: I think this is misleading as an answer as it stands, since it implies that what lacks quality is the question that is being put on hold.
Comment: @stoicfury, what I am asking is why is this process (quality control) not undertaken by the entire community on the website? Why are the 'handful of people' (even with their reputation) able to make decisions that everyone should be able to partake in?
Comment: @stoicfury I think here's an example case where closure pending discussion would have been an appropriate response, but *nobody* (as of the time of this comment) has yet voted to close it and it's already attracted a couple of very cheap answers: http://philosophy.stackexchange.com/questions/15181/are-there-counterarguments-to-chaos-theory  . The user clearly is looking for philosophical discussions of Chaos theory, but the best contribution so far has been the comment linking to a relevant SEP article and prompting further discussion.
Comment: Ping the people who closed it or a mod if you believe your edits make your post eligible for reopening ("@stoicfury - check my edits! :)"). Note that this is automatically done for everyone when you add a comment on a post they've already commented on, but sometimes things do slip through the cracks (hence why the OP needs be proactive sometimes). With regard to your last comment, this site was originally designed for academic philosophy which *does* have very specific questions and answers. It's not really for *doing* philosophy, although we do allow it with sufficient focus and development.
Comment: But isn't asking questions about philosophy (unless it's the nitty-gritty who said what in which year) the same as doing philosophy?
Comment: @user8669 - That's an interesting philosophical proposition right there in itself, but generally we would say that they are very different concepts. For example, we make a distinction between people asking questions like "What did Hegel mean when he wrote X?" or "What would an Act Utilitarian do in Y scenario?" and questions like, "What is the meaning of life?" / "Do people have the right to complain?" / "Is it immoral to illegally download music?". The distinction being that you can look up the answers in a book on one hand vs. what usually ends up being a bunch of rambling opinions. (1/2)
Comment: The question about morality of downloading music seems to me to be an opinion question. I am no sure how it can be considered factual.
Comment: If you read the question body you'll see it's actually much narrower than that in that it attempts to follow a series of conclusions to the furthest point possible and essentially asks whether the conclusion is wrong. "Is it immoral to negatively affect someone's potential wealth?" I suggest that it is "ridiculous to think so", but invite others to contest my logical deduction. Again, the point is that it's not "factuality" *per se* but a sufficiently narrowed focus that matters. The community decides what is OK and what is not, and the votes are the indicator. (1/2)
Comment: The same goes for questions like [this](http://philosophy.stackexchange.com/questions/10823/am-i-morally-obligated-to-pursue-a-career-in-medicine), [this](http://philosophy.stackexchange.com/questions/596/what-would-it-take-in-a-book-to-convince-a-rational-person-that-it-had-been-writ), [this](http://philosophy.stackexchange.com/questions/537/what-should-philosophers-know-about-math-and-natural-sciences), and many others... (2/2)
Answer: A big reason to put questions on hold early is to stop people submitting premature answers.  Questions asked without much experience of philosophical argumentation, particularly of the terminology, concepts or logical technologies that have tended to be used in philosophy, sometimes need a little support to help work them into a form that invites strong answers.  Otherwise, people might be tempted (and I know I particularly fall prey to this temptation myself) to submit answers to the questions in the form that they've been asked, rather than in response to what it is that the asker might really like to know.
Questions are put on hold whenever it seems like there is some uncertainty as to exactly what the question is asking, so that discussion can take place to help resolve that uncertainty in some way before others try to capitalize on it with cheap and smug answers.
Comment: I really do want to stress that we do not put questions on hold because we are bent on making people suffer on the internet. We just want to maintain certain levels of quality on the site using standards the community has been using successfully for a long time now. In time the community's stance on certain things may change over time, but that's up to the community. I personally do try to edit questions as best I can before I put them on hold, but some are just so unclear they need clarification from the author. But the network will never force people to edit first, and we can't change that.
Comment: Paul, thank you for your answer. The problem is that even when I try multiple times to edit and improve my question (after it was put on hold), I do not get a response and certainly the question does not get reopened. I suggest making a rule that a question put on hold must be edited by either the author or the people who put it on hold (or else deleted-- but only by the author). If any party is no satisfied with the edit(s), the process can be repeated as many times as necessary.
Comment: @user8669, I think one of the reasons for this may simply be a lack of users of the site who would have enough expertise in particular fields of philosophical inquiry to help supervise you through working up your question.  The site is run by volunteers and a community, so there's not much incentive for professional academics to contribute when they have their own students to help train!  That's unfortunately just a problem with running a Q&A site on fields as deep in literature as the many philosophical topics.
Comment: @user8669 I know for my part I tend to keep a close eye on questions that have been explicitly tagged in fields I have some academic training in, so maybe good use of tagging might be a way to encourage people to help you out with your question?  Have a look at what kinds of tags people are using in the tag lists, what kinds of questions are similar to yours, and see if you can slot your query in with others like it.  And when in doubt, just add another tag; the worst that will happen is a mod will remove it!
Comment: Paul, if there is a deficit of professionals in fields pertaining to the questions asked, those questions should not be closed in the first place. Only a professional can deem a question 'bad' or wrongly (unclearly) phrased. Those 'professionals' who close questions should be willing to edit and improve them!
Comment: Questions have to be clear enough to be understood by users of the site. If you ask an esoteric question that is technically well-formed but no one else in the world understands it, functionally that is the same as asking a poorly formed question which will be closed. In practice however, this never happens; we have a lot of bright people here, and if 5 people close vote your question then it's probably a pretty good indicator that there's something wrong with it and not simply a failure of their intellects. If you think a question should be reopened after edits, post it in META or ping a mod.


What is the formal statement of the dining philosopher's problem?

Question: I've read about it in a few places and I'm not sure I get it.
Are the philosopher's allowed to act simultaneously?
Do they each take 1 action simultaneously, then go on to their next action?
Comment: It's up to you (or whoever tasked you with the problem) to define what actions the philosophers have at their disposal. The problem is an educational device. For a bit of history, check EW Dijkstra's papers on the topic. You can [search his archive](http://ewd.cs.utexas.edu.master.com/texis/master/search/?q=dining+philosophers&xsubmit=Search&s=SS).
Answer: In most models of concurrency, each participant performs one elementary action at a time. This applies both to philosophers and to forks. So if two philosophers try to grab the same fork around the same time, one of them will make the attempt first.
Concurrency models usually do not have a global time, so there is no concept of actions happening "at the same time" if they don't involve the same object. Each participants sees events according to its own notion of time. If an action happens which doesn't involve a particular participant, that participant only learns about it later when it receives some message informing it that the action has taken place.
Think of the participants as nodes in a network (which they often are). If two actions happen on different nodes, it doesn't matter whether they're "exactly" simultaneous. And physically speaking, they wouldn't be exactly simultaneous: without perfectly synchronized clocks, there's always some slight measurement error or reaction delay that means that you can't distinguish perfectly simultaneous actions from actions that happened within an extremely small time frame.
Each philospher decides to pick up and set down forks at their own pace. One philosopher may pick up a fork, eat and set it down before his neighbor has lifted a finger. Or they may race for the same fork, but only one of them will manage to grab it. Meanwhile the other philosophers are doing whatever they please.
Having one timeline per participant, rather than a global timeline, both simplifies the model and makes it closer to the reality of most concurrent systems. The model is simpler because there's never any reason to treat actions as simultaneous, and never any reason to care about the exact order of actions happening in different places. It's closer to the reality of concurrent processes and distributed systems because each thread or each network node does have its own perception of when actions take place.
An exception is the modeling of circuits where all actions happen on a clock cycle. This is one of the fundamental ways in which parallelism differs from concurrency. In a circuit, it often does make a difference that two actions happen at different parts of the system on the same clock cycle (e.g. two inputs change simultaneously), rather than on distinct clock cycles.
Answer: Having the philosophers act simultaneously (like if two of them try to pick up the same fork at the same time) would potentially make the d.p.p. even worse.
But with the "bad" algorithm presented on Wikipedia, if all philosophers pick up the fork on their left, at times $t_1,\dots,t_5$, then we have deadlock no matter what the times $t_i$ are.