How can I find the Haskell source code for the sqrt function?

Question: I am starting to learn Haskell and need to learn how to look things up.
Since I am studying a function that uses sqrt, I want to see how that was made in Haskell.
This is as much an exercise in using reference material as it is in seeing how the sqrt function works under the hood in Haskell. Any advice would be appreciated.
Answer: By entering :i sqrt using ghci, we can see that sqrt is

-- Defined in 'GHC.Float'

A quick google shows that the source code repo is on https://gitlab.haskell.org/ghc/ghc.
Entering sqrt in the search bar for the repository yields several pages of interesting results (including tests). From what I see, using sqrt includes calling the corresponding sqrt operation on a CPU level (check out the x86 related code as one example).
Of course, GHC is not the only implementation of Haskell, but at least within these realms, both terms are most often used as synonyms.
Edit: OP found the implementation detail with this approach in https://gitlab.haskell.org/ghc/ghc/-/blob/master/libraries/base/GHC/Float.hs, where sqrt is defined as follows:
sqrt x              =  x ** 0.5

Comment: Thank you @Matthias Sieber
From your instructions, I was delighted to find the following in the source code.
sqrt x  =  x ** 0.5
I found that I could substitute x ** 0.5 for sqrt which tells me a lot about Haskell.
Much thanks for your help
Answer: API docs for the core libraries are maintained at haskell.org as well. There's an index link in the upper right where you can look up specific functions and then, on each module's documentation page, there are links to source code. For sqrt:
https://downloads.haskell.org/~ghc/latest/docs/html/libraries/base-220.127.116.11/GHC-Float.html#v:sqrt
Also, bookmark this, the top-level of the latest API docs:
https://downloads.haskell.org/~ghc/latest/docs/html/libraries/index.html
Comment: Great resource @dino. Much thanks
Answer: The simplest and the most effective way to learn Haskell is to use online playgrounds.
Here's how a square root integer calculation may look like in Haskell:
squareRoot :: Int -> Int
squareRoot n = try n where
   try i | i * i > n = try (i - 1)
         | i * i <= n = i

main = do
   print (squareRoot 749)


PSPACE languages reducible to other PSPACE languages in polynomial space

Question: Intuitively it makes sense that all PSPACE languages are reducible to other PSPACE languages in polynomial space. But how would I go about actually showing this?
Answer: The same way that you show that any problem in P is polytime reducible to any other, or that any decidable language is Turing reducible to any other: solve the problem in the reduction.
Note that the claims (yours in the question and mine above) aren't quite true for many-one reductions, since you can't reduce any other language to $\Sigma^*$ or $\emptyset$ using many-one reductions.


One Punch Man After Season 2

Question: I just finished binging One Punch Man Seasons 1 and 2, and I absolutely loved it. But it seems to me that the second season has an incomplete ending, and full of cliffhangers. I want to continue watching the main plot, but there are many confusing titles after the second season, and all of them are named "SPECIALS". So, which one should I continue with?
Answer: The specials are set inbetween or after the seasons, so in that sense for something animated it would be advisable to continue with the second season specials, with the chapter

Saitama and Those With Reasonable Abilities
Transcription: Saitama to Sokosoko no Nōryokumono-tachi

but those specials are mostly filler, meaning they add little to the general story and dont resolve cliffhangers. If you want something that resolves cliffhangers you won't find it yet in something animated, and you have to read the manga, or the webcomic, but the manga has become quite different than the webcomic, and it's going to be the manga what probably they use as original source material for the next seasons of the anime.
List of One Punch Man episodes
Answer: The reason why it feels incomplete it's because season 2 doesnt cover the whole arc - the arc is pretty long, so the studio decided to end season 2 somewhere after end of the tournament.
To be honest, the moment they picked as an ending for season 2 felt very random, probably production was a bit rushed.
Anyway, there's no wa to continue watching the main story.
You can try reading manga, but there's two versions: original one by ONE which is very rough in term of art, and Yusuke Murata which is an excellent looking redraw of an original manga, but the arc of Monster Association is still in progress
And as Pablo metnioned, the specials covers fillers that are mostly just silly comedy, but some are showing some backstory of characters like Fubuki or Saitama.

One Punch Man After Season 2


Are there any ways to clean a mirror without water or cleaning spray?

Question: Are there any ways to clean a mirror without using water or any cleaning spray?
Comment: It might be worth explaining *why* you want to clean a mirror without water/spray in case that reveals any better answers.
Answer: You can use a mechanical cleaning method
You don't need any liquids at all.
If the mirror is made with float-glass which is quite flat and free from ripples, you can get excellent results with a razor blade at a sharp (heh) angle to mechanically 'scrape' the mirror clean. Use the same angle as you would to 'hone' the blade but push instead of pull the blade. This technique can cleanly remove finger prints and other surface dross. If you're careful, you can clean the mirror surface with a single blade before it gets too dull.
Answer: It depends on how dirty the mirror is. For loose dirt or dried-up soap spots, wiping with a soft cloth can be enough. If the mirror is coated with e.g. sand, you need to use water to prevent scratching the mirror.
Answer: You can use lemon juice for cleaning mirrors. It is easy and usefull method for cleaning mirrors. Lemon are common thing in houses so you should use it .


countering the "softer = slower" problem?

Question: My choir has a consistent tendency -- absent a metrenome or vigorous conducting -- to slow down for quieter dynamics (and then never regain the original pace).  We have several individuals with good senses of pace; this is a collective problem.  Why does this happen and how can we fix it?  We don't want the director waving her arms that much on stage; we want to fix the root problem and perform with minimal conducting.
Answer: @Matthew Read gave some good suggestions, to which I'll add:

Try rehearsing the problem sections at a wide variety of tempos, particularly ridiculously fast (once the choir knows the section reasonably well).  Unwanted tempo changes become habitual.  One way to break that habit is to go much faster (or slower, if the problem is acceleration) than desired, at a variety of tempos, before going back to the tempo you actually want.
@Matthew Read alluded to this, but I'll expand on it.  Anytime you need the ensemble members to pay more attention to your conducting, always conduct smaller, not larger.  By conducting too large, the conductor is helping the ensemble slow down regardless of the tempo being conducted.  Keep the pattern small and simple.  In rehearsal, if you really believe the ensemble is not watching, keep making the pattern smaller and smaller, and eventually just stop conducting and see how long it takes the ensemble to notice.  After this happens a couple times, even younger students are embarrassed enough to pay more attention (usually).
Another rehearsal technique, so long as the ensemble understands it is not for performance, is to have the ensemble gently "sway" with the beat and try to keep the time moving.  The physical motion of following the beat in this way is likely to call more attention to the fact that the tempo is slowing.  Of course, rehearse without the swaying after a couple tries so that it does not become habit.
Comment: Good tips! On conducting: speed = dynamics, size = tempo. Try keeping the tip speed constant and then varying the size of your pattern. Since it takes varying amounts of time to get from point A to point B, we prove the relation between pattern size and communicated tempo. Also, a drastic change to small size can often get an ensemble's attention.
Comment: Thanks for the tips!  Conducting smaller does seem to get people's attention, and practicing (intentionally :-) ) at a variety of tempos seems like it will break bad patterns.
Answer: I can't speak to the psychological reasons or addressing them, but there are a couple things you can try that basically apply to all types of music.
1) Have the weaker members listen to and follow the stronger ones.  Ensure they can hear them, of course; don't put them on opposite sides of the stage.  The mediocre members will probably do well enough if the bad influence is removed.
2) The director doesn't need to flail in order to indicate the tempo.  Small hand movements should be enough.
3) Not everyone can keep a consistent beat, but everyone can follow a beat.  If choir members refuse to do the latter by following others or the director, they should be dismissed.  (I'm assuming your choir is "serious". If not, it may be something you just have to deal with.)


First draft Word count.

Question: Do you find your first draft is longer or shorter than your completed work?
I understand that I will be cutting alot of unnessary words, but I also have a list of things I need to add. I haven't gone back to add these in yet.
I'm finding it difficult to know if I'm doing okay with the word count. Is it okay and normal for it to be lower than than the final piece?
Comment: Hi Jessum, and welcome to Writers. While this is a good discussion question, discussion questions are out of our scope. This answer is "Your Mileage May Vary." Some writers are very verbose and need to cut a novel out of the first draft; some are very sparse and need to add a lot of detail. There is no right answer.
Comment: Hi Jessum! Welcome to Writing.SE! What kind of work are you talking about - academic writing? Fiction? Is there a word count you need to reach / stay within, or are you just observing a trend in your writing?
Comment: Sorry, I should have provided that information. Romance, fiction, and yes there is a requirement.  It needs to be within 50,000-75,000.
Answer: I think this is a matter of personal writing style.
My first drafts are typically shorter than my final drafts; even though I cut entire pages out of my first drafts, and in one case ten consecutive pages were rewritten into half a page. (In the first draft, I had a plan for a secondary character that didn't work out, it just didn't fit right. I deleted him and his introduction and dialogue, and the slack was taken up with a different character.) I also cut any unnecessary exposition, if it feels boring I rewrite it.
However, despite all that cutting, as I re-read scenes, I often consider them under-imagined, without enough imagery, color (literally color of the scene being described), feelings or emotional context, and so on. I see places where my dialogue is too blocky; just people talking, and that needs to be broken up with some stage craft, action, pauses, thinking, and so on (a wall of dialogue is an under-imagined scene; people DO things as they talk). So I fill them in.
That makes the story read and flow better and it increases the word count; often by 20%. Although you need to hit some minimums to have a novel, I wouldn't worry too much about word count. Write and rewrite until the story reads smoothly to you, cover to cover.
Which is how I rewrite, cover to cover; it gives me enough time between revisiting scenes so I see them with fresh (and more analytical) eyes, so I can tell if they are boring, or awkward, or need work. For me, usually by the sixth draft I read through the whole thing without a hitch, then I'm done and its ready for the next step. I don't limit myself to six drafts, my first book I probably did 20 drafts before I was satisfied. But now six is typical.
Answer: Word counts are dangerous. Very dangerous. The reason is that you have an element entirely alien to the creative process (as well as external to it) which takes over.
Indeed, I was talking with someone the other day about a well-known TV series (doesn't matter which; they all fall for the same trap) which was supposed to be 1 season, then it became 2 and now there are plans for more. Ironically enough, it's based on a book and the events described in the book are already dealt with in season 1.
Can you imagine being a writer of a TV series, with some producer over your head telling you, "I don't care what you'll do, make me episodes that don't resolve anything for as long as I tell you. Then, I want you to wrap things up in 8 episodes."
Obeying a word count blindly is a similar trap. Now, the operative word here is blindly, There are indeed purposes in having a word count, mostly marketing ones though, but perhaps it can also be an indicator for less experienced writers as to whether their story has come full circle. If you think you're done with 30.000 words, something probably isn't right.
So, to answer your question after this long but necessary detour, a first draft is basically a very extended outline of the story. It helps you visualize what's there. Now comes the next step, formulating the story into a narrative, which is an entirely different animal. It doesn't matter how long or short the first draft is. Some things will have to go, some things will have to be added. If your final draft word count varies by more than 25.000 words from other works of your genre, then you could perhaps ask yourself whether you've been either too laconic or too verbose. But certainly not before the final draft.
Answer: Many professional writers and editors report that there is about a 25% loss between the first finished (!) draft and the final draft.
Depending on your approach (e.g. either outlining or pantsing) and your experience as a writer (is this the first book you write and you have to find out how to do it as you go along, or do you know the next steps?), your very first draft may be very different from the first finished draft, or it may be the first finished draft.
Since you plan to add in material, it seems to me that you are both inexperienced and didn't plan your story beforehand (at least not in detail), which makes guessing the final wordcount rather impossible.

Please not the difference between "first draft" (which is the first version of your story that you write) and "first finished draft" (which is what you send in to your editor or agent).
Comment: A very first draft. I have a plan but while actually writing it some areas seem out of place or unauthentic. I have writing experience, but not in this genre or being required to stay within an exact word limit.

First draft Word count.


Tile floor installation on top of hardwood

Question: Can I lay the backerboard for a tile floor on top of hardwood floor that is glued to 3/4 inch plywood subflooring?
Answer: Yes. Just make sure you use fiberglass mesh on top of the backer and use a good quality polymer modified mortar to install the tiles.
Backerboard subfloors are a cheapout way of avoiding the installation of a proper lath and mortar base (there is simply no comparison). If you choose this route, there is nothing to bind the floor together (which prevents cracking). using a fiberglass mesh interface membrane will help to act as a mechanical binder for the tile floor to be laid.
The use of polymer modified mortars instead of simple cementitious mortars makes a huge difference in how well the wet "stick" of the tiles makes sure there is a high percentage interstitial bond between the tile and the subfloor. This makes sure that once it sets up, the tile has no ability to move in relation to the mesh/backer assembly. This ensures that even if there are minute voids between subfloor and the backer--the footprint of the tile is spread as wide as possible through the backer to the subfloor. The intention of this approach is to remove any chance of decoupling of the tiles.
Answer: You're going to end up with a big edge wherever you transition to the rest of the floor - between 3/4" to 1" depending on the backer board, tile, and trowel you use.


Filament feed tube

Question: I'm new to 3D Printing and recently purchased an Ender 3D PRO I'm having an issue with the filament guide tube getting pushed out of the nozzle on the feeding mechanism.  The assembly instructions don't include a whole lot of detail about installing this guide tube but there are blue clips that were included along with the spare nozzle.  There are no instructions on where to use these blue clips and I have a hunch this might be the problem.
Answer: The blue clips stick in the connector on the extruder end of the feed tube. They are to keep it from opening as the printer extrudes and retracts filament.
To install them, push them in between the white part of the fitting on the feed tube (not the hot end). You should only need one or two, and they are all of varying thicknesses. If you're not familiar with these fittings, I found a YouTube video on how to use them.
Answer: The clips or collet clips as they are called are to secure the Bowden tube more solidly to improve printer extrusion; more specifically: extruder retraction performance.
E3D has explained this very nicely on their site under Bowden tube physics:

For the bowden couplings (which can have some wiggle room in them) we are introducing collet clips, which slide under the toothed collet part of the coupling that physically holds the tube and locks it into place with a little pre-tension to boot. This reduces coupling lash to near zero as the collet and tube it is holding are locked into place.

From the animated gif from the E3D website (animated gifs are not allowed on SE) it can be seen that without clips, the tube can move in the tube coupling:

Filament feed tube


What is the IIS7 default keepalive time?

Question: What is the IIS7 default time for HTTP keepAlive?
Answer: The default connection timeout in IIS7 is 2 minutes.  Click on your web site in IIS Mgr, click Advanced Settings, and expand Connection Limits.  The Connection Timeout (Seconds) setting is what governs this.  If IIS doesn't receive activity on a connection for this duration then it will time the connection out.  This is regardless of whether or not the connection was requested as a keep-alive.  You will, of course, have to have keep-alives enabled for this to be a "keep-alive timeout".  Keep-alive is enabled by default in IIS.
You can also set it for the site in the applicationHost.config file using the <limits> and the connectionTimeout attribute.
<limits connectionTimeout="00:02:00" />

This will set the timeout value to 2 minutes.
Answer: HTTP KeepAlive is a true/false switch. If HTTP Keepalive is true, it will use the "Connection Timeout" setting (default 120 seconds)
Answer: Also you can use this option in your web.config
<system.web>
    <httpRuntime executionTimeout="180" />
</system.web>

https://msdn.microsoft.com/en-us/library/e1f13641%28v=vs.85%29.aspx?f=255&MSPPError=-2147217396
Comment: +1. By the way, the link you have there is for .Net Framework 3 which doesn't actually support an int for that attribute. I think you meant this link: https://docs.microsoft.com/en-us/previous-versions/dotnet/netframework-4.0/e1f13641(v=vs.100)


How to get to Soltheim on Skyrim?

Question: I have seen many explinations saying "go to a city and finish dragons rising" problem is that I had already completed dragons rising before I downloaded the DLC. How do I fix this. (There is no boat at the Windhelm docks)
Answer: It wasn't clear whether you have been attacked by cultists yet - if not just wait until you are attacked by cultists - in the next town you enter. That attack (which is easily defeated) will result in you coming in possesion of a note - and the existence of the ship at windhelm.
Answer: Here are the steps to get to Soltheim:

When you get attacked by Cultists, kill them then loot them. This will also start a new quest called "Dragonborn".
One of the cultists will have a letter, read it then you will get a new objective. The letter will also tell you where to go and how to get to Soltheim.

How to get to Soltheim on Skyrim?


Can I claim spouse exemption for my dual status alien spouse?

Question: For the 2014 tax year my alien spouse and I (US citizen living overseas) will file 'Married filing separately' because she is making a 1040NR expatriate return, which will include f8854. She is a resident alien for Jan-Jul 2014 and a non-resident alien effective mid July 2014 when her I-407 is accepted at the US consulate.  During 2014 she will have no US source income, but will receive foreign source income throughout the whole year.  Can I claim a 'spouse exemption' on my 1040 if she does not claim a personal exemption for herself on her 1040NR?
Answer: Here's what the IRS pub 501 has to say on the matter:

Separate return.    If you file a separate return, you can claim an
  exemption for your spouse only if your spouse had no gross income, is
  not filing a return, and was not the dependent of another taxpayer.
  This is true even if the other taxpayer does not actually claim your
  spouse as a dependent. You can claim an exemption for your spouse even
  if he or she is a nonresident alien; in that case, your spouse must
  have no gross income for U.S. tax purposes and satisfy the other
  conditions listed above.

Since your wife does file a tax return - you cannot claim her exemption.


Ps4 gameshare download

Question: I'm gamesharing with a friend on ps4. I set his account as primary on my ps4 and he put my account as primary on his ps4. He downloaded a dlc for a game that I want to download. I have one he wants to download. The game has a lock next to it and will not let us download it. What do I do?
Answer: The account that purchases the content will need to perform the download/install on the system before the guest/alternate account can access the content.

Ps4 gameshare download


Can Bongos be Safely Incorporated into a Normal Drum kit?

Question: I recently obtained an oldish pair of bongos, in good shape, and would like them to be part of my drumkit. But - they have animal skins, rather than the plastic heads found on most drums. That means they maybe won't take kindly to being hit with sticks rather than hands. Will they suffer, or perhaps get played with different sticks? What experience do any readers have to share?
Comment: Skin age may be a factor in this. I've 2 animal skin djembes & with nothing but time, one skin failed at 20 years. The other is still good after 30 years. As regards storage, they sit next to each other in the living room, so I'd consider their treatment 'identical'.   One was a couple of hundred quid more than the other, which may go some way to explaining why the cheap one failed first. My bongos are plastic skins so I can't really compare.
Comment: @Tetsujin as you've probably considered, the skins may well have undergone different preparation or endured different storage conditions, or both, before they got to your living room, which would very likely account for much of the difference in durability (and some of the difference in price).
Comment: @phoog - absolutely. One was bought in a posh music shop in the centre of London, the other from an African market. One can easily speculate the manufacture was likely 'different'. I suppose I should have said 'quality' rather than just 'age'.
Comment: I did a bit of research, finding that synthetic drumheads were developed during the 1950s, but I decided not to post an answer based on this fact because a natural head on a snare drum (or on any other drum intended to be played with a stick) could still be significantly different from the ones on your bongos.
Answer: First, I'm not a percussionist but I do know a decent amount about Latin percussion so here goes: Bongo skins are thin but the skins that are made for companies like LP and Meinl are pretty durable. Also remember drum heads used to be made from calfskin (and still are!) If you're not doing any serious banging and you take a sensible approach you should be fine.
There are also synthetic heads made for bongos and congas that are much more durable if you're willing to invest a bit. Many pro Latin percussionists I know have switched to synthetic heads for their feel, durability, tone, the ability to hold its tune and not having to detune them when not playing. Here is an example.
One thing about bongos is by playing them with sticks you lose a lot of the nuances that you get by playing with hands and fingers, like slap and muted tones for example. It is a nice color to add to a drum kit though and I know some guys that have done it.
Comment: "lose a lot of nuances": One can touch the head with one hand, or even with one stick, while striking it with the other stick, though it is perhaps impractical to do a lot of this if you're very busy with the rest of the kit.
Comment: @phoog That still doesn't come close to what a bongo player does with his hands and fingers.
Comment: Of course.  But it is a way to achieve a degree of variation that is not possible with sticks alone.
Answer: You can add bongos to your drum kit and hit them with sticks, if you're willing to accept a little risk.  Yes, the drumheads will wear out faster, since they are not meant to be hit with sticks, but the heads still should be pretty durable, and you may be able to replace them with regular coated drumheads.  The 8" head will be easy to find, the 6.75- maybe not so much.
There was one Drum Corps group (I can't remember which one!) that replaced one of the small drums on their marching tenors with a bongo.  These bongos took much more abuse than they would on your drumkit, and they must have worked well enough, since the instruments survived shows and they never scrapped the idea.
I'd be more concerned with the bearing edge of the drums, which is the wood rim that the drumhead rests on.  The bearing edge is pretty exposed on a bongo, and accidentally hitting it can damage the drum itself over time.
Answer: Bongos are used as part of drumkits, but there are certain provisos.
Since they have no rim, like a snare has, care needs to be taken not to hit the head like a rimshot, striking the bearing edge. The wood underneath at that spot will get dented, and the head itself will wear quickly there.
The head itself isn't much of a problem, after all, earlier drum heads were made from vellum, before being plastic.
While sticks can be and are used, mallets, tymp sticks or rutes are going to be kinder to the bongo. Timbale sticks or conga sticks work well, but again, avoid hitting the bearing edge. Skin heads are more susceptible to temperature and humidity changes, and won't be as easy as a tuned drum to reproduce exactly the same sound wherever they're struck, due to differing thickness across the heads, although that's a small problem.
Evelyn Glennie uses bongos as part of her percussion set-up, playing them with standard drumsticks.
So, bottom line - yes, they will survive, if treated respectfully, but consider using them as they were designed - played with fingers and hands. They would still be part of the kit, but used for their original purpose.


Can a KVM switch be vulnerable through a VGA port?

Question: I have one KVM switch that has a VGA port to connect monitor.  I want to know how to test that the KVM switch has no vulnerabilities by this port (using DDC)?
Answer: There are I2C lines in the VGA port, that are used to identify which display is connected (maximum resolutions, etc) and to control it if it supports DDC. Thus, bidirectional digital communication is possible.
On the computer side, there could be vulnerabilities in how it parses the EDID sent by the device connected to the VGA port. That could be used to execute malicious code.
On the display device/KVM side, it depends whether a smart device like the main CPU is connected to the I2C bus or if it's just a dumb one like an EEPROM (you can get away with connecting an off the shelf I2C EEPROM with the EDID data in it). In the former case, there is software that interprets the data sent by the computer over I2C - this software could have vulnerabilities and once you can achieve code execution on the KVM you are free to rewrite its firmware to persist. In the latter case, there is no smart device to compromise and you can write a malicious EDID that exploits bugs in connected computers and hope a vulnerable computer is connected.
Comment: @Juliet Creating malicious EDID means you need to find an exploitable vulnerability in the EDID parser. No one is going to drop a 0day just to show how to do that.
Comment: Hi. Thanks, how can we use this device?and how create malicious EDID and exploits bugs in connected computers?
Answer: I don't think it is even possible to use VGA to attack either the monitor or another PC. VGA can only send analog data, which is a one way transmission. As long as this is pure analog data, the monitor itself cannot be exploited either.
Other devices suchs as a mouse or USB stick connected to the KVM can be exploited to store malware and trigger it on a second machine.
If I have misinterpreted your question, please provide additional information.
Comment: Thanks for attention,I have kvm switch that support monitor sharing. I want to test data leakage in DDC. first I want to test VGA have vulnerability? And how to test is there data leakage in DDC?
Comment: Well, DDC is the serial version for VGA.  Therefore it is not really analog data.  But then again, a serial connection is not much different from analog data for exploitation.
Comment: HI. Thanks . mouse and keyboard in this KVM are PS2. How to can use PS2 port for malware and trigger it on a second machine ?


How many particles can a particle accelerator accelerate at once?

Question: Does a particle accelerator lose its accelerating effectiveness as the number of particles being accelerated increases? According to Wikipedia, the mean acceleration of a proton in the Large Hadron Collider is 190,000,000 g's. Could the LHC accelerate one gram worth of protons at the rate while using the same amount of power?
I suspect not, but I don't know why.
Comment: Keep in mind that particle accelerators are not just about quantity -- quality is also a concern. The ultimate objective is to collide beams together, and thus there are a whole host of more subtle issues that come along with that.
Comment: For the LHC about 300 trillion in each beam.  But if you were to slow them down and allow them to form a gas at normal temperature and normal pressure, the gas would occupy a space about one hundredth the size of a grain of salt. [Everything you wanted to know about the Large Hadron Collider: BY THE GAZETTE (MONTREAL)](http://www.canada.com/montrealgazette/news/arts/story.html?id=f8b84761-ef5a-45c0-ab3e-9b5ce6497088) .
Comment: Excuse me to ask some spin-off from that question here: is it possible to accelerate neutrons (as prototype of simple and neutral particles), and if so, how?
Answer: In general the total voltage $V$ seen by a particle (for a 1 TeV proton must be 1 trillion volts), multiplied by the beam current $I$, gives you the beam power:
$ P = VI $. So in principle you may have some trade off between the two of them, but often there are other limitations both to $V$ and to $I$. The designs of most of the existing machines have stretched these limits as much as possible (either because of cost or physical/technological problems) so it will not be immediately possible trade $V$ for $I$ or vice versa.
For instance at the LHC the energy is limited by the maximum bending field that the magnets are capable to produce, so even accelerating a single proton, you wont be able to push it beyond the nominal energy (currently 6.5 TeV). On the other hand you cannot arbitrary increase the current as collective behaviours of the beams may lead to instabilities and beam losses. Moreover, due to field quality issues, the LHC cannot even accept particles at an energy lower than 450 GeV.
So basically the number of particle that an accelerator can accept is the design one. Most of the time, at an operating machine, it cannot be easily increased even giving up something else (a counter example is the fully-loaded linac of CTF3). During the design phase you can optimize it, but this may lead to completely different design! Have a look at the (experimental) fusion reactors: those are basically very-low energy and quality accelerators (they just need to overcome the Coulomb barrier and particles scatter everywhere) which however store a huge amount of particles. Their designs do not share much with the high energy accelerators.
Comment: Cannot accept lower than 450 GeV is a strong statement. Plans for a test injecting at 225 GeV are ongoing, as it would be an important part for FCC:
https://indico.cern.ch/event/662862/contributions/2712504/
Comment: @bjorn Yes, I was at that meeting, there are actually a couple of talks from myself :) However as things were (and still are today I believe), injecting below 450 GeV is not possible. Quite a lot of setup and MD time will be necessary to demonstrate a lower energy acceptance.
Comment: ah, so it won't happen before LS2 then I guess...?


What is the difference between "daemon" and "demon" in a religious context?

Question: Is there a difference between demon and daemon in a religious context?
Comment: "Daemon" is actually a much older form of "demon". Daemon is the Latin word for the Ancient Greek daimon. Originally in ancient religions daimons were lesser deities. Then Christianity came and "demonized" the other gods, so now you know them as the evil spirits from this mythology.
Answer: The OED writes that daemon is simply an alternate spelling for demon. However, Wikipedia writes that the two are subtly different:

The words daemon and daimon are Latinized spellings of the Greek δαίμων (daimôn), a reference to the daemons of Ancient Greek religion and mythology, Hellenistic religion and philosophy.[1] Daemons are good or benevolent "supernatural beings between mortals and gods, such as inferior divinities and ghosts of dead heroes" (see Plato's Symposium), and differ from the Judeo-Christian usage of demon, a malignant spirit that can seduce, afflict, or possess humans.

In this sense, a demon is solely a bad spirit. Daemons, on the other hand, are good. Note that the terms are from different religious backgrounds, and so they would not "coexist" in the same context. For most people, however, daemon is just a computer term. The only entry in the OED for daemon is:

A program (or part of a program), esp. within a Unix system, which runs in the background without intervention by the user, either continuously or only when automatically activated by a particular event or condition.
Comment: FWIW I've heard "daemon" used in a similar sense in some novels, for instance Philip Pullman.
Comment: *Daimon* is another word for *daemon*, I think.
Comment: In the programming context, "Daemon" is actually a cheeky acronym, standing for "disk and execution monitor". But to be honest, this is a backronym, only invented after the term daemon was already in use for background processes.
Answer: I've only seen the spelling "daemon" in the context of background services running on a computer to accomplish certain tasks without requiring direct user interaction.
"Demon" on the other hand means "evil spirit" to me.
Comment: What it means to you, personally, is – while interesting – not a very useful response for the question at hand; lacking context and sources – and it even does not actually directly answer the question.
Answer: In Plato's Phaedrus daemon is explained as a kind of good madness like falling in love, ecstacy, inspiration that takes the ego out of itself to a better self. Demon is a bad madness that is always self destructive.
Answer: Quite correct Raku,
You need to use the word as they were originally intended without Americanized, British or other pronunciations or colloquialism. Many groups of people try to phase out words to introduce slang or suite themselves and in so doing create a more illiterate society.
Daemon {day-mon}: Is a computer term for a background service and can in some religious myths be a "good demon" (There is also no such thing as a good demon as demon means to take control with evil intent)
Demon {dee-mon}: Derived Greek 'daimôn' Is a term given to an evil spirit that may interact with or manipulate the human spirit and its intent is to change or sway your understanding to what it wants you to do.
Comment: The 'originally intended' transliteration using the Roman alphabet is itself an example of 'American, British or other pronunciations or colloquialism'; the Romans did not mean exactly the same by the word as the Ancient Greeks did, and I dare say the Athenian understanding of the term was not the same as the Syracusan.  Language changes.
Comment: Not to mention that losing the a in _daemon_ is another one of those "pronunciations or colloquialisms", and the computer term in itself most definitely is. -1.


IED as abbreviation and term in Cyrillic/Russian

Question: With a new understanding of Russian, I found this is Half Life 2. I first started wondering why they decided to use Cyrillic to write "IED", and then I began wondering if there was an abbreviation (or even a term in the first place!) for improvised explosive devices in Russian. My dictionary did not lead me far. :( Can anybody confirm what the Russian version of the abbreviation and term IED is?
Comment: **Й** is not **I**.  _**Й** is  **Y**.   Russian language does not have words beginning with **Й**. Exceptions are geogaphic names (York, Yellowstone) and **йогурт** (yogurt). Accordingly, the Russian abbreviation cannot have **Й**.
Comment: The inscription is not valid: Д and Й are upside-down, but even if we assume the camera is upside-down and turn the image 180 deg, we get inverted (left-right) letter E, which is not a meaningful symbol.
Answer: The Russian Wikipedia article cross-linked with the English Wikipedia "Improvised Explosive Device" article via the "Languages" list is https://ru.wikipedia.org/wiki/Самодельное_взрывное_устройство or СВУ.
The letters in your image would have to be mirror-image flipped vertically to form valid Cyrillic letters, and then you get ДЕЙ, which doesn't mean anything in particular.


congruence for modular forms coefficients

Question: Let $A$ be the set of modular forms $f=\sum a(n)q^n$ of weight $k$ on $\Gamma_0(N)$ with character $\chi$ whose coefficients $a(n)$ are in the ring of integers $\mathcal{O}$ of a fixed number field $F$. Let $\mathfrak{P}$ be an ideal of $F$, Serre obtained the following result :
the set of primes $p\equiv 1\pmod{N\mathfrak{P}}$ such that $f|T_p\equiv 2f\pmod{\mathfrak{P}}$ for all $f$ in $A$ has positive density.
My question is about this congruence, taking two co-prime integers $a$ and $b$, is it possible to find infinitely many primes $p\equiv a\pmod{b}$ for which $f|T_p\equiv 2f\pmod{\mathfrak{P}}$ ? (we may replace 2 by other elements of $\mathcal{O}/\mathfrak{P}$).
Comment: It means that the Fourier cefficients of the two modular forms are two-by-two congruent modulo the  ideal considered. You can see the paper of J.P. Serre " congruences et formes modulaires".
Comment: If $f$ is a Hecke eigenform $T_p f = a(p) f$, it means that for any $\mathfrak{P}$ then $a(p) \equiv 2 \bmod \mathfrak{P}$ for infinitely many $p\equiv 1\pmod{N\mathfrak{P}}$ ? Why is it true ?
Comment: By using Chebotarev density theorem on the Galois representations associated to the modular form $f$ ! This is the beauty of modular forms !!
Answer: There are two questions, the one where you ask whether it is possible to find a $p$ in an arithmetic sequence s.t. $f|T_p \equiv 2 f$ and the one s.t. $f | T_p \equiv \alpha f$ for some $\alpha$ in the residue field.

Here I answer the first question, by the negative: no, it is not always possible.
Here is a counter-example: take $f=\Delta$, $\mathcal O=\mathbb Z$, $\mathfrak P = 3\mathbb Z$. Then as you say, by Serre's result, $f | T_p  \equiv 2 f$ for a positive density, and actually for all primes $p$ such that $p \equiv 1 \pmod{3}$. But $f|T_p \equiv 0$ for all primes $p$ such that $p \equiv -1 \pmod{3}$. To see both assertion below, since $f$ is an eigenform, it suffices to check that $\tau(p) \equiv 1 + p \pmod{3}$, which is actually a well-known congruence, where $\tau(n)$ is the $n$-th coefficient of $f=\Delta$.

Now I claim that the answer to the second question is also negative.
Here is a counter-example: take $f=\Delta^3$, $\mathcal O=\mathbb Z$, $\mathfrak P = 2\mathbb Z$. Then for all odd prime $p$, one has $T_p f \equiv 0$ or $T_p f \equiv \Delta$, but never $T_p f \equiv \alpha f$ for $\alpha \in \mathbb F_2$. Thus any $(a,b)$ gives a counter-example.

To give a positive result, let me say that the answer to the second question is positive when $f$ is an eigenform for almost all Hecke operators (or even infinitely many, that's enough.)


moving iMovie project to new Mac results in some sounds from same source missing

Question: I have two Macs, the first running iMovie 10.1.2 and the second running iMovie 10.1.8.  I completely copied the iMovie Library folder from the first machine to the second.  When I opened iMovie on the new machine it showed some progress in recognizing the new library, and then opened my project.  At first, everything looked fine, but then I noticed that some of the sound clips had no sound in them.  I see the green rectangle for the correct duration, but there is no waveform displayed in it, and when I play it there is no sound. When I reveal the source the original clip there is no sound there either.
It seems like roughly half of the sound is missing.  But the thing is, it's all from the same source file.  I compared the imported media file and it's identical to the original.   Furthermore, the sound is present in the actual media file.  I tried deleting the extra directories in the event directory (Analysis Files, CurrentVersion.imovieevent, and Render Files) and it was able to "repair" the event, but the sound is still missing.
How can I get my sound back?!
Edit: I enabled viewing the waveform in the event viewer, and it appears that the sound abruptly ends at 54.7 minutes.
Answer: Updating to iMovie version 10.1.11 (on the second machine, to which the project was transferred) fixed the issue for me.


Is there a way to decompress a Fody-Costura generated exe in c#?

Question: There is a program that is possibly a RAT, and I would like to view the source code.
After opening the .exe in dnSpy, I was able to tell that it was compressed with Fody-Costura. (https://github.com/Fody/Costura)
Is there any way to de-compress the file? If so, how?
Answer: Embedded assemblies needs to be decompressed before they can be used so you can inspect all the code that does that in the assembly. Just go to Costura.AssemblyLoader to check how it is done. below is a extract from a simple example using Costura.Fody.
Assembly executingAssembly = Assembly.GetExecutingAssembly();
if (fullName.EndsWith(".compressed"))
{
    using (Stream manifestResourceStream = executingAssembly.GetManifestResourceStream(fullName))
    {
        using (DeflateStream deflateStream = new DeflateStream(manifestResourceStream, CompressionMode.Decompress))
        {
            MemoryStream memoryStream = new MemoryStream();
            AssemblyLoader.CopyTo(deflateStream, memoryStream);
            memoryStream.Position = 0L;
            return memoryStream;
        }
    }
}

You could modify this code to save decompressed assemblies to disk by adding a line File.WriteAllBytes(fullName.Replace(".compressed", ""), memoryStream.ToArray()); or just extract dlls resources and decompress externally via python or anything else that can do deflate.
Comment: Hi! Thanks for the reply! How should I go about extracting the resources? I found a few resource extractors, but none of them seem to work.
Comment: dnSpy has an option to save reaources.
Answer: I had success using the Fody-Costura-Decompress tool.
You would need to build the solution from source. it has a simple GUI for choosing your file and decompressing it.


Java .class bytecode debugger

Question: What is the good Java debugger for .class files, if no source code available? jdb is seems pretty weak :(
I don't need to decompile .class, but I want to debug bytecode.
Answer:
Bytecode Visualizer
Inspect, understand and debug Java bytecode, no matter if you have the corresponding source.

JSwat Debugger
JSwat is a graphical Java debugger front-end, written to use the Java Platform Debugger Architecture and based on the NetBeans Platform. Its features include sophisticated breakpoints; colorized source code display with code navigator; movable display panels showing threads, call stack, visible variables, and loaded classes; command interface for more advanced features; and Java-like expression evaluation, including method invocation.

Java ByteCode Debugger (JBCD)
JBCD is an interactive debugger for Java bytecode. It allows a programmer to step through bytecode one statement at time. The tool is indended for people who are writing programs to generate or modify bytecode. JBCD can be used with any Java compiler

Bytecode Viewer
Bytecode Viewer is a Java Bytecode Viewer, GUI Procyon Java Decompiler, GUI CFR Java Decompiler, GUI FernFlower Java
  Decompiler, GUI Jar-Jar, Hex Viewer, Code Searcher, Debugger and more.
  It's written completely in Java, and it's open sourced.

JavaSnoop
A tool that lets you intercept methods, alter data and otherwise hack Java applications running on your computer.

Bytecode Outline
Bytecode Outline plugin shows disassembled bytecode of current java editor or class file, allows bytecode/ASMifier code compare for java/class files and shows ASMifier code for current bytecode. It also allows to disassemble and debug classes without attached source code on any operating system where Eclipse is running.

Addendum: This blog from Crowdstrike Inc. will also be helpful
Comment: Thanks for the blog link! I'll talk to our webmaster to see if he can fix the broken images.
Comment: Just a note to say that your first offering, Bytecode Visualizer, does not show you the stack or variable table, which is kind of a major limitation. I take it from your description that JSwat does, but that seems to be discontinued.
Answer: Possibly the best disassembler & assembler is Krakatau. It's written in python. Bytecode viewer has built-in Krakatau, but it sometimes can't perform as expected.
Another one is dirtyjoe which is also a great tool.

Java .class bytecode debugger


postgresql 9.1 failed insert occupies increasing disk space

Question: I have a postgresql 9.1 installation where the available disk space is very low (20Gb) however there is only one client that inserts data in various tables (typically one entry every few minutes) and a few web interface that show inserted data (refreshing every few minutes).
There is an error in the data reported of a specific table that generates a foreign key violation and overnight i find that all disk space is filled up; looking at the relation size i find that all the space is associated to a table and its primary key but no entries are present in that table (see FK error above).
If i reindex the pkey and vacuum table the space is correctly freed.
But i wonder, what is filling up space on error? is there a way to prevent that?
Answer: Error on inserting data due to FK constraint violation will leave dead tuple on the target table. That's the nature of Postgres. This dead tuple of course will occupy disk space. Things to prevent this filling up disk space :

A well tuned autovacuum can handle this wasted space.
Do a manual FK constraint check (on application side perhaps) prior to inserting data to the target tables.
Comment: thanks for you answer but that is a "normal" tuple or what? i.e. does it occupy more disk space than a successful insert? there's no way that if INSERTs were successful the occupied disk space would fill 20Gb overnight, we're talking of some thousands entry at most (with no blobs or free text fields)
Comment: it's a normal tuple but not visible, it's for supporting postgres mvcc http://www.postgresql.org/docs/current/static/mvcc-intro.html
it should occupy the same disk space as the normal successful insert, please note that it also increase index size. Is the 20 GB is the table and indexes size or PGDATA size? If it's the table size, i can't figure out why it occupy more than it should be.
Comment: I use the following query to stat the size of the relations: `SELECT nspname || '.' || relname AS "relation",
    pg_size_pretty(pg_relation_size(C.oid)) AS "size"
  FROM pg_class C
  LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
  WHERE nspname NOT IN ('pg_catalog', 'information_schema')
  ORDER BY pg_relation_size(C.oid) DESC
  LIMIT 10;`
Comment: Besides, i'll also add that i am monitoring the platform and since i last reclaimed disk space there have been a constant report of fk errors on that table but the table size is not increasing in a noticeable rate (let alone fill 20Gb in 8-12hrs or so). So, might it be something else?
Comment: Yes, that's the table size reported by the query. Then, there's definitely something else happened. It could be Your autovacuum busy on vacuuming another big table and let Your table-in-question unvacuumed and occupy more disk space. It could also be your autovacuum busy on freezing tuples http://www.postgresql.org/docs/current/static/routine-vacuuming.html


Extjs not working in google app engine

Question: I am trying to develop a google app engine application with spring and extjs in the view. I have successfully setup spring-mvc. It is very simple, I have a home view webapps/WEB-INF/views/home.jsp and I have mapped webapps/resources/ as /resources. I have copied Extjs-4.1 js library to webapps/resources/extjs. I know the mapping is working, as I am able to navigate to the resources, writing the full path in the address field.
My home.jsp is very simple, including ext-all-debug.js and ext-all.css in the header:

Extjs not working in google app engine


Where is the proper location to measure the tube size?

Question: I need to replace a tube in my bike. I know there are many tire sizes. I bought 26', assuming that my bike was that size, and realized when I got home that I didn't even know where to measure from. What is the correct location to measure in order to get the correct size of tubes?
Comment: Unless your bicycle is very special-purpose or old, by far the most common is 20 (bmx), 26 (mountan-bikes for example) and 700 (road bikes). Also, not only the wheel size, but also the WIDTH is necessary to choose the proper tube. Skinny tires need skinny tubes, and so on. By the way, did you have any problem with the tube you bought? Did it fit?
Answer: Look at the tire.  It will have the size embossed on the sidewall -- either inches diameter & width (like 26x1.5) or metric sizes (like 700C-32).  Use a tube that says it's for that size.
Tubes generally are made to fit a range of sizes.  Eg, a single tube may fit both 27" and 700C tires, and 1.25-1.5 inches or 32-38 mm wide.
Answer: If you still have the old tire, then the easiest method is to check the markings on the tire. But if you don't, then you have to measure the rim's bead seat diameter (see illustration). Here are the most common sizes:

622 mm : 700c, or 29 inch. Common on road bikes and some mountain bikes.
630 mm : 27 inch. Used to be common on road bikes, now obsolete.
559 mm : 26 inch. Most mountain bikes, some hybrids.

Source: Sheldon Brown. See his article for more obscure sizes, and an explanation of what it all means.
Comment: Note that tubes are interchangeable between 700c and 27". Tires don't stretch, so you need the exact diameter; tubes stretch quite a bit, so you have a margin of error of at least a few millimeters.
Answer: As a side note tires sizes on older bikes were not standardized.Not all 26inch tires from different bike makers will interchange. A 26x13/8" will not interchange with a 26x1.90 tire, the tubes however will.Always reference the size on the side wall of the tire rather than trying to measure the wheel diameter.


How to play faster songs on the violin?

Question: I am a student who is currently in middle school and have been taking orchestra classes. For the 4th year we're required to play very fast songs; so I am to slow to play the music and when I get to the tricky sixteenth note I can't even play the right notes because it's going so fast. Does anyone have some suggestions I would prefer not having to buy things to help me get faster and read notes faster?
Comment: loosen the fingers! stiff fingers is the natural reaction, but they won't help at all.
Answer: TL;DR;
Practicing in itself will get you faster for a time, and will max out some day. You need to get your overall play to become better, finer, by practicing in stop motion, removing any unnecessary movement from your play

In direct contradiction to everyone here, the key to playing faster is not to practice, even though you will get faster by practicing the right way.
Keep in mind that I'm not speaking about raising up your metronome forever and getting your fingers to play very fast. I'm speaking about speed in thinking and executing, and the key to get those is not to practice for the sake of practicing.
The key to playing faster is to clear your mind while playing lots of notes
To achieve this, you have to stop thinking about individual notes, and start thinking about beats, measures, or sentences. If you see an e minor scale ranging on two bars, you can play it very fast by practicing hours with a metronome while slowly raising the tempo, or, get your mind to actually execute two distinct bars of E minor scale.
Using the former way, you will be playing fast, but your mind will be used up thinking about what's happening with your hands, and you will probably stop thinking about anything else (which is a huge problem if you intend to play in serious ensembles).
Using the latter way, you will not only play as fast, your mind will also be clear, letting you play fast with the other people in your ensemble. Even when playing alone, having place in your mind to think lets you play more sensible music, as you can add some spices to make it better.
Considering notes as beats, bars or even sentences
The actual practice of playing faster is not at all intuitive. The best way I've experienced (best meaning achieving better or similar results while practicing less time) is to deconstruct your movements to their smaller components, and stop your movements between each of them (stop-motion).
That means stop between each bow. Completely stop, don't move anything. Then, think about where your fingers are actually, visualize where they need to be for the next note to be played. If you have a string change to make, think about what it will be. Then, when you have visualized all this, you can execute the change, as fast as you can, that is move your fingers and your bow together to their next position, without yet playing the note.
Then, play your bow stroke as you would normally do. If you're not in tune, start over.
You don't need to do that for hours at a time, as at the start it is very tiring mentally. Even 15 minutes of stop motion practicing a day will get your play to be a lot better in as small as weeks by defining the sound, and clarifying your mind, giving you greater pleasure while playing faster and with less noise in your sound.
Answer: What you really need to become faster is simply:
Practice
A virtuoso will have practiced for tens of thousands of hours, practicing their accuracy, finger speed, odd intervals, runs, trills and arpeggios.
There is no short cut. Just practice.
I would suggest buying a metronome, as it will really help you improve speed and accuracy over time, so you can try a particular passage at, say 140bmp, then raise it to 150 until you can comfortably play it, and increase again. This has the added benefit of helping you know at what speed you can consistently play - providing good milestones.
Comment: Just to add: if you want to play fast, you must practice slow. The passages must be perfect and slow. Once they are perfect, you can gradually stagger-increase the tempo to a pace beyond your target tempo. This will ensure you are able to perform the passage at performance speed. Practice with mistakes is learning poor technique and habits.
Answer: Of course, the answer is to practice. But  simply playing the same thing over and over again at different speeds won't necessarily be effective.
Try playing variations of the difficult runs. In particular, try it with different rhythms. (For example, change a run of 16th notes into dotted rhythms — LONG-short, LONG-short, etc. Then reverse it as short-LONG, short-LONG, etc.). Also try it with different bowings. The idea is to get your left hand to be able to hit every single note, and the varying emphasis will force you to play the weak notes too.
Answer: As everyone else has already answered the answer is ... practice. Here are three practice techniques and a performance technique that I've found useful.
Metronome
Find the metronome beat at which you can play the passage comfortably. Play it through a few times at this comfortable speed and then notch the metronome up. Keep mastering the passage at each new speed so that you can play the passage through twice without error before moving on. In each practice session start off slow and build up. (N.B. This works really well and is super rewarding but is a nightmare for others in your home as they are subjected to the same short phrase over and over and over again which is like torture for them. Choose somewhere out of earshot to practise this way!)
Hard Notes
You mention that you "can't even play the right notes". If it's the notes that are blocking your speed try messing with them. Play them backwards, play alternate notes, play them as chords, etc. etc. Do whatever you can to really get inside the phrase. Sometimes doing something that makes the phrase harder will mean that when you return to the original it now feels easy!
Go Insanely Fast
Sometimes we do not know what we know. I have had moments in orchestra when, in performance, we have hit a passage that I know I cannot play and yet my fingers have just ignored me and played it anyway. The fear and excitement of playing far beyond the speed one's conscious mind can deal with is another way to learn.
The Notes are Only a Guide
You mention that this is for orchestra classes. In practice and in class you need to try to get the notes right and at the right speed. But in rehearsal and (dare I say it) in performance you don't. As long as your playing is not making the orchestra sound worse you are alright. If it is a dire passage you cannot get on top of at all then just mime. I sometimes joke with my family that they will be able to tell when I'm miming as my bow will be in sync' with the rest of the section! Better than miming is to find which notes you can leave out. If the conductor sees the section's struggling she or he may suggest that to you, but often you can tell which are the important notes of a phrase (e.g. the first in each bar). Just play the important notes.
Comment: Well, I hope people won't take your "cheating advice" all too literally and apply it in inappropriate places... but yeah, I'd confirm most of what you say; in the orchestra there are other rules for what'll sound good than when you're playing alone.
Comment: @leftaroundabout that last phrase of yours: "in the orchestra there are other rules for what'll sound good than when you're playing alone" is a great way to put it
Answer: Uh, practice.  Learn your lines by heart.  Sight reading is nice and useful, but it's a secondary skill.  At high speed, it consumes a lot of your focus.
And frequently practice at half speed or slower, nicely detaching and properly phrasing your notes.  At a speed where you can listen to what you are doing and not have your focus consumed by just blasting stuff out.
That's the realistic way to figure out where the weaknesses in your fast play will be which eventually will brake you down.
And of course, ask your teacher.  Fast playing demands a lot of relaxation and suppleness in hands, wrists (yes, both), arms and shoulders.  Without someone pointing out the weak points and/or developing exercises against them, you are likely not to work where it counts.
Answer: Two major things I'll mention which I consciously practice while learning a fast passage:
Keep your fingers down! It's very easy to develop the bad habit of flapping your fingers around like mad as you race over the notes.
You should aim to be hovering all fingers barely above the string and absolutely minimize the amount of finger movement required to play the passage.
I find this easier to achieve by focusing on my 4th finger and the others follow suit, it will also help to rotate your left elbow further to the right so your hand is more 'over' the fingerboard (this will take some getting use to).
Secondly swing the rhythm of what you are learning, (works best for runs of even valued notes).
For example If you're playing a run of consecutive quavers, first practice as dotted quaver followed by semi-quaver until you get up to speed, then reverse the rhythm (semi quaver followed by dotted quaver).
Answer: That is a great question, and a very common problem.  I was just recently addressing this problem in the practice room. I wanted to get to play certain parts of the Williams/Stern cadenza from "Fiddler on the Roof." It took me a little while to work up to -this takes time, but I've observed the following to help, considerably.
Make sure you know what you are listening for
Break the passage up into chunks, measure by measure (or smaller, if convenient).  Play each note slowly, with long bows, and make sure that each is tuned well.
Variate the Rhythm
Break the passage up into chunks by measure, again. It doesn't really matter what the original rhythm is, this process just teaches your fingers how to play each note quickly, one at a time. Take your time. First, play every other note as fast as you can. What I mean is that you would wind up with something like a dotted-eigth-sixteenth-note rhythm, but not precisely. That second note is played just as fast as your fingers can manage (while still being in tune and clearly sounded). Once you are comfortable with that, switch it. Play the first note quickly, and then every other. Once you are comfortable, move on to groupings. Play one note slowly, and the next two notes quickly. Once you are comfortable with that, play the first note slowly, and the next three notes quickly. Switch up which note is the slow one, and which ones are fast. This is a long process, but it works very well.
Accelerated metronome
After you are done with the above, take the metronome and put it on a slow setting. It should be so excruciatingly slow that you can't help but play it right. After that, take a moment to reflect, and bump the metronome up by 5bpm. Continue doing this until you reach the target speed.
Examine finger pressure
Even after I have done the above, sometimes I still get thrown off by excess pressure in the left hand. Nathan Cole posted a great exercise on his channel. I use this myself and am going to start introducing my students to it.

That being said, it may take a couple of days of using this, even a week, to feel really very comfortable. However! Keep at it! It will come!
Let me know if this helps!
Comment: That is a great answer and video, thanks a lot I had never heard of Nathan Cole and I'll be sure to check those videos more.
Comment: I'm glad that my answer was able to help, @Felix. Yes, I only discovered Mr. Cole's channel, recently.  His teaching style is very down-to-earth and kind, while still being critical. He reminds me of one of my former teachers. Good videos, for sure.
Answer: There is a widely regarded book for pianists
http://www.pianopractice.org/book.pdf
I guess much of it will not directly apply to other instruments like violin
However some of it is generic ie will apply to all kinds of practice eg see pg 127 fast and slow muscles
Answer: Ok I had the exact same situation (I'm in level 4 too) and I found the answer. A metronome (or a metronome app is what I use) and patience. So the metronome came in handy for me because I was rushing and it became sloppy. With it I could slow down. The patience part is what came hard because I am pretty impatient (part of the reason I was rushing and needed a metronome in the first place). But now I'm starting everything very slowly even though I want to go faster. I've been improving way faster than before I used the metronome. (If I would have done this earlier I'd probably be in level 7 if that even exists)
Answer: In addition to the great answers ioseph and 200_success gave:
First, make sure you have good fingerings.  It might be a good idea to get some help on this (private teacher, school orchestra teacher, more advanced student, etc.).
Practice small groups of notes and make sure you are grouping the notes, and playing in a very relaxed, comfortable way.  You'll probably want to start with five notes at a time.  To explain how to do this, I will number the notes in a 4/4 measure from 1 to 16.  First, play notes 1 through 5, allowing yourself to give notes 1 and 5 a natural stress.  Then play notes 5 through 9, and so on.  You'll allow one whole beat for the first four notes, and another whole beat for note # 5.  Allow your arm to hang more heavily on notes 1 and 5; and then in the second group, on notes 5 and 9; and so on.
A great way to make sure your hand is relaxed is to vibrate each fingered note.  If you have a nice sounding relaxed vibrato, you won't be able to seize up (get tense) while playing with vibrato.
After a few days of practicing like this, you can proceed to groups of 8 notes.  You'll play notes 1 - 9, and then 9 - 17.  (17 = the first note of the next measure.)
Please don't try to speed up before you're really, really ready.
Realistically speaking -- there comes at least one time in every string player's life when there is no solution other than faking it.
Answer: I think I finally figured out a good way to play the fast parts! First just put your bow away and finger through the fast part, a few measures at a time, and try to memorize the notes. Basically, program the fingerings into your left hand so you won't have to worry about that part while you're playing (sounds weird, but it works!) Then, after your fingers can confidently move through it, try adding in the bow. If you have issues with coordinating your left and right hand, try playing it slowly to make sure both your bow and your fingers are in sync, then gradually speed up. I'm not that experienced (this is my fourth year too), but this method worked really well for me, so I would totally recommend trying it!

How to play faster songs on the violin?


How to determine a quantization table for image compression with DCT?

Question: The quantization table is given on the JPEG Wiki page. How was this table derived? I'm currently doing a project where I have to come up with custom quantization table for an image, but I don't know how to begin. I figure if I learn how the JPEG table was derived, I might come up with a semi-original idea.
Answer: The standard JPEG quantization table is a actually an 8 x 8 matrix of weights whose elements divide the corresponding elements of the 2D-DCT coefficient matrix of an 8 x 8 image block.
The division effectively reduces the magnitude of the DCT coefficients and most of them are forced to be zero, due to the integer divison rounding.
The standard table is determined to yield a minimum distortion under maximum compression applied to the most typical image (i.e., exhaustive average of large image data set) and typical viewer visual characteristics.
As a result of this quantization, high frequency coefficients are reduced as much as possible.
Note that the JPEG quality parameter provides a means of scaling the standard quantization table weights, but no control over individual elements.
You can also design and use a specific quantization table for your needs, according to the rate-distortion criteria you have in your mind. But this requires you to embed Q table information within the compressed data bitstream.
Comment: Is is possible to optimize the quantization table to the whole image. It will cause the overhead of storing the quantization table on the header, but I usually leads to good results. That is the approach done by the JPEG encoder Guetzli created by Google. See: https://github.com/google/guetzli/
Comment: could I somehow perform an analysis of the 8x8 DCT coefficients so I can see which pixels in any 8x8 block exhibit the most variance and then create a quantization table based on the calculated variance?
Comment: yes (probably) you could something similar. But then you should also **embed** that specific  quantization table into the JPEG bit stream and hence lose the very means of compression refficiency...
Comment: @LEo yes you can design a whole image optimized quantization table and transmit this (or embed) with the compressed picture data.


Trashing Market Square and another card at the same time

Question: I use a card that allows me to trash 2 cards from my hand (like Chapel).  I trash Market Square and another card.  Are the cards trashed simultaneously or sequentially?  Does either possibility allow me to use Market Square's effect?  If so, where does the Market Square end up?
Answer: The cards are trashed at the same time, so if you are trashing Market Square, you would not be allowed to discard Market Square for its effect also.

You choose all the cards you want to trash, and then trash them at the same time; you don't trash them one-by-one. This matters for interactions with Dark Ages cards with on-trash abilities.

Dominion Strategy Wiki
Also, from the Dark Ages rulebook:

When two or more cards are trashed at the same time, as with Count, first trash them all, then pick an order to resolve things that happen due to trashing them.
Comment: The rules in Alchemy specifically state that when discarding cards from play, cards can be cleaned up in any order. With actions such as Cellar and Warehouse, which have you discard multiple cards, cards are discarded at the same time (though of course they need to end up in some order in the discard pile. But your opponent's don't get to see every card you discarded, only the one that ends up on top).
Comment: While I'm not disputing this ruling, it does seem to go against how Alchemist is handled: you can discard your played cards in the cleanup step in whatever order you choose, allowing you to get your Alchemist back before discarding your potion.  Is trashing the only game action where multiple instances happen simultaneously?  How does that work?
Comment: @codebreaker To add to what Gendolkari said, the rules in Dark Ages specifically state "When two or more cards are trashed at the same time, as with Count, first trash them all, then pick an order to resolve things that happen due to trashing them."  However, Market Square has to be in your hand to be used as a Reaction, but your Chapel already put it in the trash.  Besides which, even if you could do them one by one, by discarding Market Square, it's no longer in your hand to trash.
Comment: @Powerlord, thanks for that; I edited it into the response.
Comment: Thanks, didn't know that about the cleanup step working like that.  Just out of curiosity, when you gain multiple cards (like from Develop, Thief, and Beggar, for example), does that happen all at once?  Or does the simultaneous thing only apply to discarding/ trashing?

If you had Watchtower out and the gains happened simultaneously, wouldn't that cause Watchtower to lose track of all but one of them?
Comment: I believe Donald X. clarified at one point that gains have to happen one at a time.
Answer: You can't gain a gold by trashing Market Square, only by discarding it.  Once you've trashed it you can't then discard it.  Consequently you can't gain a gold by using Chapel to trash it and another card.
The only way I can see to trash the Market Square and use its ability is by discarding it, reshuffling, picking it up again and then trashing it.  This could be done using the Doctor with a bit of luck (or a very small deck):

Play a Gold and a Silver
Buy a Doctor for 5 (overpaying by 2)
Pick up the only card in your deck and trash it (Doctor overpay ability 1)
Discard Market Square from your hand and gain a Gold
Shuffle your discard pile and place as a new deck
Draw the top card (which turns out to be the same Market Square) and trash it (Doctor overpay ability 2)


How do I rewire LED security light to bypass motion detector - without burning out solid state board

Question: I purchased a deluxe motion activated light for my porch.  I assumed that there would be an override feature to bypass the motion sensor for manual operation; after a few days and nights of various trials with switching on-off patterns, I resorted the manufacturer's help line. Unfortunately, the answer was, "If it is not in the instruction manual, then it is not an available feature." And I was further advised not to attempt to bypass the motion detector, or I would burn out the circuitry.
Please, is there something I can do/modify to set this into a manual mode? I do want the photocell to continue to control dusk-to-dawn, just constant on throughout the night, unless I choose to return to motion detector operation (not a necessary option). I do want to keep this on a switched circuit (single fixture control). I can remove the motion sensor entirely if that is the most appropriate means.
I have not seen this simpler feature available in the deluxe, ultra bright twin light system (yet, anyway) otherwise I would have simply purchased a new light. I do have smaller, single outdoor LED lamps, but not the double lamp with it's broad illumination.
Thank you for any help.
Comment: There's not much to go on in your question.  Can you post the manufacturer and model info? Also a photo of the circuit board may help.
Comment: If you're really paranoid, you can use a 3-way switch with one traveler going directly to the LED and the other going through the motion sensor first before going to the LED. This way there's no power going to the line side of the motion sensor when it's being bypassed. No idea if or how any of this would impact the circuitry.
Comment: If you are saying that you just want to be able to switch it on and off manually, I think you should be able to figure out whether that's doable. Try to find out what type of voltage and the number of volts being used by the LEDs. If they are 120 volt AC, then you just have to connect the incoming power directly to the LEDs and bypass the circuit board. BUT, I've never done this. This is just what I would try.
Answer: I've done this.   I have a great solution.
Simply take the hot circuit to the sensor and to the light switch and run them in parallel.   The only downfall is that you won't be able to turn the light off when the sensor has control.  But I haven't found this to be a problem.
Answer: All motion detectors have an override mode. Typically this is done by either flipping the wall switch off/on in a certain pattern, or by a switch on the motion head.
Thing is, when you put it in override mode every one I have seen reverts back to motion after the next night/day cycle. I have NEVER seen a motion detector that has a permanent manual override mode.
Comment: I don't know whether it's "all", but certainly it's "most". I'm not sure whether mine reverts after a day or not; I've never had it turned off that long and reverting would actually be what I'd want it to do so I have no reason to investigate.
Comment: I've never seen a motion detector without one of some sort or another.
Comment: I'm agreeing, just recognizing that "never seen" doesn't imply "doesn't exist." All it takes is one counterexample. And I've seen motion detectors separate from light fixtures which may not have that feature built into them.
Answer: When there's a TEST switch position in a typical motion light, putting the switch to TEST turns the light on. Then just turn off the switch in the house. Whether this would work in a dusk-to-dawn light, I don't know. Hope this helps.
Comment: It won't, motion sensors do not like being downstream of switches because they need power to remember what day vs. night looks like *in this location*.  If you switch them off they fall back on defaults, which performs poorly in many locations.
Comment: A test switch or function on a motion detector does not simply turn the light on. It puts it into a state where it works off motion but only stays on for approx 30 seconds at a time.


Is there a way to use less specific Twitter location?

Question: I'm not sure if this would be a setting on my Android phone's Twitter application or on the Twitter website, but I want my tweets to have a location, but not my fine-grained location. Preferably, just identifying the town or city where I'm located, but anything less granular than my exact GPS coordinates to what appears to be a 30 foot accuracy would be fantastic.
Answer: When using mobile.twitter.com from any mobile safari (on iOS devices) you can choose to use your exact location, or just the location of your nearest neighborhood.
If your twitter client does not support this, try using the browser on your device.
Comment: That'll do for now, and addresses my issue for this question. Now, I'm going to go off and keep looking for a way to do this with the official Twitter Android client.


Is there a study that has been done showing the transformational power of the Holy Spirit in people's lives?

Question: It's pretty clear that the Bible promises to change people's lives. It's also pretty clear that it did significantly change people's lives such as the apostles and others both in the the present day (e.g. Chuck Colson) and throughout history. My question is, has there ever been a study done to show the transformational power Christianity has in a person's life? It seems like a study such as that would provide significant evidence to support the claims of Christianity.
Comment: Welcome! Thanks for contributing. This is an interesting question, but you could make it more clear by specifying what kind of *transformation* you mean.  Obviously no study can measure the condition of the heart, so we are left with external behaviors.  Criminal recidivism rates? Hours of volunteer service? Hopefully you see how difficult it would be to quantify this.  If you haven't already done so, I hope you'll take a minute to take the [tour] and learn [how this site is different from others](http://meta.christianity.stackexchange.com/a/1809/21576).
Comment: The Bible tells us that "by their fruits you shall know them" (Matthew 7:16). Therefore, we should expect to find people who were producing wicked fruit before they were saved, and the fruit of the Spirit afterward. Therefore, criminal recidivism rates among among criminals who have gotten saved vs those who have not works probably be a good start.
Answer: The simple answer to your question is yes, there are many such studies, and here is a good place to start looking for them:
The Nature of Spiritual Transformation - A Review of the Literature, Prepared byArthur J. Schwartz, Ed.D.


Should I back up the private key from the metamask wallet

Question:
Where metamask store privatekey? are they stored locally or remote?
How does metamask protect my privatekey? I assume that they are somehow encrypted by the seed phrase?
How does metamask restore/import my wallet (using the seed phrase)?
if the privatekey store locally then how does it work when using new computer?
if it is stored remote, what measure are taken to secure and keep the data availble?
should I back up the private key from the metamask wallet, or does the seed phrase is enough to secure the coins at any circumstance?
Answer: Your private key is stored in your browser.
Metamask ask you for a password to encrypt the private key.
No it's stored locally.
Always back up your private key. It's better to store your "mnemonic phrase" as they are human readable. A naked private key is hard to copy, and any error (a character change) can be lethal for your back up because you can't see the error.
https://metamask.zendesk.com/hc/en-us/articles/360036464651-How-to-Recover-a-Seed-Phrase-Secret-Recovery-Phrase
Answer: I login to metamask from a different PC with the seed phrase only and verified that the private key are the same, thus metamask back the private key on remote server (probably encrypted by the seed phrase)
BUT reddit users complains that sometime the import process fails therefore it is important to backup the private key as well!


How to prevent discoloration or parts in storage?

Question: I recently moved into a 1 bedroom apartment, and I am storing my Lego sets out in the living area. There is one problem: one wall is practically all window. Since it is unrealistic to have the blinds closed all of the time (since the lighting isn't great), and I don't have the space or money to buy display cabinets with the special glass that filters UV light, I installed UV film to the windows.
Will this be enough to save my Lego sets from suffering from discoloration, or should I be doing something else? This situation is only for a year or two, then I hope to buy a house where my sets can safely live in the basement, away from sunlight.
Answer: Product description says:

UV protection helps reduce fading on flooring, furniture, portraits, blinds and draperies

Reduce, not eliminate, because such film cannot remove 100% of UV, and regular light can also participate in fading a bit.
If you want to store them, not to display them, then box will do. One that isn't transparent. There are opinions that airtight boxes help, too, but I haven't tested that. Regular dark box did a pretty ok (not perfect) job for me when I stored my bricks for many years.
Comment: I want to have them on display, has anyone (Lego or someone independent of Lego) measured how long it takes before white starts to turn yellow/tan?  I have never had my bricks turn this color, but I have inherited some sets with white bricks that are so discolored they almost match the light tan bricks.
Comment: @Jedi_Maseter_Sam measurement is impossible - exact recipe for LEGO plastic was changed a few times, so any long term results had to be outdated. Modern recipe is supposed to be rather resistant to color changes. Also, it depends where on Earth you are, on what side are your windows, is ozone layer good where you live and so on.


Looking for a starter kit for my 10 year old

Question: My daughter would like to get involved with computers.  I have heard that a Raspberry Pi is a good place to start.  Her mother and I think that she would like to create a motion sensor camera so she can put it outside of the bird house she made.  I found a couple of kits online, but since I don't have any idea what I am doing I thought I would give it a shot and ask for some help.
Comment: To be honest, if she wants to get into computing you don't need a raspberry pi (which is over hyped and the ARM hardware induces additional complexity). Just pick up an old computer and let her install Linux and play around with it.
Comment: @AndréBorie I was a little torn about answering this because, as I say at the end, I think things may get a little frustrating for a ten year (there are certainly plenty of adults that show up here expressing such).  But OTOH, learning via a Pi may grab a kid's interest more than simply plunking down a laptop with a bash and python tutorial.  It's a gamble.   If the parents are not already linux users, then they will probably have to be prepared to sit up a few nights, lol.
Comment: Completely agree with @AndréBorie. There's this bizarre notion lately that people can't get started programming with *normal* computers. Just get an old laptop or something - comes with everything you need and is portable too.
Comment: AFAIK you can make snapshots with motion detection with the standard raspberry pi camera tool. So you will just need the pi with the basics (PSU, maybe a case, maybe wlan adapter) and the camera.
Comment: Thanks everyone for the help.  This is a lot to think about.  My wife and I will discuss where to go from here.  We appreciate all the time and effort everyone put it.
Answer: There are a few things in addition to the pi itself that are required, and if you do not already have them, you would want a kit that includes them.  Generally these are appropriately priced, but depending on what is available to you it may also be easier to buy them separately:

Micro SD card. You can get these with an operating system pre-burned, but do not pay substantially more for the convenience.  The OS is free anyway, and it is not difficult to copy an image onto a card -- also, this is probably something you should get comfortable doing as sometimes the quickest solution after having screwed something substantial up is to just start again from scratch.
You want at least a 4 GB card and preferably 8 or 16, especially if you intend to take a lot of photographs or video on the card.
Power supply. 5V, 2-2.5A DC with a microUSB connector. Many devices (e.g., Android tablets) come with these, and supplies with slightly higher voltage are becoming increasing commonplace; this is probably a good thing but do not exceed 5.25V.  Not all power supplies are created equal, and ones that are intended for charging may be marginal in the sense of not living up to their ratings; another culprit here are substandard cables, but this is not a difficult problem to solve.
If you can't run an extension cord to the birdhouse, the pi can be run from a 5V power bank, but it is not as efficient as (e.g.) smartphones.  A 10,000 mAh battery should be good for at least 4-6 hours (depending on the quality of the battery, it may last much more1), but beware in this scenario that letting the pi die from lack of power is not a good habit to get into.  It will not cause physical damage, but it can cause filesystem corruption (a potential "start again from scratch" scenario).
A 15-20W+ solar panel with 5V, 2A output is also a feasible power supply if you can be certain it is going to receive a good dose of sunlight, otherwise it will cut out on you.
Case. This can be improvised, and the board does have mounting holes, but considering there are many cases around for $5 or less, it is a good idea to get one built for the purpose. If you are going to use the CSI camera connector (e.g., the official Pi camera), make sure the case has a slot on top for the cable.
Wifi Adapter. The Pi 3 is the only model that has built in wifi, so if you are going to communicate using a different model in a birdhouse you'll probably want one (also, it is more generally convenient than an ethernet cable).  Most cheap ($10-20), widely available adapters should be fine, but beware that manufacturers do not produce drivers for the pi, so this is dependent on one having been created by a third party. The linux kernel, which you will most likely be using, has this reasonably well covered, but there are still plenty of adapters around that can be troublesome.  If you buy one as part of a kit, it is (hopefully) a safe bet.  Otherwise I recommend getting one from a local store where it is easy to return something undamaged within a short period if it turns out not to work for your purposes.

I think you are best off with a quad core model (i.e., the Pi 2 or 3, aka. "2 B" and "3 B" but there are no other 2/3 versions so the "B" is superfluous).  Other basic accessories useful in setting up and working with the pi are a USB keyboard, mouse, and HDMI cable for attachment to a monitor or TV.
With regard to the camera, you can use commonplace USB webcams but these can also be a gamble with regard to driver support; the official pi cameras (5 or 8 MP; beware there is a "no-ir" version which you do not want) are the best bet.  The down side to these are 1) They require a special cable; generally they are sold with one 6-8" long but they are available in lengths  up to 24", and 2) They are very small, delicate, and like the pi do not include an enclosure.  There are cases available for them and they also have (very small) mounting holes.  It is not particularly difficult to attach the camera inside a tupperware container with room for the pi itself, although you will want to drill a small (~1/4") hole for the lens.
I've done the above and covered the hole with a very thin layer of clear plastic (e.g, from some kind of packaging) epoxied onto the outside of the tupperware; this is fine since the camera does not autofocus, and if you compartmentalize the container with some bits of cardboard, styrofoam, etc., and use decent quality locking style tupperware, you can squeeze a pi with camera and powerbank into a fairly weatherproof, 10" x 6" x 2" box.  If you are using this outside in the heat be sure to monitor the CPU temperature (there is a built-in sensor) via wifi; it is unlikely to be a problem, but the power banks generate additional heat and combining that with direct summer sun and no ventilation may not be a good idea.
Something else to consider...

My 10 yr old daughter.

I think this is a very minimal age for a project like this, depending of course on how tech savvy her parents are ;) I did teach myself BASIC on a VIC 20 at only a year or so older than that, but beware this is something that will take a lot of patience and probably involve a lot of frustration.  A pi is substantially more complicated to use than a VIC 20.
In case my point isn't clear, beware you will not have a birdhouse cam at the end of the weekend kind of thing.
Of course, sometimes you don't need to actually catch the carrot on a stick in order to have fun and learn some things.  I would emphasize the journey and not the goal.

1. The reason I've used 10 Ah as an example here is in general, if you want to do things this way and are shopping for a new battery, I do not think it is worthwhile buying anything smaller although in theory such a battery could last 20-40 hours (see discussion in comments below).  I have not done a lot of research and experimentation this way, but I suspect a problem with many/most power banks is that as they run out of power, their voltage starts to fluctuate; this is fine if they are used for what they are mostly advertised for use as -- charging.  However, with a pi, if the voltage dips below a certain point, it will stop working, and this may happen long before the battery is actually dry.  Put another way: "Your mileage may vary".
Comment: Very well put, Goldilocks, as always
Comment: I agree this is a good answer, but a 10000mAh will last days. The 2A spec for the Pi refers to the peak consumption, an headless application with no mouse or keyboard requires less than a tenth of that.
Comment: @VladimirCravero You're right, it might, and that is a very conservative estimate (I'll add a reference to these comments).  However, keep in mind that not all power banks are created equal -- I think they are notorious for using idealized ratings.   The tupperware box I used was a few years ago, with a model B and a (debatable quality) 8000 mAh battery; that would last 3-4 hours (probably voltage drop as it ran out of juice) but of course, it also depends much on what you are doing.  I did not have a USB ammeter then, but now I do I'll add a few observations:
Comment: That same B idling uses about the same current as my Pi 2 does while streaming half size, 30 fps video (~8 MB/s) -- 3-400 mA.  However, that's *over ethernet*.  Add a wifi adapter and I think you will be up over 500 mA.  So a very liberal estimate would be 20 hours.   Of course, if you are using `motion` or something, you won't need to be streaming video constantly, etc.
Comment: Anyway,  the reason I said that about the battery is I do not think it is worthwhile trying this with anything smaller (unless you already own one, in which case you might as well); i.e., I did not want to recommend someone buy a 4000 mAh battery on the premise that it will last all afternoon because I am not so sure that will be true, and you might as well err on the conservative side WRT to this choice.
Comment: Put another way: There are a lot of options here and once you are satisfied everything works the way you want you don't actually need any communication, you could make a decision about the battery and how long to leave it in the wild etc.  I did not want to end up turning every paragraph into a chapter in a book ;)


Mind blowing issue on my hands ✋ pedal goes to the fl

Question: I have a 2003 Chevy suburban. I'm stumped On this issue with the brakes, now when I 1st encountered this I replaced brake lines Just 2 That were busted Then bled the system Just find out master cylinder was bad Replace the master cylinder twice blend system again Still pedal goes to the floor,bled system number of time manually and with the machine still pedal goes to the floor then replaced the 2 rear rubber hoses bled the brakes again,now here's where it gets weird pedal is spongy but it holds for the day then let it sit over night back to the floor just replaced the brake booster still no fix if anyone can help let me know
Comment: Can you please edit that **wall of words** into digestible  sentences and paragraphs with proper punctuation.
Answer: Welcome to MVM & Repair!
The problem you're experiencing is caused by one of three things:

Brake pads are missing, brake disks are missing or brakes shoes (inside the brake drums) are not adjusted properly. Make sure the brake pads are in the right place and that there's not a huge hap between the pad's surface and the brake disk. If the rear brakes are drums, make sure the brake shoes are adjusted properly. You can test this very easily by pulling up the hand brake. If you feel no resistance, adjust the shoes, by taking off the drum and turning the self-adjuster.
There is air in the system. Pretty straight-forward. Bleed the brakes (preferibly starting with the brake that is the furthest from the master cylinder, which will be the rear right on left hand drive vehicles). Loosen the bleed nipple, slowly press the brake, tighten the nipple, release the brake, repeat. Make sure there is sufficient fluid in the resevoir.
There is a leak in the system or a bleed nipple is not tightened properly.  Replace the part that's leaking and bleed the brakes until there's no air in the system.
Answer: Sounds to me like you have air seeping into the hydraulic lines overnight you should check every fitting maticulously don't try and rush brake jobs, have you checked all cylinders for leaks and does the car have abs if yes it needs special bleeding via computor to flush the pump.
Comment: I have checked for leaks and there is none, I don't know what you mean by cylinders cuz I have disc brakes all around
Answer: In conjunction with the previous answers, you may need to bleed the ABS system. This is usually done with a scan tool.
Comment: Did that about 3 time during the bleeding process
Comment: If there are no leaks, there is air or leaking seals. There are cylinders on disc brake systems in the calipers. With a small screwdriver pull the rubber seal around the piston out a little all the way around the cylinder. If you see moisture, you have a leak. Also be sure to bench bleed the master cylinder. Of there are no leaks anywhere including the cylinders and there is no air anywhere in the system you probably have a bad or wrong master  cylinder.
Answer: Check
Rubber(connects on shock column) and Steel(long feed goes under car) brake lines
Proportioning valve
Caliper pistons seals
ABS modulator
Answer: How to check :

Check if there is anything missing.
Check if the adjuster at a good position on your brake booster (the new one usually have a slight difference)
Bleed the master cylinder.
Bleed the brake from all tires.

The most overlooked is to bleed the master cylinder because everyone just focuses on the tire.
How to bleed your brakes instruction can be found here:

Dummies.com
Youtube.com

And don't forget to tighten back your bleed bolt, if the bleed bolt is leaking you will likely get the same result.
Comment: How do you bleed the brake from the tires? I find it easier to use the bleed nipple on the brake caliper.
Comment: yes, it is a brake caliper.


Properties inherited by the coarse moduli space

Question: Let $\mathcal{X}$ be a regular, seperated Deligne-Mumford stack and $X$ be the coarse moduli scheme associated with $\mathcal{X}$. Then, is $X$ regular? I guess this is a basic fact but am not able to find any reference.
Answer: Not at all. Take for instance the quotient stack of $\mathbb{A}^2$ by $\pm 1$. The coarse moduli space is the quadratic cone.
Comment: If it is OK for you to think of the stack as of a global quotient stack by a finite group action, the condition is that the group is generated by complex reflections.
Comment: If $\mathcal{X}$ is one-dimensional, then $X$ is regular. If the coarse space map $\mathcal{X}\to X$ is etale, then $X$ is regular (and $\mathcal{X}\to X$ is a gerbe). If the stacky locus of $\mathcal{X}$ is pure of codimension one, then $X$ might be regular (I don't remember the precise statement).
Comment: @user43198: https://en.wikipedia.org/wiki/Chevalley%E2%80%93Shephard%E2%80%93Todd_theorem
Comment: Is there any known additional condition that we can impose on the stack to ensure that $X$ is regular?
Comment: @AriyanJavanpeykar I am new to the language of stacks. Could you suggest some reference where I can find your answer or Sasha's?
Comment: @Sasha Could you please suggest some reference for your comment.


How does a margin account work?

Question: If you open a margin account, does this mean that you are putting your OWN money in the margin account which is supervised by a broker and to whom you pay interest to?
Answer: A margin account is one where you can borrow money from your broker to buy securities.  The loan is collateralized by your cash and/or marginable securities.  You pay interest to the broker on cash borrowed.  However, you do not have to borrow cash from your broker.
Some strategies cannot be done in a cash account and require a margin account: shorting securities, selling uncovered options...
A managed account is one that is supervised by a broker, to whom you a fee.  The fee tends to be an annual percentage of the value of your account.

How does a margin account work?