Why did the banks sell credit default swaps to Michael Burry in The Big Short?

Question: In The Big Short there's a scene where Michael Burry shorts the housing market by going to different banks and buying insurance from them.
After he leaves, we see the bank employees making fun of him for making a terrible deal.
Yet in the end it is revealed, the banks knew all along the crash was going to happen but also knew the taxpayer was going to bail them out, which is why they basically bribed the ratings agencies to fake the ratings of the mortgage bonds.
So why did they sell the insurance to Micheal Burry, when they knew he was going to profit heavily of them?
Just to keep the illusion going?
Comment: Banks are big organizations with dozens of departments and thousands of employees, and not everyone knows what is going on. The banks didn't necessarily always know the market would crash. They figured it out eventually. And not all the banks figured it out either
Answer: [Skip to end for short version]
The movie dumbed it down and made the banks look hapless.   It was almost like the banks wrote the script.   Only boy genius could figure out that the housing market was going to crash.
So in the movie the scenes you are referring to happened on film because:

Going over the exact reasoning would be even harder to understand than the other stuff they already brought up.

The big banks would go nuts and possibly sue the studio.

I worked in quant and direct feeds during this time in the market, doing a lot of work for big banks (I was the guy that got them data faster so they could game the system pre-regulations).   This plays out real real simple.
You have guys who are handing out loans and giving criteria for portfolios of loans being handed out.   They allowed lenders to bypass PMI and basically let people buy houses with no money down.
Example:  Standard is 20% down on a house.   If you don't have 20% of the house you pay PMI which is a B*TCH but protects banks.   Here is where it gets shady.   There was this huge cross-section of people that didn't have the money to pay for their down payment + mortgage + PMI - so these people where denied or simply chose not to get loans.
But but but the big banks whispered to the direct lenders...   we want more loans no matter what.   So if someone buys a 200k house and they don't have 40k down let's figure something out.   We make them put maybe 10k down give them a 30k loan as a second mortgage (on a house they don't have yet) and give them the home loan.  Yep 5% with no PMI (PMI on a 200k loan right around $200 per month).
Pretty shady right?   That was step 1.   Step 2 is let's get that 2nd loan off the books and charge them for another new loan.   So let's tell all of our lenders to target potential houses that they could get (maybe fake) appraisals done at a much higher estimate.   Guy comes out and says the house is now worth 240k...  Well now your equity stake is 20% and we will give you a loan for the 190k.   Boom new loan on books.
The big banks new what they were doing.   They had systems with all of these loans categorized and segmented based on loan type, customer type, and risk.   So when the default rate of 3rd year borrowers went from 1.057% to 2.7% their algorithms knew what to expect down the road.
The fact is all of the jobs at these banks are bonus-able on what you did this year.   These guys get a $5m bonus for giving out 10 billion in loans... They could care less what crashes in 3 years or forecasts.   So all of the managers on this side of the company knows what's coming.   But if they try to save the ship or reduce risks, they are mitigating their salary.   So they basically hid it until the last second.   This is the main point the movie should be ashamed for not portraying accurately.  For such a good movie it is pathetic that they made the banks look shocked.
Why didn't the guys selling the short know?   They would have no clue and would never be allowed to see the data (at least the accurate data) that the loan division heads have.   So the #1 evil is the banks manipulating the market to sell loans.   But in a very close 2nd place on the evil list is the idea of handing out huge bonus for short-term performance in the banking industry.   Basically you get your huge bonus no matter how much you screw the company over long-term unless you broke some law/regulation.
[To understand why they were happy to sell the short, you would need a meta movie about the loan department.   This movie would probably be just as intriguing as The Big Short and would go over the 3-4 year cover up of the loan portfolio books.]
Comment: So, keep in mind that this is a movie based on a book, and while I haven't read the original book (though I plan to at some point), you kind of have to expect it's going to be watered down. In reality that was one of my big takeaways from the film, especially with the celebrity segments explaining certain concepts: the movie was designed to entertain and inform, but had to do so in a way that dumbs things down and is explained by attractive and popular celebrities for people to pay attention.
Comment: @MattD - I thought the movie did a great job of explaining things on a basic level.   A+ actually.    I have not read the book but I would be deeply disappointed if it had the same tone of the movie.    The problem wasn't the explanations the problem was the portrayal of the large banks in the US.    They were all in on it and shady as hell.    Lehman went under because of their political ties (not enough) and the rest were given "loans".   If this had happened to small midwest banks in a micro sense half the people involved would have jail time.
Answer: Two reasons. First, banks do not generally have monolithic investment hypotheses. It is totally possible for different parts of the bank, or even different traders on the same desk, to have offsetting views. Note for example the relationship between Donald Trump and Deutschebank — he defaulted on their commercial lending division, sued them, and they declared they would never do business with him again. The personal banking division of the same bank was delighted to take his business, even to the point of lending him the money needed to pay off the division of their own bank that he had just defaulted on.
Second, banks act as intermediaries, selling exposure to one side and laying off the risk elsewhere (perhaps somewhat transformed, by being embedded in an indexed derivative or a structured note for example). In such cases, the bank is left with little or no principal risk and takes a spread.
Comment: I think this misses the point somewhat that the banks just didn't see the collapse coming until it was too late.
Answer: This is to go along with Michael Stern's answer about how different arms of a bank may act differently or seemingly independently of one another.
The dialog of the scene depicting Burry discussing the purchase of the insurance swaps would clearly indicate that, at the very least, the quants he was dealing with did not know such a crisis was on the horizon. They even seem to try and convince him his request is both highly improbable and foolish:

Michael Burry: I want to buy swaps on mortgage bonds. A credit default swap that pays off if the underlying bond fails.
Goldman Sachs Sales Rep (Lucy): You want to bet against the housing market?
Michael Burry: Yes.
Goldman Sachs Quant (Deeb): Why? Those bonds only fail if millions of Americans don't pay their mortgages. That's never happened in history. If you'll forgive me, Dr. Burry, it seems like a foolish investment.

This happens around 2005, roughly two years before the housing market would start to collapse in 2007, culminating in the bankruptcy of Lehman Brothers in September 2008 depicted at the end of the film. The quants legitimately thought what Burry was betting would happen could never happen, and were all too happy to take his money.

Goldman Sachs Sales Rep (Lucy): This is Wall Street, Dr. Burry. If you offer us free money, we ARE going to take it...

I mean to be fair, they're actually being quite reasonable here in trying to warn him against the action he's seeking to take, but if he wants to do it they can certainly make it happen and won't bat an eye. They even laugh among themselves in celebration after he leaves because they legitimately believe they're going to make a small fortune of Burry and can't believe what just happened.
Leading up to this moment, even one of Burry's biggest clients thinks he's wrong.

Michael Burry: It's only a matter of time before someone else sees this investment. We have to act now.
Lawrence Fields: And how do you know these bonds are built on subprime crap? Aren't they filled with hundreds of pages of mortgages?
Michael Burry: I read them.
Lawrence Fields: You read them? No one reads them. Only the lawyers who put them together read them.
Michael Burry: I don't think they even know what they made. The whole
housing market is propped up on these bad loans. It's a time bomb, and I want to short it.

The dialog is also notable for Burry's insistence at acting quickly to be the first to obtain these types of swaps, because he thinks someone else will see it as well and seek to capitalize on it.
As the movie shows at least two other groups learned of the problem and sought to capitalize on it.
Eventually the guys at Brownfield learn the SEC has zero regulations on mortgage-backed securities, and as the defaults rise but the CDOs and mortgage bonds remain the same or even go up in value, they surmise the banks are aware of the issue and are attempting to sell and short them before the looming crash. They attempt to alert the press, but no one of relevance will listen to them.
This is pretty much the central point of the film: the banks at first didn't seem to realize the impending doom, or at least didn't think it would be a big issue because, "Who doesn't pay their mortgage?"
But as the movie would show, mortgage lenders were also acting unscrupulously and lending to people that were massive risks because of the money they were making, and when things went sideways the banks acted fraudulently to protect themselves due to little to no regulations on the investments involved. Eventually they were bailed out, no one of consequence was arrested, and virtually no effective regulation was put in place because banks are now selling CDOs under a new name, "Bespoke Tranche Opportunity."
Comment: still seams pretty insane that Micheal Burr is the only one to just sample a few mortgages in a few CDO and figure out that the creditors behind them are very likely to default
Comment: @user2741831 That certainly is a very baffling aspect of the whole story, that a very small set of people not even working together saw what was happening and capitalized on it.
Answer: There's more than one bank. It's no more a contradiction to say that "the banks" knew it was coming and yet "the banks" were betting against it happening, than it's a contradiction to say "the soldiers" were trying to land on Normandy Beach, and "the soldiers" were trying to stop them. By the time of the events of movie, mortgages were being moved from one bank to another, in increasing complicated arrangements. Max Greenfield plays someone at the beginning of this chain: he gets people to take out mortgage loans, and the bank that makes the loan quickly off-loads it to another bank, who may then combine it with several other mortgages to create a CDO and sell it to another bank, who sells it to another bank, etc. He doesn't care whether the mortgages are good, because his employer doesn't care, and they don't care because they're just selling them to someone else.
And within one bank bank, there are different divisions that are often working at cross purposes. The character Jared Vennett is based on Greg Lippmann, who was betting against the CDOs while other divisions of his employer,  Deutsche Bank, was investing in them.
Third, this takes place over several years. The banks didn't all start out knowing it was going to come down. As time went by, more and more banks went from selling the insurance, to getting out of the business, to trying to buy insurance themselves. It was Burry buying this insurance that tipped Vennett/Lippmann off to look more closely at the CDOs, which made him realize he should bet against them, which led him to wanting to go out and sell insurance to investors, which led him to Mark Baum (based on Steve Eisman). As Vennet sells more and more insurance, more and more people, such as Charlie Geller and Jamie Shipley, start to see the cracks in the industry.
Also, the bailouts were primarily of the underlying mortgages, which were backed to some extent by federal programs such as Fannie Mae. The bailout of entities holding derivatives based on those mortgages was more sporadic.
Comment: that scene in particular, wouldn't someone outside of the financial world have found it weird that immigrants were suddendly getting insane loans that they almost certainly wouldn't be able to pay back?
Answer: I think it's a stretch to say the banks knew the crash was coming. Yes in the closing moments of that bubble they could see the market start to wobble, but most bankers, most investors, most homeowners, were oblivious to the impending doom before that pint. The bankers who laugh at him think they are making easy money because his bet is (in their opinion) a stupid one. But he was placing his bets at least a year before the cracks became visable to the market.
In the immediate aftermath the heads of the banking industry knew the government would have to bail them out, but before the collapse begin they couldn't see it coming because it was unprecedented and they were blinded by greed.
Read the book if you'd like more detail. It's one of my favourites.


Can I allow front-end users to PUBLISH articles in specific categories?

Question: Can I allow users to PUBLISH articles in certain categories without giving them the ability to publish to any category. It seems that they can create articles but then the article requires someone with PUBLISH permission to actually publish the article.
Answer: We have a feature called Access Control List (ACL), with this
you can create a user groups and assign them permissions to
access, create, edit or delete content or modify certains parts
of your site like articles, categories, modules, global configurations, etc.
For example, we have the user group "Author", in the screenshot you can see a
 category called "Blog", in the "Permissions" tab we can allow or denied actions.

Here some docs:
https://docs.joomla.org/ACL
Here a full example:
https://docs.joomla.org/J3.x:Access_Control_List_Tutorial
Best Regards!


How far apart should temporary A braces be on 18ft side walls before permanent bracing?

Question: I was wondering if anyone knew if there was a code for temporary bracing of a non-residential building before it is permanently braced with plywood? I was curious to know how far apart each "A" brace shoud be on an agricultural building in Minnesota, used to store machinery, that is 50'x80' with 18ft sidewalls?
Comment: This is really out of the realm of DIY home improvement.  If I were you, I'd be checking with local building inspector or your insurance company if this is a commercial job and you are the contractor. This would be an OSHA guideline, not a IRC code.
Comment: What is your particular involvement in the project? How far along is the project at this time?
Comment: Adequate permanent bracing for a building that size should include more than just plywood.
Answer: I would suggest that you brace as required to keep the structure straight and square. The sidewalls will be affected by how straight the lumber is in the first place and also by the process of installing the side wall sheathing. You will need bracing as required to push the shape of the framing into plumb and square and then hold it there.
Also be aware that since the integrity of the structure is not complete until the roof trusses are placed and fastened to the upper plate of the sidewalls you will need bracing in place to deal with forces of nature. As you begin to install the side wall sheathing even moderate amounts of wind can place significant pressure on the wall structures so bracing will be needed to make sure that a strong gust does not come by and flatten all your work.
Comment: What would you say would be adequate bracing? Would "A" braces every 16ft be enough? And what about once the sheathing is on and everything is square? would 16ft be enough again?
Comment: As I said in my answer... "as required". You may need bracing at differing locations to ensure that the structure stays straight, square and plumb. There is no general rule here. One thing that can be said is that a sixteen foot wall section that is 18 feet high could be extremely rigid or could be wobbly as the dickens depending how it is framed, types of materials used, lengths of lumber used. This variablity will dictate, to some degree, how much bracing is needed. On the job at the site experience will be your guide. If the framing itself incorporates intrinsic bracing that helps too.
Answer: More. Braces. Because I'll huff....
When the contractor showed up to come take over building our summer home for us (we got as far as the first floor walls), he said one word to his crew, "Braces." We had them every 10+ feet or so. They put them every 5' or so inside and outside, one to the deck and one to a post sunk in the ground, forming an 'A'. Lots of 'em, as I've learned. I wouldn't sheath anything until the trusses were up (the manufacturer of them is whom you should consult on the bracing required for a 50' span). The bracing used to plumb the trusses (the laterally run 1x4's) is not temporary, it becomes part of the structure as blocking.


Is there any opening line which is downright catastrophic?

Question: I have played 1.a4, h4, f4 in an engine and it gave me the opening line's name. I mean, how could it be considered a line as it, at least IMO, don't do anything that defines a good opening. (fight for center, develop your pieces etc.)
Comment: First, there's no law saying that only good things have names. For instance smallpox, influenza, leprosy, cancer all have been names. So why shouldn't bad openings have names? Second, Bird's opening 1.f4 is not really bad. It does fight for the center, by controlling e5.
Comment: People with various degrees of skill and knowledge of theory have been trying ideas for a long time. Sometimes, these ideas get named.  "The Grob" (1. g4), "The Spike" (1.g4 d5 2. g5),  "The Polish" (1. b4), "Wares" (1. a4)  Most of these don't stand up to GM scrutiny which is why you don't see them in tournaments. However, these odd looking moves can contain surprises that catch club players off-guard and yield a point to the person playing them. Getting a win with an "unsound" opening counts as a win on the scorecard! The crazy games that come from them are probably a lot of fun, too.
Comment: What two moves did you have black play between those three moves?
Comment: @RickyDemer Maybe the OP means that he played 1.a4, 1.h4, and 1.f4, and in each case the machine gave a name to the opening?
Answer: If you mean "Is there any first move for white which is catastrophic?" then the answer is "No". There are first moves for white which look bad. Na3, Nh3 and f3 would be my candidates but they are not catastrophic.
Na3 could be followed up by moves like b3, c4, Nc2, Bb2, for example, to get a playable position. Perhaps not the best use of first move advantage but certainly not catastrophic.
The problem for black when white makes a "bad" first move is to try and steer the opening into one where the "bad" move is really a bad move in the context of that opening or at least irrelevant so that white's first move advantage has gone.
White's contrasting problem is to try and steer the opening towards one where the "bad" move becomes good. For instance, after 1.h4 if white can steer black into fianchettoing his king's bishop and castling kingside then 1.h4 could become a strong threatening move.
If by "opening line" you mean a sequence of moves then, yes, there are catastrophic lines and yes, they do often have names. The most famous is  probably Scholar's Mate:
<code>[FEN ""]
[Event "Scholar's Mate"]

1. e4 e5 2. Qh5 Nc6 3. Bc4 Nf6?? 4. Qxf7#
</code>
The shortest possible mate and so the most catastrophic is Fool's Mate:
<code>[FEN ""]
[Event "Fool's Mate"]

1. f3 e5 2. g4?? Qh4#
</code>
Comment: I liked the bit about h4 being a strong move, when bishop is fianchettoed. it gives us a strong queenside attack(if played well) . But also, the thing I was asking for was that aren't the openings downright catastrophic if played against best play (assuming white plays best too)?
Answer: I would say the value of an opening is conditional on your opponent:

You against a computer with almost perfect play: all openings are bad. You'll lose anyway (unless you are a super GM), but some openings are worse than others.
You with the help of a computer against another computer or player with a computer: some openings lines are bad, some are ok, and some are good. A computer will not forgive your choosing an opening line that leaves you in an inferior position. With most openings you'll end up in draw. And if you want to win you have to choose some anti-computer opening.
You against a human player: to estimate the value of an opening line against a human player you have to evaluate which is their opening repertoire and their playing level relative to yours and which is the type of competition. Against a player with a similar rating, you might try to surprise them with an uncommon opening (that you have studied well) to get them out of book. This strategy can be more useful in rapid and blitz games, since it is more probable the opponent will make an error you can use in your advantage. For example, Carlsen played 1.a4 against Radjabov in the World Blitz Final in 2012 (and won). But with a player with much more experience than you, it might not work anyway.
Answer: My favorite catastrophe is probably the Blackburne Shilling Gambit, probably because I fell for it once :-S.
<code>[Title "Blackburne Shilling Gambit"]
[fen ""]

1.e4 e5
2.Nf3 Nc6
3.Bc4 Nd4?!
4.Nxe5 Qg5
5.Nxf7? Qxg2 6.Rf1 Qxe4+ 7.Be2 Nf3#
</code>
Gotta be good for White, right? Grabbing the f7 pawn AND forking the black queen and rook! While White's rook is easily saved from the Qxg2 threat via Rf1. Heh.


Deep Learning model for classifying skin diseases

Question: I have planned to create a deep learning model that classifies skin diseases(around 5 to 7 diseases). Please suggest me a good deep learning model to go with. I am planning to integrate this model as a mobile application. It goes like this. The user uploads a skin disease image and the machine is going to classify it accordingly. I need a good degree of accuracy.
Answer: If you are classifying images, you should obviously use CNN for good accuracy.
The dataset you are classifying also plays a great role in determining the hyperparameters, optimizers, loss function.
So you should start with a basic CNN model that you can train with optimizers such as SGD and try tuning the hyperparameters accordingly.
If you are asking about the transfer learning models you can use RezNet or GoogLeNet
Answer: For the classification of images, use the Convolutional Neural network(CNN) Or you can opt for the Pre-trained model that was trained on a large amount of dataset Which provides good accuracy. Examples of the pre-trained models are VGG, MobileNet, Inception V3, etc.
For choosing various hyperparameters you can use the grid search approach.
Answer: There are tons and tons of architectures that you can try even in convolutional neural networks. If you have a sufficiently good amount of data, you can apply any of the ResNets (ResNet18, ResNet34, ResNet50 etc..), ResNEXTs, or any light image architecture is sufficiently good for such tasks, it gives a great balance between performance and time of execution. But if you want to achieve a really high score and have a sufficiently huge amount of data, you can refer to Efficient-Nets for your models.
Answer: You may take a look at the ISIC challenge. I used an Unet for this lesion segmentation and afterwards, I applied a ResNet to the lesion.


Screen saver settings keep defaulting back to National Geographic Photos

Question: I like to use my photo library for a screen saver (have 10,000 photos - it's nice to get to see them more often), but ever since I've downloaded Yosemite, every time the computer goes to sleep, it defaults back to the National Geographic photos (there are maybe 30 of them).  Really, really frustrating, and I can't find where to change the default settings to try and make an adjustment.  Anyone know how to change that default setting or have any other idea what to do?
Comment: Do you use Mission Control and have multiple desktops with Desktop Backgrounds?
Answer: After trying the other "fixes" and nothing worked, I went with what was previously suggested here.  Located the Nat Geo folder (HD>Library>Screen Saver>Default Collections>1-National Geographic) and removed those pictures.  This does require your Administrator Password. Then I moved the pictures I wanted into that folder. This works, but it is not a fix as the Screen Saver still defaults to that folder.
Answer: @Charley3's answer did not work for me, as I constantly update the photos I want in my screen saver. I took it one step further by setting up the mac to copy the photos from my folder to the default national geographic folder once a day on weekdays:

Open Terminal application
Type sudo crontab -e
Type your password
Type i and then paste the following: (03 7 is 7:03am, change to desired update time. 1-5 is Monday-Friday, change to desired days)
03 7 * * 1-5 cp -a <path to screensaver photos desired>/* /Library/Screen\ Savers/Default\ Collections/1-National\ Geographic/
Type [esc] :wq and hit [Enter]
Type sudo crontab -l and verify the information pasted in is correct

Now I can have the photo folder that I change the contents of daily still be set as my default screensaver folder.
Edit: In addition, I selected the 'shuffle slide order' checkbox in screen saver settings but that too shifts back to the defaults. In order to check this box regularly, I used this question and added an additional line to the crontab:
03 7 * * 1-5 /usr/bin/defaults -currentHost write com.apple.ScreenSaverPhotoChooser 'ShufflesPhotos' -bool "true"
Answer: I had this same problem. For me it was caused by a configuration profile that was overriding my screensaver preferences. (I had installed the profile while going through Apples OS X Support Essentials book)
Here are Apples instructions :
Remove a configuration profile from your Mac

Choose Apple menu > System Preferences, then click Profiles. If you
haven't installed any configuration profiles, the Profiles pane of
System Preferences isn't available.
Select a profile in the Profiles list, then click Delete (-).
Comment: This was it for me. My company had installed a profile that reset the screensaver.
Answer: It's very frustrating that apple has done nothing about this bug. If you search the forums, a lot of folks have this issue.
If you look at the apple forums there are a couple of workarounds but no fixes.
Two things work for most folks:

Find the national geographic folder, delete the pictures there and move your screen saver pictures to that folder

or

Leave the screen saver preferences always running (never close the window)

Some of the other solutions offered have mixed results:

Deleting the national geo picture folder (works for some, others get a "no pictures message")
Deleting system "plist" files (works for some, others claim the problem - returns after a while).
Disconnect your system from the internet (Not sure why but some folks claim when not connected to the internet the screen saver does not revert back).
Comment: deleting the entire national geographic folder worked for me. removing all the mac.screensaver files did not.
Comment: Do you have a radar number I can duplicate? Can you reproduce this issue on a new installation? What precise files need to be deleted if you wish to delete "system plist" files? (I am suspicious that the preferences are actually stored in a database as opposed to plist files, but let's see if we can at least nail down where the screen saver settings are stored)
Comment: @bmike I can see the current selected folder in the file `~/Library/Preferences/ByHost/com.apple.ScreenSaverPhotoChooser.438F481F-1D78-5338-B855-BBEAE4274C8B.plist`. It regularly reverts back to the NationalGeographic folder. I tried making the file read-only and will see if it works.
Comment: It turns out the plist is erased even when read-only. Also making a copy of the "good" one and copying it back doesn't seem to have any effect.
Comment: I tried replacing the NationalGeographic folder with an identically-named symlink to the Dropbox folder I want to use, but when it reverts I still just get a "No Photos" message. I'll try Sashah's method above.
Answer: This is not a fix, but a work-around. Goto preferences and in screensaver select your personal photo folder you want to use, in the upper lefthand corner select the yellow (minimizer button) the screen will zoom down to the dock thereby locking your selection open on the dock. Not a fix, but at least you can see your own photos.
This is the only thing I've found that works—picked up from a post somewhere else.


Is O(ln n) "exponentially faster" than O(n)?

Question: I improved the complexity of an alogrithm from $O(n)$ to $O(\ln(n))$. Is it legitimate to call this an "exponential speedup" in a scientific publication? Usually I think going from NP to P when I hear the phrase "exponential speedup". I'd like to avoid overselling my work.
Comment: @AndréSouzaLemos $2^{\log n}\to\log n$.
Comment: Beware of associating "exponential" with **NP**! We don't know that **NP**-complete problems require exponential time. Also, on a more subtle level, it doesn't really make sense to talk about "going from **NP** to **P**".  Complexity classes are collections of *problems*; what you've done is produce a new *algorithm* (see our [reference question](http://cs.stackexchange.com/q/13669/9550) for more).
Comment: Of course it is an exponential speedup.
Comment: Sublinear sounds fancy, I might go with it. However, I can you give a mathematical reasoning, why that cannot be considered an exponential speedup? I can process exponentially more data in the same time compared to before.
Comment: I wouldn't use "exponentially", unless an actual exponent could be directly indicated, somehow.
Comment: @DavidRicherby It's a matter of taste, but to me this is a terminological hack.
Comment: @DavidRicherby You are right of course. My use of the terms was sloppy.
Comment: @YvesDaoust, André Souza Lemos Could you comment on Ran G.'s answer, please? It pretty much sums up why I wanted to call it an exponential speedup in the first place. On what grounds would you disagree with it?
Comment: It is correct, obviously, and I always thought so. It still doesn't *feel* right, though.
Answer: How should we measure (asymptotic) speedup?
Say we wish to compare two functions, $f(n)$ and $g(n)$, and say something on their asymptotic behavior, that is, how they behave for large enough $n$'s, in the limit $n \to \infty$.
Let's start with a few examples.

Example 1:  $f(n)=2n$ and $g(n)=n$.

Here it is obvious that $f$ is "twice as slow" as $g$; This is true for any $n$ and also in the limit. This needs not be the case. For instance

Example 1.1:  $f(n)=2n$ and $g(n)=n+1000$.

Well, now, for $n<1000$, $f$ is actually faster than $g$. But still, if we take large $n$'s, we want to say that $f$ is twice as slow as $g$, or in other words, the speedup is 2.
Why 2? Because the ratio between $f$ and $g$, in the limit, is 2.
Let's take a different example to emphasize this issue.

Example 1:  $f(n)=n+10$ and $g(n)=n$.

Here, $f$ is slightly slower than $g$. What is the speedup between $f$ and $g$? By how much is $g$ faster? The answer is "by 10 clocks". But speedup is measured as a ratio - "twice" as fast means it would take (approx.) twice the time to run the slower function. Here the ratio is approaching 1
$$\lim_{n\to \infty} \frac{f(n)}{g(n)} \to 1$$
That is, the 10 clocks don't make any (multiplicative) difference. Running 10000 clocks and running 10010 clocks, is practically the same (the speedup is $<0.1\%$).
I hope the above establishes that the (asymptotic) speedup between $f$ and $g$ should be defined as
$$\lim_{n\to \infty} \frac{f(n)}{g(n)}.$$
When the speedup is not a constant, then the best way to describe the speedup is to set $g(n)=k$ and ask how $f(n)$ behaves as a function of $k$. If $f(n) \propto k^2$, then the speedup is "quadratic". If $f(n)\propto k^3$ the speedup is cubic. If $f(n)\propto 2^k$, the speedup is called exponential. Not that it is important to set $g$ as the base unit ($=k$). Otherwise, If we take $f$ as the base unit, then a quadratic speedup translates to $g(n)=\sqrt{k}$, which may be a bit confusing. Maybe its better to think at the other direction: instead of considering the speedup from $f$ to $g$, look at the slowdown from $g$ to $f$. (.. if $g$ is twice as fast as $f$, then $f$ is twice as slow as $g$)
If we agree on this, we can check the speedup between $f(n)=n$ to $g(n)=\log n$.
$$\lim_{n\to \infty} \frac{f(n)}{g(n)} = \lim_{n\to \infty}\frac{n}{\log n}$$
Let's change the limit variable, to make $g$ the base unit for the comparison: set $k=\log n$, then,
$$\lim_{n\to \infty} \frac{f(n)}{g(n)} = \lim_{k\to \infty} \frac{2^k}{k}$$
That is the ratio between them, in the limit, has an exponential gap. As mentioned, this is called exponential speedup.


What causes this error on importing email addresses?

Question: I'm getting some (maybe 5%) email address imports rejected with the message "Matching this contact based on the de-dupe rule would cause an external ID conflict" The email addresses in question can be updated in the UI without a problem, and I can't see that adding these rejected email addresses could cause any conflict. The supervised dedupe rule is 'Name and email'. What's the cause of this error? (Changing the dedupe rule to bypass the problem doesn't work so I'm thinking this might be a bug) Civi is at 5.11.0.
Comment: I added an External ID dedupe rule but same result. Looking at 8 examples, 7 of them were adding a home email address when there was already a main email - perhaps this is a clue. I set 'No duplicate checking' and retried - and all were rejected as duplicates!  Something wrong here...But all these emails can be added without a problem using the UI.
Comment: Andy - I can't spot that you stated the obvious, so i will ask, does your 'import' of emails contain a field for External ID?
Comment: Yes it does, should have said.
Comment: can you set up a dedupe rule for External ID and use that instead? i don't quite follow what is happening tbh since if you are importing External ID then that is the field it should be matching on, and it should not be overridden by a dedupe rule imo
Comment: I get this as well with an external ID dedupe rule, seems like a bug.
Answer: I had the same outcome when I imported external ID, first, last name and a physical address update. My dedupe rule only contained 'external ID'. When I removed the first and last name the import worked.


What is the evolutionary advantage of having pubic hair?

Question: Only humans have pubic hair. What is the evolutionary advantage in having it?
Comment: Not true. As far as I know marsupials have pubic hair. (e.g. *Macropus eugenii*)
Comment: I have no evidence, but it would provide a visual cue about maturity and fitness to potential mates.
Answer: Many consider pubic hair to be a sort of protection or warmth, however this can only hold true for the vagina, since pubic hair doesn't offer any additional protective advantages to the male urethra. The most prevailing theory is that simply it is one of the odor producing parts of the body and humans (like most life forms in general) are simply aroused by strong smells. Also most odour producing parts are usually accompanied by hair in order to "catch" pheromones. It is notable that those odours are not the direct product of glandular secretions, as those secrations are in fact odorless. It is their combination with bacteria that gives every person a unique smell. This unique smell gives a lot of important information to the canditate sexual partner. Here is an interesting study about odour importance in sexual reproduction as well as the role of MHC(Major Histocompatibility Complex)
If you are interested you can read further for for the Importance of smell in sexual production
Comment: So in short the pubic hairs catch pheromones that combine with bacteria to give potential sexual partners information. But what is the evolutionary advantage? Are you saying that this applies to other mammals too, but since they tend to have a lot of hair all over their bodies they don't need special hairs by their genitals as humans have got?
Comment: There isn't a definite theory as to why pubic hair exists.The evolutionary advantage -if any-is exchanging information. The study explains this very thing. Individuals strongly prefer a partner with smell different than theirs.This leads to MHC-heterozygous offspring, which in turn means they are better protected against a wider range of parasites. Still, like no one is completely sure what is the significance of pubic hair. Most likely it is simply catching pheromones.
Comment: And as to why swe are the only animals having pubic hair, we are one of the few hairless mammals, so we need some areas covered with hair. Most probably this area was selected because it was warm and close to the genitals (so strongly linked to sexual activity).


How to Compile Different Sketches in Different Visual Studio Code Workspaces

Question: I'm using Visual Studio Code with the Arduino extension. I have two workspaces each with a different sketch file loaded - Sketch_1 and Sketch_2. Sketch_1 will verify and upload properly. When I click on the Verify to compile or Upload buttons for Sketch_2 in its workspace, VS Code verifies and uploads Sketch_1, not Sketch_2. Am I doing something wrong, or is it not possible to separately Verify and Upload different sketches in different workspaces?
Answer: The first time you verify your sketch you are confronted with a list of available sketches (INO's). As soon as you select one of these it gets stored under "sketch" in .vscode/arduino.json.
If you zero this, "", you'll once again be asked which sketch to set as "main sketch".
This "device context" is stored per workspace so you might consider narrowing your scope when opening a folder. I know this is no fun when exploring, and the will to switch and try different examples is big, but currently there are nothing that facilitates a smoother alternative.


How do I punish my 4-year-old for biting at school?

Question: My 4-year-old daughter got in trouble for biting today at school. She's been struggling behaviorally in school for a while now. I'm not sure if it's appropriate to take toys and TV from her and if so how long? I'm just sort of at my wits' end in general and I'm worried I may be punishing her the wrong way making things harder.
Answer: At four, there's not a lot of point in "later" punishments.  Your child isn't thinking about long term consequences; she is acting in the moment, primarily.
Issues like biting need to be handled in two parts.  One, they need to be handled in situ when they occur.  That's going to be up to the daycare/school, of course, and you might want to talk to them about how they handle it at the time.  In particular, you can talk about how you and they can handle biting situations identically (when it occurs at home or out with you).
Also, though, make sure that the daycare/school is doing the right thing when it happens; removing her from the situation, getting her to a calmer place, rather than attacking her mentally (or physically, god forbid) and making the situation worse.  She's biting because she's stressed and frustrated; they should be taking steps to reduce the stress in the situation, not increase it.
Two, you need to work with her to give her tools to handle being frustrated.  That is something many children struggle to deal with; often the options are lash out or bottle it up inside, and neither of those are good (and I'd say bottling up is probably worse, at that age). Talk with her, at a relatively mature level, about how she can handle being frustrated.  Role play with her.  Show her in your behavior how to handle being frustrated, and point out to her both when you do so effectively and when you fail (afterwards, of course).
The key here is to treat this as something she needs to learn, not something she needs to be punished for. She is four years old, and having problems with something that many adults still have problems with (if not the precise same response, very similar).  Give her the tools to handle frustration now, and she'll be a much better person for it - and hopefully lessen, or stop, the biting incidents.
Comment: Couldn't agree more. The only thing I would add is giving the child a rich age-appropriate emotional vocabulary; feelings, including frustration, are hard to identify and deal with if they have no understandable names.
Comment: You can support your day care's efforts by making sure that she knows reprimands by the teacher on-the-spot will have consequences when she comes home.  We really liked when our schoool started sending home daily "report cards" broken up by time section (early morning, 1st recess, late morning, lunch, etc)  We created a positive reward system at home that was fueled by report cards (ie, two days without frowny faces means we get to go to McDonald's on the weekend, all week with no frowny scored him a bouncy house session, etc)
Comment: Excellent answer. Just one thing to add. You may want to consider trying some sensory items to be used in the mouth. For example, there are specially made plastic chew sticks. Some have flavors.  In the U.S., at least, the person at the school who may be able to help with this is the occupational therapist.  The idea here is to offer a substitute behavior.
Answer: I think you are making a mistake by focusing on punishment. Your goal is a better response to frustration. Punishment might be a part of your plan, but then again, it might not.
You need as much information as you can get about what led up to the problem an how the school handled it. Then you need to work with your daughter to react in an appropriate way. Repeated role-play with her, going through the situations so she can practice how to deal with her frustrations.
Answer: Kids this age act irrationally.  They're uncivilized and it's your job to teach her how to be a decent human being.  Rough-housing at home is a great way for kids to learn rules about physical interactions so they can be properly socialized.  Most kids are starved for this kind of play and it's absolutely crucial to their development.  When kids start hitting or biting during rough play, the play stops abruptly.  This teaches your child that if they want to have fun, they have to play by the rules.
Rough play should come naturally to you as a parent, but if you are worried about the risks or the rules there is plenty of material online to point you in the right direction.  Here's an article from a quick google search:  https://raisingchildren.net.au/preschoolers/play-learning/active-play/rough-play-guide
With my kids it usually involves lots of wrestling, tossing the kids onto the couch, and lots of tickling.  Dads are good for this sort of play because they're usually good at letting the kids take some risks that mom might not be okay with :-).


Does a provisional patent have to be filed through USPTO?

Question: I have read on the poor mans patent, but I am wondering if there is any legal backing for a idea that was written in a document and stored on a local file system. I do realize that this is faulty because the date and what not can be forged on the local file system, but does it merit any sort of legal backing. Are provisionals filed through USPTO the only ones that are recognized?
Comment: This is a common issue for solo inventors, as the patent process can quickly get expensive.  The advantage to provisional applications is that they are not public, so, if you ultimately decide it's worthwhile, you could always file an international (PCT) non-provisional.  It's worth mentioning that you could also simply keep re-filing the provisional each year, and only do a nonprovisional if it becomes necessary.  Not an optimal solution, but this question relates to the "poor man's" options.
Comment: @DukeZhou  Your comment is worthy of being an answer.
Answer:
I am wondering if there is any legal backing for a idea that was written in a document and stored on a local file system

No, especially now that the US is in a first-inventor-to-file regime. Documenting that you conceived of it first did have relevance pre the AIA patent law in 2012. Who was first to conceive  is no longer relevant.
The only way your own documentation of your inventive progress can help you is if you told someone about it under a condition of confidentially and they filed, stealing your invention. You could try to use whatever evidence you had to show that they derived it from you.
Comment: Contrary to the worryingly lax use of terminology on that blog, the UK doesn't have a provisional patent application, and hasn't for some decades. It has only one type of patent application. Because the fees don't have to be paid for the first 12 months, some people insist on calling a patent application filed without fees a "provisional patent application". This is improper, since actually it is searched and examined and can result in a granted patent.
Comment: I edited in part of the question because that's what you are answering with no and the answer to the question in the title would be yes ;) it was a little confusing this way
Comment: thanks - I was answering the first sentence which was the question "does it merit any legal backing [?]". It did not have proper punctuation but was a question.
Comment: Thank you for clarifying -  Lax language about patents is dangerous.
Answer:
Are provisionals filed through USPTO the only ones that are
  recognized?

In a word, yes. As George White said in his answer, the US and pretty much the rest of the world works on a first to file system. To gain patent protection, you must first file an application with a patent authority. In the US, that is the USPTO.


install package in subfolder

Question: At the moment I have some modified and some of my own packages placed in the same folder as my tex file. I would like to move all of them in a subfolder called packages so that I have a better overview over my files. Is there any way to achieve this?
Comment: that is something I already tried and didn't seem to work correctly, since it gives me the warning `You have requested package 'package/name' but the package provides 'name'`
Comment: you can always reference packages in a different directory by `\usepackage{/path/to/package/x.sty}`. Alternatively you can add them to your local texmf tree and use them that way.
Comment: @maetra: That is just a warning, the package is indeed loaded. (But see the other answers, which are "more proper" [with no offense to wh1t3 intended].)
Answer: befor you run pdflatex do a export TEXMFHOME=packages/
Answer: For all my larger LaTeX projects, I maintain a project-local texmf subfolder for exactly this purpose: own and modified packages, new versions of packages that are not yet part of major TeX distributions, and so on. I include this folder by setting TEXINPUTS in the project's Makefile or manually in bash: export TEXINPUTS=./texmf//:${TEXINPUTS}.
(Note: The double slash // makes LaTeX to search subfolders as well. If the project-local texmf folder contains also bibliography-related packages, such as a new version of biblatex, one also has to set BSTINPUTS accordingly.)
One often hears that additional/own packages or updates to existing packages better go into the machine-wide or user-wide texmf tree. This might work well if you work alone on a project on a single machine only, but it certainly does not work so well in a collaborative setting.
By maintaining all "non-standard" packages in a project-related texmf subfolder, I can put everything together into a version control system (such as git or subversion). Collaborating colleagues (even those that are still stuck to TexLive 2010) can check-out and built the project without having to manually install or update a dozen of LaTeX packages.
Comment: @einpoklum: _That seems like overkill, really._ – yes, it does. Until the day you have to rework a ten years old project, work on the same project on three or more different computers using different environments, work with 10+ people on the same project, or just have to pass the thing in a "way that works" to your colleague or boss.
Comment: That seems like overkill, really.
Comment: that was pretty much idea too, since I am already using subversion in a collaborative setting. But I am using windows and miktex-portable, so I have to adapt your solution. I tried to do `set UserRoots=\packages` and `set texmf=\packages` but had not success with that.
Comment: Fair enough :-(
Answer: For MikTeX-Portable there doesn't exist such a simple solution as described by Daniel and Herbert, but adding the packages' path via MikTEX->Options->Add Root seems okay. One just has to take care to remove the additional path before compiling other projects that don't use the the modified but the original packages.

install package in subfolder


Is changing the priority of a game's process to realtime bad for the CPU?

Question: On Windows I have frequently changed the priority of a games process to 'high' or 'realtime' to get a performance boost. This has never resulted in any problems with my hardware. I was thinking that maybe I could do this on Linux using the chrt command to change the realtime priority of the games process, as reniceing, even to -20 (the highest priority) doesn't seem to provide any noticeable boost. However, I am wary of doing this without knowing whether it might be bad for my CPU. Can anyone inform me on the risks?
Comment: I believe that if any real time process decides to use all available CPU (due to, for example, bugs that leads multiple threads into infinite busy-wait loops), it would remain scheduled on all CPUs *to the exclusion of almost everything else*. You wouldn't even be able to open a terminal window or SSH in from elsewhere to kill the runaway process(es).
Comment: Any modern OS does a form of time-sharing, so 'priority' simply means they get more time slices than things with lower priority.  Anything system-related should always be of the highest priority (think disk I/O and such), so there should be no way to hurt the CPU.  Meanwhile, if the game is your only user process then changing the priority won't make much difference anyway.
Answer: Changing the priority of a process only determines how often this process will run when other processes are competing for CPU time. It has no impact when the process is the only one using CPU time. A minimum-priority process on an otherwise idle system gets 100% CPU time, same as a maximum-priority process.
So you can run your game with a higher priority, but that won't make it run faster unless something else on the system is using a significant amount of CPU time.
I recommend keeping the priority lower than the X server, because if the X server wants CPU time, it's likely to be because the game is asking it to display something complex, and display is usually a CPU-demanding task (but it depends how much of the work is done in the GPU — CPU priorities have no influence on the GPU).
CPUs are designed to execute code. Changing process priorities won't affect how much work the CPU does, but even if it did, that wouldn't damage the CPU, it would only make it run hotter and so make the fans in the computer blow harder.
Comment: There are a lot of things in computer nomenclature, but it still really baffles me that pretty much *everyone* new to this concept to think "priority" means some kind of "throttle" or "limit". Is the plain English definition ambiguous somehow? If I have priority over you when doing X, and you don't need to do X, then it's as if you didn't exist, right? Why do people get confused over this, do you know?
Comment: @Mehrdad My guess would be that sometimes people use "top priority" to mean "drop everything you're doing and get this done right now even if it kills you" as opposed to "do this before any non-top priority tasks". Just anthropomorphize the computer a bit and the former starts to make sense, even though the latter is what it really means for computers.
Comment: "it would only make it run hotter and so make the fans in the computer blow harder." No, not necessarily. I could have a high-priority process that sits in a tight loop, with memory accesses being serviced from L1 cache, hence little stalling. When the game gets higher priority, it could end up causing *less* heat because it's stalling the CPU for memory access far more. Priority does not correlate to CPU temperatures, or utilization--it's not a limit as @Mehrdad states.
Comment: @hexafraction, "_but even if it did_"; nobody stated that it will run hotter
Comment: @hexafraction Does an intel CPU consume less power when it's stalling on a memory access? Not that this has an impact on my answer anyway (the CPU *would* run hotter **if** the process was using more CPU time), but AFAIK it's a too short timescale to have a measurable impact on power consumption.
Comment: That's the issue. The changing of a process priority on a system that is hitting its CPU limit is only going to change what processes use the CPU, not the amount of CPU time used in a unit interval of time. My original claim with the low level details only addressed an edge case, when the priority doesn't behave as a cap for non edge cases as well.
Answer: Are you talking about altering the amount of CPU demand while it's running the thread?
Modern CPU's actually use extremely rapid speed stepping. For example if you did analysis of the clocking of an Intel Core i5/i7 you can see the the clock speeds flickering up and down really really quickly. It's part of the way that Intel can tune the performance relative to amount of power drawn. You might have loads of power available in a desktop PC but the stuff is being converted to heat when the CPU is working harder, so it's important to get the most bang per watt.
I only know this from what I have read on other gaming forums. I'm not a CPU scientist.
I don't think you'd do any damage from tuning a thread to it's maximum "nastyness". The only thing you should keep an eye on is how hot your CPU is getting, but unless you have used overvolting in the BIOS then it's pretty impossible to cook the CPU before it shuts down.
Modern CPU's are designed to rapidly change speed. Do a search for Intel Speed Stepping and 'CPU C states' and you'll see what I mean.
Answer: Using renice on a Linux program will not burn up your CPU, but it will not necessarily do what you want it to do.
Priorities have nothing to do with how fast a CPU executes code.  It executes code from programs in different priority levels equally fast.  What priorities do change is which program the operating system chooses to run when given a choice.  CPUs can only run one "thread" of execution at a time (technically 1 per core for multi-core CPUs).  If it needs to do more than that, it relies on multitasking - it switches back and forth between executing different programs to give the illusion of running more threads than there are CPUs.  When choosing how much time to give to each of these tasks, it does so using the priority as a hint.
What "realtime" means to a computer is less "run this fast" and more "do not preempt this process."  Realtime programming is very important in many fields.  For example, if I was writing software which manages anti-lock brakes in a car, I really don't want my task to run a few milliseconds late because the OS decided it needed to run a diagnostic on the windshield wipers.  Accordingly, the anti-lock brake management software in cars is run at a "real time" priority.
Truthfully, in Linux, the "real time" priority level is a bit of a misnomer.  This is because of how Linux schedules its processes.  In windows, if you have a process that is running at a higher priority, the processes running at lower priorities are given no CPU time unless the higher priority task is waiting for something -- none at all.  Only kernel processes are permitted to run over the top of a "realtime" Windows task.  Windows has a ton of bloatware running in the background at all times, so raising the priority to "realtime" prevents all of that junk from running.
However, there's an issue with this.  Sometimes your higher priority task is dependent on one of those lower priority tasks.  This is called "priority inversion" and it is a big topic in the world of multithreaded programming.  When this happens, the higher priority task can starve the lower priority task, not realizing that it is stopping itself!  In Linux, this doesn't happen because in Linux, the priorities are viewed as a way to determine what portion of the CPU is given to each program, rather than an all-or-nothing approach.  A process running at -20 gets substantially more CPU time than one running at 0, but even in the presence of a -20 program, the 0 program gets some CPU time. If memory serves, the current Linux scheduler gives a program at -1 twice as much CPU power as a 0, and a program at -2 twice as much as a -1, and so forth.  This means that 0.9999046% of your CPU time will go to the program that's at -20, but some small fraction does go to the program at 0.  The program at 0 will feel like it's running on a 200kHz processor!
If you ever want true real time, where you can prevent anything else from preempting you, you have to write a kernel driver, or you have to use a real-time extension to Linux.  Redhat has one called MRG, which permits true real time processing with Linux.  In that case "realtime" means something speicific.  Under MRG, users in the "realtime" group are permitted to use these real time extensions (which could keep the processor busy forever, because they're intentionally not using the nice friendly Linux scheduler).


Traditional Approaches to Midrash Tanchuma

Question: What do traditional Jewish sources say about Midrash Tanchuma (in contradistinction to the Midrash Tanchuma Yashan) regarding its date of redaction and authority vis-à-vis works of Chazal (such as other Midrashim).
Answer: It says in Shem HaGadolim of the Chida (Section 1 on Rabbi Yehudah Ebas and in Section 2 on Sefarim quoting Rabbi Di Lonzano) that the Midrash Tancuma we have today is not the original Tanchuma mentioned by Rishonim and before. It is a later redaction that according to some is what is left of Lamdenu.
According to many today, 'Midrash Lamdenu' has also been lost. So it is possible that the 'Lamdenu' mentioned by the Chida is some other, later text.
Comment: Mann published an edition of yelamdenu. Cincinnati 1940
Comment: @mevaqesh If memory serves, that was editing from numerous sources that said they were quoting from Yelamdenu into a single collection. It was not from a complete manuscript.
Comment: Ein hakhi nami.
Answer: Midrashim in general are nice and a good souce for Divrei Tora for the Shabes table. However one cannot bring the words of the Midrash as Halacha, unless Chazal or one of the Rishonim specifically referred to that midrash as a source of that specific Halacha.
Rashi (and many others) commonly bring Midrash Tanchuma to explain verses in the Tora, as well as a Halachic authority.
Rav Tanhuma bar Abba himslef is an Amoira so he is in fact a member of Chazal. There are however some opinions as to who assembled the Ma'amarim into the one Midrash and the date at which it was conducted. This fact greatly strengthens the idea that one (of the Achronim) cannot use the Midrash as a Halachic source based only on his conception.
The Midrash, after it's composition, was a great influence on later Midrashim e.g. Shois Raba, Bamidbar Raba and Dvarim Raba.
Comment: This doesn't answer the question as the question was about traditional sources and none are cited.


Can I use DNS over TLS or DNS over HTTPS in Tor Browser, executed from Tails?

Question: There has long been an effort to encrypt DNS queries between the client and the recursive server to increase privacy. Firefox already supports DNS-over-HTTPS. But is Tor Browser, executed from Tails, compatible with DoT and/or DoH?
Answer: Tor always uses SOCKS5 and requests DNS over Tor. This is a requirement if you want to access onion services. This is the same on Tails as it is with Tor Browser for regular Linux, Windows, or Mac.  If you use Tor with any other application outside of Tails, you have to manually make sure that application allows that kind of proxy.


how to install fedora 12 on windows 7 as dual boot

Question: i installed windows 7 successfully. When I installed it, I created 40 gb of unallocated space in the hard disk for the Fedora installation. However, whenever i start the partition editor during the Fedora installation, it says that there is no free space in your hardware, even though it shows 40gb space in the disk partition table.
Comment: Fedora 12 is going to be unsupported in less than a week. Consider using something newer.
Answer: why not try first using a Virtual Machine to play around with fedora, instead of partitioning your HD. VirtualBox is free and open source. You can download it from http://www.virtualbox.org/
using a VM is the simplest way to get an installation of linux which co-live with windows. Also, you can select a folder which you can share files between windows and your virtualized linux.
Answer: Here is a guide to installing fedora as a dual boot with windows 7.  (even though is says fedora 11 it will works for 12 and 13 as well.  Give that a shot and see what you can do.


What wavelengths are used to search for distant solar system objects like KBOs and Oort cloud members?

Question: What wavelengths of light are used/most suited to search for distant solar system objects like KBOs and Oort cloud members? I suppose they are brightest in reflected sunlight, so they are best searched for in visible and near infrared. Is that correct?
Comment: The Spitzer Space Telescope has been used to observe KBOs. Its instruments cover a range from 3 to 180 microns (mid to far infrared).
Comment: @aventurin Do you know if it was also used to search for new KBOs, or just making observations on known ones?
Comment: I don't know, but it seems that SST has not found any new KBOs to date.
Answer: Virtually all KBO searches use mosaic CCD cameras operating in the visible part of the spectrum, usually with a red filter like SDSS-r' (centered at approx. 622nm SDSS filters) on big (~4m telescopes). This is what we did with the OSSOS survey I was (lightly) involved with (http://www.ossos-survey.org/about.html). Although cold KBOs are brightest in the infrared, the background from the atmosphere is much higher which means you are less sensitive, unless you go to space (very expensive).
Also IR detectors are smaller and less sensitive than optical CCDs and much harder to make into mosaic cameras and keep cold (to increase sensitivity). This means you can't cover as much sky area per night which makes finding rare and faint KBOs much slower. A CCD and red filter is a good balance between brightness of the objects you are looking for, the sensitivity of your detector (CCDs get less sensitive as you move more to the red or blue of the green-red central part of the optical spectrum) and a low background from the atmosphere.
Comment: Great answer. Do you know why KBOs are brightest in infrared? Is that thermal radiation or reflected infrared sunlight?
Comment: Because they are so cold (approx. 50 Kelvin), the peak of the blackbody radiation is well out in thermal infrared around 60 microns


How to get the pending transactions in the whole network from ethereum?

Question: I would like to get the pending transactions in the whole network of ethereum.
For example, the transaction '0xabcdefg' is right now pending in the pool, waiting to be mined by miners, after 12 seconds, '0xabcdefg' will be packeted in to blocks.
I just want to get the '0xabcdefg' in the pool before this 12 seconds.
In a word, I would like to get a list of the waiting list of the whole network of ethereum.
What should I do?
It seems that geth, infual, and the etherscan can not get all the pending transactions, is this caused by the mechanism of ethereum?
Answer: First of all, each node maintains its own list of pending transactions.  The nodes continuously download pending transaction from each other, but this is asynchronous process and most of the time lists on different nodes differ.
Also, each node usually limits number of pending transactions it wants to store, so if total number of pending transactions is higher that this limit, the node will drop some transactions, and different nodes will probably drop different transactions.
Also, node may treat its own transactions (published by this node) differently, for example never drop them.
Also, miners may have some private pending transactions, that miner does no show to other nodes before transaction will be included into block.
All these makes it really hard to collect all pending transactions.
Probably, list of pending transactions at Etherscan.io will satisfy your needs.


What is the difference between a bogie and a chassis

Question: Both bogie and chassis seem to define the part of a wheeled vehicle that describes how the wheels are linked together. Are these terms interchangeable? if not how are they different?
Answer: A chassis is the term commonly used to describe the overall structure or main structure of almost anything. The case for a computer can be described as the chassis, as it holds/supports/contains the components which comprise the computer.
In vehicle terms, the chassis is the structure or frame to which wheels, suspension, engine, body, etc. are attached.
A bogie {wheel} (sometimes bogey) is considered a secondary load bearing wheel, often used to provide distribution of forces in a tracked vehicle such as a bulldozer. In railway terms, it is the non-powered wheel assembly that supports the rail cars and also can be used to join two cars while providing a pivot.
If you consider that the wheel alone is the bogey, the chassis that contains four of the wheels is also called the bogey, primarily in railway applications.
In tracked applications such as those used in robotics (ref: your tag), the bogey is a reference to each wheel that is non-driven or is a reference to the entire assembly of wheels.


Is the HST going to affect college or university tuition fees? Can I pay early to avoid it?

Question: I have been looking and can't find any info on whether HST is applied to college / university tuition. If so, can I pay by the end of June to avoid it?
Answer: University tuition and textbooks will remain unaffected by the HST being introduced in both Ontario and British Columbia on July 1st.
In Ontario, refer to the Ministry of Revenue's page Tax Benefits for Students.  Excerpt:

Rebates and Exemptions
The HST will not be charged on the
  following items, commonly used by
  students, that are currently not
  subject to PST, including:

Tutoring and Tuition Fees
Residential rents
Basic groceries
Municipal public transit
[etc...]


How is pattern of holes decided on rotor of disc brakes?

Question: I am designing a disc brake. I want to know the theory behind pattern of holes in the rotor in disc brakes.
Comment: That the holes "sweep" the complete pad surface after one full rotation... Also consider if the holes should be angled cf the surface to promote airflow & cooling.
Comment: Welcome to Motor Vehicle Maintenance & Repair! Are you talking about the holes to mount the rotors to the hub or gas relief holes for cooling/venting on machines surface?
Comment: Don't drill your own rotors. Here's a [couple](https://ebcbrakes.com/articles/dangerous-cross-drilled-rotors/) [reasons](https://www.cquence.net/blog/the-reason-drilled-brake-rotors-crack/) [why](https://mechanics.stackexchange.com/questions/9148/brake-rotors-blank-slotted-or-drilled). If you absolutely want the look of drilled rotors, I recommend that you buy one from a reputable company like Stoptech or Brembo. Otherwise, there's much more extensive research required for this subject, like material properties, stress, etc.
Answer: A fully comprehensive answer on this subject is probably a bit beyond the scope of SE, that said I'll see if I can at least get you started.
First it's important to understand why some designs have holes drilled in them in the first place.
Historically this was for four reasons:
1. Heat dissipation
When the brakes are applied the friction between the pad and disc surface generates a great deal of heat, if they get too hot all sorts of problems can occur - from the spectacular in the form of the pads catching fire to the potentially lethal boiling of the brake fluid  (anyone who has ever gone for a big stop when out for a spirited drive only to be confronted with brake fade will agree that this is NOT fun!). Drilling holes in the brake disc can improve the cooling to the disc and therefore helps prevent the temperatures from getting excessive.
Some manufacturers arrange the holes in a sort of outward spiral pattern - supposedly to help with the heat dissipation by working with the rotation of the disc in the airflow. Similarly to how directional tires clear water. Honestly I'm yet to see any hard evidence that it makes any difference whatsoever but perhaps someone far more versed in aerodynamics and heat transfer could explain how it does.
2. Gas venting
This isn't really an issue any more - but in the past some brake pad materials would outgas under the heat, this gas could potentially get trapped between the pad and disc, leading to reduced braking performance. Having holes drilled in the disc allowed this to escape and prevented the issue.
3. Water
Cars don't operate in 100% dry environments, and when driving in heavy rain or through puddles some of this water can end up on the brake disc, to the potential detriment of braking performance. Having holes drilled gives an easy route for this water to escape and prevents it from impeding the brakes doing their job. In high performance applications where the brakes are operating at high temperatures for more of the time the holes give the steam an escape route (like the gas venting in #2)
4. Weight
Brake discs, especially those made of steel are heavy - and to paraphrase Colin Chapman "adding lightness" is a time honored way of making a car faster. Especially so in terms of brake discs as they are unspring weight which in a performance application is very much something you want to reduce where possible. You won't save much with the drilling of holes, but you will save some - and particularly in motorsport applications that can be enough.
So what about the pattern?
Well for each of the reasons listed above you are going to want an even distribution of the holes.
Heat - if you cluster all the holes in one quarter of the disc surface then that quarter is going to cool better than the other three quarters. Which leads to temperature differentials across the disc surface, which in turn increases the stress on the metal and can lead to premature failure.
Gas Water/steam venting - these are going to build up all across the disc, so you need to have the venting all across the disc.
Weight - weight distribution across a rotating mass is complicated (and probably more one for physics than us) but suffice it to say having it be distributed haphazardly is not good.
There's other factors as well:
Pad wear - the "empty bits" of the holes don't have the same friction against the pad, therefore a pad won't get worn as fast against a hole as it will against the disc surface. So you want to make sure that each rotation of the disc gives the whole of the pad surface the same amount of "hole" - to ensure that the pad wear remains even across the whole surface.
Structural integrity - by now you probably know why holes can be a good thing, so the more the better right? Well, no. Drilling holes in a disc reduces it's structural integrity, have too many, too close together or too large and you are going to seriously weaken the disc, which can lead to premature failure.
Braking performance - as mentioned above pads pressing against holes aren't generating as much friction in those areas, and friction is what produces the braking force in the first place. Each hole is reducing your braking surface compared to an undrilled disc, and that means you need a bigger disc with bigger pads to get the same amount of braking surface back. Which is expensive, and adds weight.
Honestly.. there's probably a book's worth in this topic but hopefully this gives you some things to consider.
Comment: Re the unsprung weight - there were several cars (Alfa for one, jaguar another...) that did inboard brakes to reduce that unsprung weight but it was never popular... access probably... But plus 1 for answer.


Why not make the training set and validation set one if their roles are similar?

Question: If the validation set is used to tune the hyperparameters and the training set adjusts the weights, why don't they be one thing as they have a similar role, as in improving the model?
Answer: Idea is to optimize with regards to unseen data in each step in order to avoid overfitting and data leakage so that the final network will be most generalizable to novel data.
First, you initialize your network weights randomly. For those weights, training data is unseen so network is optimized with regards to loss function that is calculated using training data. This was the first step.
Second, you would like to optimize hyperparameters, the parameters you use to train your network in first step. The network already worked hard to do its best in the first step while learning weights. If you use the same dataset in this step, it will have even more flexibility to fit even better to training data. But this will result in high variance, and network will perform poorly on unseen data.
For this reason, you split your data into train, dev and test. Train network with train data, optimize it with dev data and finally, evaluate with test data, never touching it until the very last step.
Comment: Why would the use of the training data for hyper-parameter tuning result in high variance? You should probably elaborate on this part because it's not clear the variance of which random variable you're referring to and why that's even the case.
Comment: @crinix so you mean that dividing the training set and dev set allows overfitting to be reduced?
Comment: @nbro Optimizing hyper-parameters wrt trainingset causes high-variance and overfitting yes. It provides the model with more means to reduce the loss on training data, while increasing loss for unseen data.
OmarZayed yes.
Answer: I think this is best explained using an analogy. Also you seen to have the misconception that you don't tune hyper-parameters for training data. You want to increase the accuracy of the training set AND validation set at the same time, but the validation set is more important so you want to maximise that accuracy more.
Imagine you had a toddler, and you were trying to teach them what an apple looks like. You have 10 pictures of apples, and for 45 years you sit them in a room and show them these apples. After all this time they will get to know the apples so well, that even the minutest differences in the photos would be noticed. When you try to see how the toddler generalised (how well it can use what it saw in training to evaluate real examples), it's absolutely terrible, because after all that time how could anything be an apple but the 10 it had seen?
So to combat this, you might think to reduce the number of years you spent showing the toddler the training set (the 10 apples), maybe that will allow them to generalise better (prevent over-fitting)? But you need a way to validate that this is actually helping, on unseen data (novel apples). That's where the 5 unseen apples come in to play (the validation set). You measure the accuracy of this unseen data to get an actual idea of how the toddler has learnt, because in a real example, the toddler isn't going to have seen the apple before, so it's important to know how it will handle unseen data.
That brings us finally to the testing set. The issue with what I've described above is maybe there's some kind of bias in the validation set, maybe those apples are slightly more round than usual. Of course you want the maximum accuracy on the validation set, so you tune everything to increase this accuracy, but this incurs a bias to the validation set. Maybe the parameters you chose are good only for this validation set. To make sure this isn't the case, you try and increase your accuracy as much as possible on the validation set, then after that you test the true accuracy on the testing set. This ensures you can't just tune your hyper-parameters to the validation set and call it a day. You need real generalisation to increase both validation AND testing set accuracy.


What kinds of things can I win by gambling?

Question: What kinds of things can I win by playing the slots in Moxxi's and what combinations payout?
Answer: Compiling personal experience and resources online, I have found the following combination of rewards:

Any two with non-bell: White weapon
Any two with bell at end: Cash
x3 Bells: Lots of cash
x3 Bandits: Live grenade
x3 7's: Random Manufacturer Character Skin (i.e Tediore, Vladof, etc.)
x3 Cherries: Green Weapon
x3 Legs: Blue Weapon or Purple Weapon
x3 Marcus: Purple Weapon
x3 Borderlands logo: Orange Weapon
x3 Eridium Bar (1): 4 Eridium
x3 Eridium Bars (2): 8 Eridium
x3 Eridium Stack (3): 16 Eridium
Comment: I wonder if someone could count probabilities of every combination and average amount of money spent to get orange/eridium...
Comment: @FrantisekKossuth It may not be completely random. I've noticed some weird results by attempting to pull both leavers at the same time.
Answer: This answer by @pixel to a different question covers the slot machine rewards. Since the topic of that question is substantially different, though (how to farm Eridium), I'll reproduce it here:

According to this article the following is a list of potential payouts from playing the slot machines - in addition to randomly generated weapons and items of course;

x3 Bandits: Live grenade (Run!)
x3 7s: Customization skin
x3 Cherries: Green weapon
x3 Legs: Blue weapon
x3 Marcus: Purple weapon
x3 Borderlands logo: Orange weapon
x3 Eridium Bar (1): 4 Eridium
x3 Eridium Bars (2): 8 Eridium
x3 Eridium Stack (3): 16 Eridium (!!!!)

It is worth noting that playing the slot machines at Moxxxi's place will get more expensive as you progress through the game, yet some of the items you can win by playing the slots scale with your character - this means that playing the slots at a lower level will cost less while still potentially providing benefit to you at the later levels.
Comment: My boyfriend got 3 borderlands symbols and I think it was an Orange item. I'm not positive, but I don't see Orange items on your list and I know we got at least one from gambling :)
Comment: You do sometimes get a payout by only matching 2 of a certain symbol


Does Salesforce1 Need Chatter To Be Enabled

Question: I am new to Salesforce1. Having watched a few webinars, I am confused on whether it is mandatory to have Chatter enabled in order to use Salesforce1. Can someone please clarify what is the dependency of Salesforce1 with respect to Chatter?
Answer: Chatter should be enabled for using the Chatter feed, Groups, People and publisher actions in the Salesforce1 app. You can still use Salesforce1 to access Contacts, Accounts etc. (as well as perform CRUD operations on these objects) irrespective of whether Chatter is enabled or not. Again, integrating external apps via Canvas do not have any dependency on Chatter being enabled or disabled and would work irrespective of that.
This link provides information on which Salesforce1 features are dependent on Chatter being enabled.
Comment: Thanks! That link was what I was looking for. Appreciate the help.
Comment: If you need to open files or attachments in Salesforce1, you need to use Salesforce Files (a.k.a Chatter Files) with Chatter enabled.  I've found no other way to open files in Salesforce1.
Answer: As a follow up, effective Summer '14 you won't need Chatter enabled to use actions in Salesforce1.

If you don't have Chatter enabled at all, you won't have the Feed page in Salesforce1, but non-Chatter actions will still appear on object detail pages.
If you have Chatter enabled, but Publisher Actions disabled, you'll get the standard Chatter actions in the web app, but all the actions will appear in Salesforce1.
Actions will appear on object detail pages regardless of whether the object has Chatter feed tracking enabled.

See the Summer '14 Release Notes for full details.


Django, html tags not interpreted

Question: I am loading a text from the DB of a django project to display it in the template.
In the text stored within the data base, I added some HTML tags but it seems like the browser cannot interprete this html tags.
Here is my template:

  {{ entry.body_text }}

And I got the raw text: Hello word instead of

Hello word

What I am doing wrong?
Answer: If you don't want your HTML to be escaped, use safe filter:
{{ entry.body_text|safe }}

django doc about safe filter.
Answer: You can also try this:
{% autoescape off %}
    {{ your_html_content }}
{% endautoescape %}

From django docs for autoescape:

Controls the current auto-escaping behavior. This tag takes either
  on or off as an argument and that determines whether auto-escaping is in effect inside the block. The block is closed with
  an endautoescape ending tag.
When auto-escaping is in effect, all variable content has HTML
  escaping applied to it before placing the result into the output (but
  after any filters have been applied). This is equivalent to manually
  applying the escape filter to each variable.

As pointed out in the other answer, you can also use safe filter which:

Marks a string as not requiring further HTML escaping prior to output.
  When autoescaping is off, this filter has no effect.

See here: safe filter.
Read more about django template tags and filters: Django Built-in template tags and filters

Django, html tags not interpreted


opening links in the same window or in a new (tab)

Question: It has always been best practice to open links in the same window. Should that still be the rule now that most common browsers use tabs? Personally i prefer closing a tab/window over hitting the backbutton. What are your thoughts?
Comment: Question has already been asked: http://stackoverflow.com/questions/118567/is-there-ever-a-good-reason-to-force-opening-a-new-browser-window
Answer: If you prefer closing a tab/window over hitting the back button, then by all means, click links with your middle mouse button.  But please don't force your surfing preferences on others.  Tabs don't change this principle in the slightest.
Answer: I think consistency is the most important thing to keep in mind.  Browsers are beginning to provide ways to open links in multiple tabs regardless of the web site's design decisions, so maintaining similar functionality as other websites is probably the biggest concern.
You really want your site's core features to behave like the other sites your users visit, so they feel comfortable and don't waste time trying to figure out the differences.
That said, there are times when you should open a new window/tab vs. opening a link in the current window/tab.  For example, if the two pages (the current one, and the linked page) really need to be viewed simultaneously).
Answer: Yes, it should be the same. A new tab is more or less a new window, it just happens to be held in the same parent container as the original tab.
Answer: I think it is still in the realm of personal preference, but depending on what I am browsing I am finding more and more that I open links in new tabs.  I do this a lot when I a reading a page with a lot of related links but I want to finish reading the main page first. That way when I am done I can go look at all those links rather than trying to go back using the back button.
Answer: Are we discussing links that leave your site?  Our company benefits provider has a web site for administering our flexible spending acct.  It opens 3 separate windows from the time I login until I reach the page to submit a claim.  I have never been a fan of opening a new tab/window when navigating within a site.
Thoughts?
Answer: Some browsers actually open a new window when asked to open a new window (gasp), even if they support tabs. I usually have two or three different browser windows open, each with a number of tabs, grouped by task. If some site unexpectedly forces a new window on me, I now have to re-integrate it as a tab into one of my open windows if I want to keep my task grouping. This is a major annoyance.
If I want to open something in a new tab, I can do so myself, thank you very much. Don't try to think for the user. The only time I can accept/expect a new window is when the original site needs to stay open, for example because I'm entering text into a form but need to open a "more info" window (see StackOverflow Answer Help button).
Answer: I'm going to wear out my scroll wheel button by the amount of tabs I open. There's a great Firefox extension that allows you to close the current tab with a single keypress, and I've assigned  to it, so it's very easy to close tabs quickly.
Comment: The extension is SwiftTabs, but it's sort of out of development, and it took a fourth party to get a version working in Firefox 3, so I don't want to mention it directly in my answer.
Comment: you can close tabs by pressing the middle wheel button (scroll).. this is default behavior!


Drywall repair problem

Question: I am trying to hang window blinds, however when I drilled the hole to use wall anchors the whole space collapsed in and the space had obviously been repaired before. How can I repair this hole with enough strength to hold the blinds once they're hung. Thanks so much
Comment: The drywall can be fixed, probably requiring a board inserted behind the hole to hold the patch in place, but I doubt it would be strong enough to hold blinds. Mount the blinds on the window frame or on studs. For patching, see https://www.lowes.com/projects/repair-and-maintain/patch-and-repair-drywall/project , for large holes in particular.
Comment: Window blind mounts will a few options to mount them. They are predrilled to mount on the sides of the windows, as you have tried and there are predrilled holes so they can be mounted on the head of the window too. Then again, a picture of what you have would help....
Comment: When there are a bunch of old repairs that sheetrock has no strength. I find it best to remove enough to get back to the next stud away from the window and make the width wider 4 to 6" at least or to the ceiling and 6" below the repaired area. I think larger patches in this case are easier to hide and provide more strength than a small patch.
Answer:
Use a drywall knife or small saw to cut the hole into a square or rectangular shape, large enough to insert a length of 1x or 2x (depending upon the size of the hole, I've even used paint sticks for small holes). Use a drywall knife to gently cut into the painted paper outer layer of the drywall, angling inward toward the opening ... this makes the finish process easier ... all around the edges of the opening.
While pulling the board tight to the back of the existing drywall (board should extend well past the edges of your new rectangular hole), put in two or three screws through the drywall into the board on both sides of the hole (not too close to the edges of the hole). Be sure to sink the screws just enough so that mudding over them will leave no bump.
You can put a couple of screws partway into the insert to handle it by, if the hole is too small to just use your hand to hold it in place. Remove those screws before setting the patch piece.
Once the board is secured, cut and insert a matching thickness of drywall. the closer to the same size, the better.
Use a drywall knife to gently cut into the paper outer layer of the drywall angling out to the edges of the patch piece.
Place the patch, securing it to the backing board you inserted with several screws (not too close to the edges).
If the patch is not a close fit, use the drywall knife to widen the angled paper edges, to make room for taping. A fiberglass mesh tape is best for this, and will hide better if the painted paper is peeled/carved from under where the mesh will be placed.
If the patch is a close fit, skip #6 and begin the fill : the gaps can be filled directly with goop (drywall mud). Expect to do several layers (especially if mesh is used). First push the mud into the gaps and let it dry, then put a second layer. Finally, a third finish layer.
Apply mud with a wide, fresh edged drywall tool . Use the tool (and a damp rag or sponge) to keep the mud fairly smooth for the first layers as you are applying. For the finish layer, carefully smooth out the finish (don't forget to also mud your nail heads on the patch during the first round).

Most people apply the several layers of mud, then use sandpaper to smooth out the fix, leaving a smooth flat fix in a textured wall. I generally use a wet rag or sponge during the process to keep the extra cleaned up as I go. If the wall is textured, a rag or sponge matching the texture is helpful to re-create the texture of your fix. After the final layer is applied, press the sponge or rag gently onto the patched area to leave a matching texture!
Be patient : let each layer of mud dry. Also, be patient : don't try to paint before the entire project is thoroughly dried, or you will wreck your beautiful work!  Use a primer on the newly mudded area before applying the matching paint.

Drywall repair problem


How to get list of spfx extensions available for my SharePoint online tenant

Question: Very happy new year to all. As i am working on modern experience. I was going through the Microsoft road map. there i found that they have rolling out some of new extensions. How can i check that is available for my tenant.
Is that possible to have a list of extensions i can use for my tenant.
We have Application Customizer, Command Set, and Field Customizer categories.
Answer: Currently, the SharePoint Framework includes following three extension types.

Application Customizers
Field Customizers
Command Sets

Per my research, there are no other new extension types. Learn more about SharePoint Framework Extensions.
When create a new extension by running the Yeoman SharePoint Generator, it will promote "which type of client-side extension to create". It lists all extension types you can create.

I suppose that you are reading SharePoint Framework roadmap. This is a list of areas that SharePoint engineering has in the backlog and is looking into. This does not mean that all of them will be delivered, but they are looking into getting items and topics from this list gradually released with the future releases of SharePoint Framework.


Pros and cons of refactoring code during testing phase?

Question: What are the pros and cons of refactoring code during the testing phase? Are there any set methods of doing this?
Answer: You avoid this question completely by integrating testing into software development life-cycle. I assume you mean that the bulk of testing is done after development, rather than "how do we re-factor in the 11th hour of final testing"?
General advice for re-factoring is to have good test coverage so changes can be made with confidence and have a high degree of automation so more tests can be run quicker.
Answer: Unless you have a really really strong reason to refactor during testing and the unit/functional/acceptance test to check your changes, I'd say don't.  Nathan Cooper points out that good code coverage will ease this pain of refactoring and I agree. Your question implies a distinct "code then test then deploy" workflow so changing stuff in the coding phase is going to draw out the testing phase.
Pros:
- Your code will be better organized after refactoring, though by definition, it won't be any more functional than it was before the changes.  Refactoring is just to change the structure of the code base, not its behavior.
Cons:
- You can potentially introduce bugs that your tests won't catch.  Remember that any time you make a change, there is a potential to introduce a bug.
You'll have to calculate the costs associated with the risk of introducing a new bug during the testing phase.
Answer: In general, how many changes you tolerate in flight is tempered by your test coverage.
Imagine a case where the team wants to complete a large refactor while implementing a new large feature.
If you have robust test coverage, then this case may not be daunting. Presumably because the cause of errors can be identified with higher speed and certainty.
However if you have anemic test coverage, then this case may be horrifying. Presumably because the cause of errors consume more investigation effort.
To answer the question of pros and cons:
Pros:

Greater velocity

Cons:

Greater risk


What are the keys corresponding to the shortcut?

Question: I'm trying to figure out how to use my Apple keyboard at times instead of the mouse. What keys do I press for the following shortcut?
Answer: Apple's Help menu in the finder has an article titled What are those symbols shown in menus? - the related articles at the bottom are great reading. Your specific answer is:
shift+fn+delete
The up arrow ⇧ is the shift key and the symbol ⌦ is the Forward delete symbol.  Typed fn+delete.
Refer to Mac keyboard shortcuts for further information on the symbols.
Answer: The symbol with the X is the delete key, the up arrow is the shift key, a small up arrow (about the size of ^ ) is the control key, and the command key's symbol can be found on the keyboard above the word "command" on the key.  The  key is the option/alt key.
Comment: How does this improve on other answer?


Changing multiple upload text

Question: Just wondering if anyone knows if it is possible to change the text SharePoint 2010 presents when you select the upload multiple documents. Currently it says: "Drag Files and Folders here" I would like to change it to "Drag Files here" . Our business case is that our users are uploading folders to document sets which is a "No No" in SharePoint 2010.  I realise changing the text won't stop them dragging folders in but at least it won't be seen to encouraging them to do so.
Answer: Upload.aspx is an application page because it is served up from the _Layouts virtual directory of the server instead of the content database. All Application pages are bound to use Application.master as master page. You simply can't change Application.master or any application pages.
Therefore, your best is to attach/insert some jQuery/Javascript using Custom Action and ScriptLink, which will change the text for you.
Comment: It's not recommended to change files in 14 hive but it becomes pretty much a trivial task using Javascript/jQuery.
Comment: I'm afraid he's right. I was looking if it were possible to edit the upload.aspx page in the _Layouts folder. But that does not seem feasible.

Changing multiple upload text


Migrating to WPEngine

Question: I'm working on migrating our Wordpress site to WPEngine, and I don't know how to get the civi database onto WPEngine. WPEngine doesn't allow the creation of a new database for civi. Has anyone done this before? I have found other topics regarding WPEingine here, but for now I just want to get the database onto WPEngine.
Comment: I would do extensive testing of all your current civicrm uses and all possible future civicrm uses - you may run into a ton of issues. Any reason why you chose WPEngine? (besides that they are a great WP host?)
Comment: WPE was recommended to us and it looked great until now. We're actually moving to a new CRM so using civi on WPE would be temporary. I may want to rethink moving to WPE before changing the CRM because it may be more trouble than it's worth.
Comment: WPEngine is great for WordPress hosting. Thats not to say that there arent alternatives that are great too and would work fine with CiviCRM. If you are leaving CiviCRM - **tears** - you may want to consider making that transition first.
Answer: I have only used CiviCRM at WPE on test sites.
You will have to share the same DB as WP.
You need to prepare teh backup for restore offline.   That said, I mean that if backed up from another server, the DEFINER (used in Triggers and Routines) have to be stripped out, and the database should be compressed.   You'll need to restore via phpmyadmin from my.wpengine.com
A word of warning, WP Engine reserves the right to change the database user.   When they do this they will update wp-config.php, but not civicrm.settings.php.   This has not happened to me on CiviCRM (keep in mind I only use WPE for testing on CiviCRM) , but it has happened on WP sites I have supported at WPE.
Comment: Thank you, Kevin..... So I export my database from the current host and then I have to edit it to remove the DEFINER statement(s). What's the best tool/application for editing the .sql file? Will any text editor work?

Thanks for the heads-up about the potential for a database user change! Of course, that only matters if I actually get things up and running on WPE.
Comment: we use the following perl script in case it helps your situation: perl -pi -e 's#\/\*\!5001[7|3].*?`[^\*]*\*\/##g'

Migrating to WPEngine