How do I restore my mouse sensitivity/acceleration settings to their defaults

Question: I changed the mouse sensitivity/acceleration settings in System Settings\Mouse and Touch Pad. How do I restore these settings back to their default values?
Answer: In Ubuntu 12.10 per-user mouse settings (and others too) are managed by settings daemon, and their configuration is stored in dconf database. To restore the default settings you want to set the values new users have on those fields = -1 (or resetting them).
Steps to set default per-user settings, using dconf-editor (low-level graphical tool):

Launch dconf-editor. If not installed, install using sudo apt-get install dconf-editor.
Browse/choose directory (on the left side) to /org/gnome/settings-daemon/peripherals/mouse.
Change values of motion-acceleration and motion-trheshold to -1.

Steps to set default per-user settings, using dconf (low-level terminal/console tool):

Check if it's there (run dconf help). If not, install using sudo apt-get install dconf.
Run in terminal dconf reset /org/gnome/settings-daemon/peripherals/mouse/motion-acceleration
Run in terminal dconf reset /org/gnome/settings-daemon/peripherals/mouse/motion-threshold

Steps to set default per-user settings, using gsettings (high-level terminal/console tool):

Check if it's there (run gsettings help). If not, install using sudo apt-get install libglib2.0-bin.
Run in terminal gsettings reset org.gnome.settings-daemon.peripherals.mouse motion-acceleration
Run in terminal gsettings reset org.gnome.settings-daemon.peripherals.mouse motion-threshold
Comment: Ubuntu 16.04 has changed it to "/org/gnome/desktop/peripherals/mouse/speed". (I was able to identify this by using the "dconf watch /" command, and then changing the setting in the settings page to see where it was stored.)
Comment: Was able to find the values, but changing them didn't make a difference for my mouse.
Comment: Did you change them only in System Settings?
Comment: No, these settings didn't appear in my system settings for some reason. Hence trying this method...
Comment: This worked for me. Sadly whenever I enter the mouse settings applet again, they move back to the minimum values.
Answer: While this doesn't directly answer your question.  I found that the sliders to the left most position did not feel like the defaults at all after messing with them.  After some research I found out the following information to fine tune how the mouse works which may be helpful to some other visiting this page.

It looks like there is a rather complex set of tuning functions available for setting the mouse behavior.  You can see all the settings here.  The most important ones are the Acceleration Profile and Constant Deceleration. Here's what I found works for me, and how I set the values.
First we want to see what the properties are:
xinput list             # Displays connected devices (Find ID of your mouse)
xinput list-props <ID>  # Displays properties of device

Next, I put my desired settings inside a script called fixmouse.sh.  I had to tinker a bit before I found these preferred values.
xinput set-prop 'Logitech USB-PS/2 Optical Mouse' 'Device Accel Profile' 2
xinput set-prop 'Logitech USB-PS/2 Optical Mouse' 'Device Accel Constant Deceleration' 2

Run the script and your mouse settings will take affect immediately. Your mileage may vary. Play with the different profiles and values for deceleration. The higher the Deceleration, the slower the mouse moves.  It might also be a good idea to drop the initial values from xinput list-props to another script called unfixmouse.sh while you are tinkering.
Comment: Thanks, PKKid. I'd upvote for this if I had enough rep, it's nice to have a bit more detail and control than the GUI provides.
Answer: What I've found is that deleting the gconf mouse folder resets everything to defaults.  The slider bars don't change, must be cached somewhere in gnome.

Using the terminal:
Open a terminal (Ctrl+Alt+T), perform the following command:
rm -fr ~/.gconf/desktop/gnome/peripherals/mouse
From Nautilus:
Press Ctrl+L
Paste or type ~/.gconf/desktop/gnome/peripherals
Open context menu (right click of mouse)
Select the option Move to Trash
Comment: Does this work with 12.10?
Answer: Ubuntu 18.04 and above

Install the dconf Editor application

To install from the Ubuntu Store, search for dconf Editor
To install from the command line, run sudo apt install dconf-editor

Open dconf Editor
Navigate to /org/gnome/desktop/peripherals/mouse
Right-click on speed
Click Set to default
Answer: The default value for both is leftmost - Acceleration is slowest and the Sensitivity is lowest.
Comment: I don't think this is quite true.  I believe that the sliders were by default to the left most position when I first opened the app.  However, I have also messed with these bars, and now putting them back to the left most position makes my mouse feel god awful slow (which wan't the case after I first installed; 12.04).  I can't even get my mouse across the screen anymore without lifting my mouse.
Comment: I have the same experience @PKKid. I've tried the accepted solution to no avail. I don't mind the speed/acceleration I've set the mouse too, but for some reason whenever moving from my right monitor to my left if I'm not going painfully slow my pointer ends up completely to the left side of my left monitor.
Answer: [Note: I have Ubuntu 14.04 and this technique worked for me]
I used tpconfig (no GUI) to reset my touchpad which got screwed up because I tried to tweak settings in "gpointing-device-settings" which is a GUI btw.
you can do a
sudo apt-get gpointing-device-settings

and play with mouse/touchpad settings but mind you there is no option to reset to factory.
Or, please google for "tpconfig" to get more info on it. to install it, you can do a:
sudo apt-get tpconfig

there is an option:
sudo tpconfig --device=DEVICE

you can set a different device here, so please do some research on that.
Comment: You should try to provide a complete answer without "do some research" or "use google".
Comment: roger that guntbert. this is my first ever post.
Answer: Ubuntu 18.04 and above
From terminal:
gsettings reset org.gnome.desktop.peripherals.mouse speed

Pointer speed for mice. Accepted values are in the [-1..1] range (from unaccelerated to fast). A value of 0 is the system default.

Here how to backup/restore the custom setup.


How can a high schooler get more involved in mathematics?

Question: For a high school student interested in majoring in math and learning more about math, what kinds of mathematical research can a student in high school get involved in? How can a high school student get involved? If a high school student does conduct research, what mathematical journals would be willing to publish their work? Also, what other ways are there for a high schooler to get involved in more complex mathematics?
Comment: This appears to be a question about educating students in high school about research and thus I have added the education tag
Comment: @Don: This appears to be a question that is of great significance. Therefore, I request you to add an answer as well.
Comment: Has OP considered some summer programs designed for high school students, such as http://math.mit.edu/research/highschool/?
Comment: Well, the hard part is knowing if you're work has been published before. Consider the case of the great mathematician Ramanujan. From a very young age he showed extraordinary mathematical ability but as he wasn't formally educated he did not realize that much of what he had discovered was already out there. So, as general advice, be well aware of your research topic. As for a topic, choose one that interests you the most.
Comment: @DonLarynx I have looked at the PROMYS and Ross programs. While they look interesting, they seem to have a heavy focus on number theory, and I am not certain that I want to necessarily focus on number theory.
Comment: @okarin: Search (for what you're interested in)
 and you will (certainly) find.
Comment: I second what Don Larynx says. I also recommend trying out undergrad summer classes. Some schools offer calculus, linear algebra, physical mathematics, real analysis, and abstract algebra. Try to get ahead, so that you can take grad classes by your third or fourth year of college.
Comment: @user97554: This may be common in the US but this sure ain't a universal thing.
Comment: I have removed ([tag:high-school]) tag; see [this discussion](http://meta.math.stackexchange.com/questions/2570/can-we-please-delete-the-high-school-tag) on meta.
Comment: I have a research project you could do on finite subdivision rules (https://en.wikipedia.org/wiki/Finite_subdivision_rule).
Comment: @BrianRushton What would such a project entail?
Comment: @okarin Seeing what finite graphs can be the history graph of a subdivision rule.
Answer: Not to be a downer, but I've found that it's hard for even an undergraduate majoring in math to get involved in original mathematics research (from personal experience). The issue is that there's not a lot of low hanging fruit in mathematics that would lend itself to be a good project for a high schooler or undergrad mathematician. However, I don't mean to suggest you shouldn't try. Ask professors at local universities if they have any projects that might be accessible to a high school student or undergrad (perhaps provided you do a little background reading on your own to familiarize yourself with the concepts necessary). As an undergrad, I've been extremely lucky with "research type experiences": my freshman year, I approached my honors calculus professor about doing research. He let me down saying essentially what I told you, that it takes a lot of advanced background knowledge in mathematics to be able to do original research (simply because so much has already been done), but he also gave me the opportunity to try to solve an already solved problem that I didn't know the solution to (the problem was "how many ways can a positive integer $n$ be written as the sum of four squares?"). This project led me to study elliptic curves, modular forms, and other sorts of awesome advanced maths I never though I'd be doing as a freshman in college. So, even if you don't get involved in original research, you might still find an awesome experience.
On the other hand, I'm an undergraduate junior now and actually working on original research. You might get lucky and find someone who has a problem that's accessible with minimal background information, although you might have to work extremely hard (read: you'll most definitely need to work extremely hard) to catch up on that "minimal background information" (in my case, I needed to familiarize myself with a lot of category theoretic jargon and concepts before I could approach the problem at all). However, I am currently involved in actual research, and it's awesome. Don't give up! Even if you don't find anyone with an accessible project, you might still find people who have suggestions about what you can look at on your own. In high school, I didn't have access to anyone who was able to tell me about modern mathematics and modern research, so I found a subject that I was interested in (topology) and tried to learn it for myself. It's certainly not the same as actually doing research, but self study often presents many of the same problems to students as research: you don't know what to do, you might not know anyone who has experience working with the concepts you're struggling with, and you need to be very clever to overcome the obstacles you find in the problems (of course, the difference is that if you really want to, you can probably find the solutions online for something you're self learning, whereas the solutions most likely won't be easily available online when you face a problem in your research).
As for publishers, I'm not really sure what options there would be if you find research to get involved in. But that shouldn't be your goal anyway. You've got a lot of time; focus on finding something interesting and trying to understand it (even if it's been understood by others before) - that's a lot of what research is about anyway!
Edit: I see that the Ross and PROMYS programs are being mentioned in the comments. I am a little biased, but I believe that these programs are fantastic ways to be introduced to research style mathematics in an accessible manner as a high school student/undergraduate. Even if you aren't interested in number theory, you'll still encounter the same issues when facing research in any area - so struggling through number theory may provide valuable intuition/experience for struggling in the future in other areas of mathematics (it also helps that many deep ideas from number theory can be hinted at/worked on without introducing a lot of complex jargon). And while these programs are based on number theory, other aspects of mathematics become involved as well - so you wouldn't only be finding out about number theory, but you'd be learning about all sorts of awesome stuff (from analysis to category theory)! You should definitely look for things that interest you, but when it comes to a "research experience," these types of programs might be some of your best bets as a high school student. Don't dismiss them because you think you're not interested in number theory - there's a lot of valuable knowledge to be gained from struggling with any subject, and who knows? you might find you actually are interested in number theory after all!
In the end, one of the most valuable research experiences you can get is that of struggling with a challenging problem: there are different ways to get that experience, and not all of them involve actually doing research. Look around, keep your mind open, and ask questions - even if you don't wind up doing original research, you'll be well ahead of the game.
Answer: From personal experience (either as a student or a teacher), here are my recommendations:

If you are near a university and can afford it, see if you can take math classes at the university in place of your high school math classes. Talk to the professors and see if they would be willing to have you in the class (they probably will, since they were probably in a similar situation at your age). This is how I got really into math, and it was probably the best decision I've ever made. If you can't afford it, you may still be able to audit classes, although I don't know if you could get out of high school classes for this.
I would recommend against trying to do original research in high school. I certainly tried and failed; it is only recently that I've gotten to the point where I can do original research on any mathematical problem, and even now I'm only really at that point for one specific problem. However, I would recommend reading the cutting edge research on some problem you find interesting. The first time you try to read a cutting-edge paper, you'll probably run into fifty terms you do not recognize. Looking up half of them will give you more terms you've never seen. It's a deep rabbit hole, but after a while you can probably develop the background necessary to understand some of the work on a current problem. I found that having a particular problem to focus on really motivated me to learn, and it eventually developed into original research!
Many universities have weekend and summer programs in mathematics. You can learn a lot at these, particularly if you are enthusiastic and make a point to interact with the staff, who are usually college math students. My personal experience is as a counselor for the YSP and VIGRE programs at the University of Chicago, which I would recommend if you are near Chicago, but I'm uncertain whether they will continue since the professor who directed them passed away a few days ago.
Pick one or two accessible textbooks, and try to read and understand them. Do all the exercises, or at least all the hard ones. My first textbook was Modern Algebra: an Introduction by John Durbin, which I think is quite good if a little on the easy side. Spivak and Baby Rudin are standard recommendations; by most accounts they are quite good but I can't speak on them personally since I've never read them. As more advanced books go, I rather like the Dover and Springer Undergraduate Texts in Mathematics series.
I would recommend visiting math.stackexchange.com, but that feels a tad redundant :)
Answer: The best way for any talented high schooler to get involved in mathematics is just to learn as much of it as he or she possibly can. Doing research in it isn't realistic for high schoolers except for the occasional prodigy who's doing calculus by 12 years old. What you should do is see if an intensive program for high schoolers is available that allows a student to do a thesis before entering university-something like the VIGRE program at the University of Chicago.
As for any subjects you could attempt to produce original results in that don't require an extensive background, you could certainly try combinatorics. There's a reason why that's the traditional proving ground for students trying to begin research at a young age.
The standard book acting as a gateway for talented high schoolers into advanced mathematics has been Micheal Spivak's Calculus and it's hard to imagine better preparation then that.
Good luck!
Comment: You don't have to be a prodigy to do calculus while you're twelve. Any twelve year old can mug up those formulas within a week or two and integrate and differentiate with ease. It's all about having the right people to guide you (or give you resources such as the formula sheets). This is something I learnt very late in my life and it's something that most people go without realizing.
Also, Thank you for suggesting that excellent book, I know a kid in the mirror who'd be much pleased to read it.
Comment: @Nick I did that when I was 8 , today I am 14 and I do research in analytic number theory , and complex analysis .Its generally fun in research especially when you are under age.
Comment: @Shivam If you're not BSing us, then you're a rare talent and probably was given all kinds of direction and encouragement. I'm not sure if doing that so young is really healthy for your overall development as a human being, but every case is different. My point is you're a rarity. I think most students that young who try it will fall flat on thier butts and the discouragement will be damaging.
Comment: @Mathemagician1234 thankyou for your kind words .Actually I wasn't given any encouragement till 26 Jan last year . I developed this thing myself , by reading books online , visiting library and doing research work when my parents didn't know - in the night or hiding in my school books ...Then finally when my parents came to know about my talent through local math Professors ,then encouragement and support was provided. And for mathematics passion is enough .
Answer: First off, I am not a professional mathematician but I can share what got me interested in math and a life-long love of math (I am 60+). Mathematical puzzles, recreational math and elementary number theory. In my view, elementary number theory is the most fascinating field of mathematics because problems are easily stated and understood but are frustratingly difficult and challenging.
Good luck and wish you the very best.
Comment: Recreational Math! That's what gets most people interested. I know a girl named Vi Hart can give anyone a fair dose of fascinating ponderings on several topics of mathematics. Usually, her topics are interesting to individually research on.
Comment: I will check it out. For pure pleasure, read Dodgson, in my view one of the most talented *non-professional* mathematician. He was *just* a highschool math teacher but came up with some wicked problem. The world knows him as Lewis Carrol, the author of Alice in Wonderland but his mathematical books are all gems.
Comment: @44197: Mind - Blown! Thank you for that information.
Answer: I agree with the responses above that one way to be more involved is to learn more through reading to get an idea of what are some cutting edge problems and math today. Math Stackexchange is a good site, but it can be quite tough for a high school student.
Is Research Possible for a High School Student?
However, I would think otherwise to the point that there isn't much opportunities for original Math research for high school students. Even though it is true that with less prior knowledge equipped, there is much less scope for research. However, fields such as combinatorics are usually more of understanding and reasoning and can be done even by a high-schooler! But of course you need to be ready to put in much hard work and time commitment to read through tons of papers across topics and fields sometimes because Math is simply so interconnected!
The Research Process:
To conduct a research, the most important phase is the inspiration. You do so by looking up some not so "hot" topics or math topics/problems that are not so much worked on. If you are lucky, you can find a problem to work on! :) This is always the hardest but most essential step of research. Then think through the ideas or approaches you can make to solve the problem. If you have any teachers or mentors to consult, you can do so by sharing your problems, initial researches and original ideas to the problem, and get their feedback. Here your research journey begins! :) If you still cannot managed to solve the problem in the end, at least you get this idea already at the back of your brain and perhaps one day with more knowledge and techniques at hand, you can return to the problem and solve it.
Answer: Just to briefly answer your question regarding publication; the Society for Industrial and Applied Mathematics (SIAM) maintains an "Undergraduate Research Online" Journal (SIURO), which is available at http://www.siam.org/students/siuro/.
If you are able to obtain even a small result, this might be a good venue to attempt publication. However first, put a manuscript of the paper up on arXiv and send it to a couple people who work in the field other than your advisor/supervisor/mentor. This allows you to increase your exposure and get a new set of eyes on the paper.


Macbook Notes app can't access data

Question: I was using the notes app just fine when I closed and reopened it to a pop-up message saying that it couldn't access my data. I tried reopening the app several times and restarting my computer. The message no longer shows up and just shows a blank version of the app. I can't make new notes or view my old ones. Is there a way to get my old notes back?
Answer: I give this as answer, because the command can't be given in comment mode :
You can begin by repair your user autorisations with terminal command  :
<code>diskutil resetUserPermissions / `id -u`
</code>
Comment: RE: "I give this as answer, because the command can't be given in comment mode :" --  You can give this _shell commands_ in a comment, just like this: `diskutil resetUserPermissions /  $(id -u)`

Macbook Notes app can't access data


retrieve Mysql server time using ADO.net

Question: I am using ADO.net and LINQ-to-Entities in VS2010 to connect to Mysql server, and I would like to know what is the current date and time on the server side.
Is there any method to do this using a LINQ query?
I don't want to use any SQL statements in my program.
Answer: Have you tried creating a stored procedure in MySql (assuming  you have v5 or greater) and creating a function in your EF class that calls it?


Can a theory that is now wrong be right in the future?

Question: For example, we take as granted that energy is conserved (energy conservation principle). Imagine that someone "builds" a theory where the energy conservation doesn't apply. The scientific community should reject this theory.
But what if in the future conservation of energy doesn't apply? Then the theory would be correct (assuming it predicts phenomena, is mathematically formulated etc.)? I mean we reject or accept theories based on "axioms". (It seems impossible to violate the energy conservation but we just have accepted). Does this mean that we are even in doubt if a theory is right or wrong?
Comment: I don't think so, what is demonstrated to be wrong will probably remain so. New theories can only extend other theories, it is not like general relativity or quantum mechanics will suddenly be wrong, and then the mechanistic, absolute and deterministic universe be right. It is already demonstrated that our universe is not deterministic, not absolute and not mechanistic, so : only theories that expand our body of knowledge will survive in the future.
Comment: Scientific "right/wrong" does not apply to every grand generalization. The theory one builds would have to account for the energy being conserved in the classical range, where it is observed. If it does that, while physicists may not adopt such a theory on balance, they will not reject it out of hand either. In fact, minor energy non-conservation was envisioned by some seriously considered past theories, like [BKS](https://en.wikipedia.org/wiki/BKS_theory). And we do not reject or accept theories based on "axioms" only, observations and experiments have something to do with it too.
Comment: If some of the answers below satisfies you, please accept it.
Comment: Based on some criteria about what energy conservation should mean, some physicists say that energy is [not globally conserved in general relativity](https://www.discovermagazine.com/the-sciences/energy-is-not-conserved), although there are [definitions](https://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html) involving coordinate-dependent "pseudo-tensors" where it is conserved.
Comment: Energy is not conserved, across accelerating expansion of the universe, and over short time periods & length scales. Einstein called introducing the cosmological contant his greatest blunder, because it obscured the necessity of the universe expanding. It is now considered an essential piece of physics https://en.m.wikipedia.org/wiki/Cosmological_constant#History
Answer: Question:
For example we take as granted that energy is conserved (Energy conservation Principle). Imagine someone "build" a theory where the energy conservation doesnt apply. Scientific community should reject this theory. But what if in the future conservation of energy doesnt apply ? Then the theory would be correct (assuming it predicts phenomena , is mathematic formulated etc.) ? I mean we reject or accept theories based on "axioms". (It seems impossible to violate the energy conservation but we just have accepted).Does this mean that we are even doubt if a theory is right or wrong ?
Answer:
We (I mean, contemporary scientists) do not take for granted that energy is conserved. The energy conservation law came from observations and experiments. And we do not reject or accept theories based on "axioms"; we do/don't do so based on the existing evidence. What's more, we always doubt that any currently accepted theory may be wrong. That's why we always do a lot of various experiments to verify it (i.e., to see if it's right or wrong).
Scientists nowadays use the method called "Scientific Method" (e.g., see ref 1 and ref 2) to find a theory that can account for the phenomenon in questions (see step 1 to 5 in the figure below).

Even if, such a theory (6)  is found, continuing experiments and new evidence (7) can disprove it, and a new theory has to be found by beginning the process (2 to 5) again. So, any theory can never be guaranteed to stand forever un-disproved, not even the current thermodynamic theory, Einstein's Relativity theory, or the current quantum theory.
Question: Can a theory that is now wrong be right in the future?
Answer: Yes, it can. This is because the evidence that supports the theory may not exist or because poorly-collected/misinterpreted counter-evidence is found/presents at the time when the theory is proposed. The former case can happen because the evidence exists but has not been found yet or because the technology at the time is not advanced enough to find it. The latter case can happen because the method/technology to collect the evidence may not be correct or the required knowledge to interpret the result correctly does not exist yet. For example, in the 16th and 17th century the hypothesis that the earth revolved around the sun was proposed, but it was proved to be wrong at that time because

"… if the earth revolved around the sun then there should be changes in the relative positions of the stars over the year (see Stellar Parallax       ). This stellar parallax could not be observed. Based on this and other 'facts', the scientists of the time were correct to reject the proposed hypothesis. What they did not know was that the stars were far more distant than they thought, billions of kilometres away instead of millions. Given the power of the telescopes of the time, they would not have been able to detect this parallax. ..."

The theory that the earth revolved around the sun was not proved to be correct until the eighteenth and nineteenth century when stellar parallax was finally observed. (from The Scientific Methods)
And, of course, a theory that is now right can prove to be wrong in the future. This is obvious from the figure above (i.e. when conflicting evidence to the theory is found  - step 7). Real-life examples are several past theories that are now proved to be wrong, such as the theory that the earth is flat, the Aristotle's theory of gravity (which states that objects fall at speed proportional to their mass), the theory of light that is exclusively corpuscular (such as Newton's) or exclusively wave (such as Huygens'), a classical physical theory that holds that measurements of time and distance are absolute and not dependent on observers, and a classical physical theory that concludes that physical events can be definitely predicted.
Comment: But we should also take into account Duhem-Quine thesis right? I mean even if we reformulate the hypothesis we can't test it per se.
Answer: Wait a minute -- your question states "a theory that is now wrong be right", whereas your conservation example describes "a theory that is now right be wrong".
Re your explicit question, a now-wrong theory is presumably wrong because there exists ubiquitous experimental refutation of its predictions. And that's very unlikely to change (although, very occasionally, the outcomes observed from particular experimental designs have later been found to have originally been misinterpreted). So, basically, "No", a now-wrong theory won't be right.
But, re your example, and as already pointed out, once-right theories have frequently been later found wrong. They originally agreed with the then-available observational evidence, but ultimately disagreed with subsequent observations. In many cases, the original theory turned out to be a sensible approximation to the later-and-better theory. An example where that's not the case is the ancient Greek epicycle theory of planetary motion. Epicycles preserved the idea that the planets revolve around the Earth, but that entire conceptual basis was eventually found completely wrong.
Answer: There was that period of time between 1690 and 1801 where Huygens's Treatise on Light (wave theory of light) was considered bonk while Newton's Opticks (corpuscular theory of light) reigned supreme.
Answer: Absolutely. I'm not aware of any examples, but we have no proof that the laws of physics are fixed. Every day, we wake up and see the laws of physics are the same. We wake up in our beds and gravity still works. Most people [citation needed] would go as far as to bet that they won't change tomorrow either. However, we have no proof of that.
Answer: I think it is a matter of consensus among the scientific community. Nothing is written in stone and theories are accepted as long they can pass the checkup against the current framework of facts taken as true by the community shaping our conception and knowledge of reality.
Just proving wrong a single fact doesn't automatically make valid a discarded theory that was based upon the opposite of the fact, it needs to be again compared against the framework to ensure that all conditions are satisfied. In other words, the theory makes sense within the new knowledge about reality.
Answer: The more relevant question is whether a theory can be right, or just good enough to explain what we observe.
A theory that is wrong is wrong and one that is right is right, and clearly one that is good enough now may not be good enough in the future. But one that is not good enough now involves an observed contradiction or leaves a gap.
But what we have observed, changes.  If there is an explanation that proves the observed contradiction was only apparent, then our currently inadequate theory might then suddenly be adequate. And if another theory fills the gap, or proves it cannot be filled then this one may suddenly become adequate, too.
An example might be Einstein's cosmological constant. It was inadequate at the time because there was no reason for it, it left an explanatory gap, and it seemed too ad-hoc to be realistic. But now we find there is another force at play, 'dark energy', and it would give a reason for this constant and make the theory less ad-hoc and therefore appropriate.
Answer: I suppose that it can be.
If a hypothesis is unable to be proven today, or if it goes against established theories without sufficient evidence to overthrow said theories, it will be considered "wrong".
Should the relevant theory be proven wrong by a 3rd party in the future, it is possible that the original hypothesis can now be shown tl be correct, using the new knowledge.
In practice, i don't see this happening, but i suppose that it is a hypothetical possibility


Chainload syslinux from GRUB2 - show syslinux.cfg menu

Question: I am using a Clonezilla live USB disk to reimage systems.
In accordance to what is explained in http://clonezilla.org/fine-print-live-doc.php?path=clonezilla-live/doc/99_Misc/00_live-boot-parameters.doc my disks prompts me with the menu contained in syslinux.cfg for all systems except the very latest ones that are UEFI machines (and have the BIOS configured to boot from UEFI devices first) where I am prompted with the grub.cfg menu.
Given that I heavily customized my syslinux.cfg menu I would like to modify the grub.cfg file to only automatically chainload to syslinux so to show the syslinux.cfg menu in all cases.
Is this possible at all?
How?
On the disk there is GRUB2 and my understanding (from looking around on the Internet) is that is shall be possible, but I did not understand yet how. Any help is appreciated.Edit:I would like to clarify that the system boots using grub without issues selecting any of the options that are in the grub.cfg menu by default as provided by Conezilla download, but what I would like to do is to show the menu of syslinux (in syslinux.cfg) instead of the default menu in grub.cfg
Second edit, how I did it:In the end the proposed solutions did not work for me, so I simply made the 'EFI\boot' folder "unavailable" (renamed it); this way the UEFI boot fails and the system boots from syslinux as on the older system: no modification to the BIOS, no new menu, no chainload...
Comment: I guess, you can use `configfile` parameter inside grub.conf to chainload the syslinux.cfg
Answer: After 4 years... :)
Try this:
menuentry 'menuentry' {
    set root=(hd0,1)
    syslinux_source /path/isolinux/isolinux.bin
    syslinux_configfile /path/isolinux/isolinux.cfg
}

Comment: Please elaborate a bit and explain why this solves the problem.
Answer: This suggest that it was some bugs related to that and was some patches, so it is hard to know for sure: https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/469568
First, if your OS updates grub it will regenerate grub.cfg and wipe out your configuration, so do not modify /boot/grub.cfg manually instead modify files in
/etc/grub.d ( file named like 40_custom or something like that ) and call grub-mkconfig -o /boot/grub/grub.cfg.
You could try something simple like this:

menuentry "Syslinux root drive" {
set root=(hd1,3)
chainloader +1
}

(hd1,3) is sdb3 disk partition, grub supports identification by uuid, so it possible to create setup in which your partition would be detected by all PC's. However in my experience sometimes this is not enough.
You could also try something like chainloader (hd1,3)/path/to/syslinux/isofile.bin
If everything fails, it is possible to boot from iso with syslinux in it, but it seems that in your case this is not an option.
Comment: I first tried this from the grub command line (press c once in grub), I identified my syslinux.cfg partition and tried 'chainloader (hd0,msdos2)+1' directly but I get the error 'invalid EFI file path'. Please note that the content of the partition above dos not contain any .bin file. (I also edited the question for additional clarity)
Comment: It probably doesn't, its name and binary format extension (.bin) depends on distro (live cd's usually have bin to be able to boot with syslinux and isolinux, but in your case it is probably .bs file, watch here for commands http://www.syslinux.org/wiki/index.php/SYSLINUX#LABEL_command). However I am now researching one thing: doesn't booting kernel directly with casper module (aka live cd/ live usb mode) doesn't run it's bootloader menu. After few minutes I'll write results.
Comment: OK, I see that candidates are the .c32 files that I have in that folder. More precicely this is the content of the folder:'chain.c32', 'menu.c32', 'reboot.c32', 'vesamenu.c32', 'memdisk', 'syslinux.cfg'excluding the cfg file, shall I try the other one by one? Looking around I understood that the chain32 is supposed to be used for chailoiding in the other direction (so not what I need), am I wrong?
Comment: Well calling casper doesn't invoke bootloader menu. I have no idea how to archieve this. If that would help I have my own grub chainloading example to grub, but I doubt that it have any use with syslinux: `menuentry 'Archlinux The Latest' {
insmod ext2
set root=(hd0,6)
multiboot /boot/grub/i386-pc/core.img
}
`
Answer: you have to do a directory install instead of a boot sector install. if you do a boot sector install then dd the first 512 bytes of the partition to a file and chainload to that file. worked for me.
Comment: This may be correct, but it could benefit from a bit of explanation about _how_ to take the steps described (and from proper capitalization).


Positivity, Causal Inference and Machine Learning methods

Question: I ran into a problem where the predicted probabilities of being treatment/control from a machine learning model (the XGB model) matches the actual outcome almost exactly and have area under the curve (AUC) of 0.9999. On the other hand, the logistic regression achieved an AUC of 0.5. However, I cannot use the greedy matching algorithm to find any matches for the treatment if I use the XGB propensity scores. One of the earlier posts here mentioned this problem: How to use propensity scores that exhibit separation. So my question is: in order for the matching algorithm to work, do we have to give up the better machine learning prediction model for an inferior logistic regression? This seems a little counterintuitive.
Answer: You are judging your propensity score models on the wrong criteria. The only criteria you should use to assess how good your propensity scores are are how well they achieve balance and the remaining effective sample size when conditioned on (i.e., using matching or weighting). I explain this in my answer here. You should not use AUC to assess propensity score models; the fact that XGB has a higher AUC than LR doesn't mean anything. It's simple to overfit a propensity score model so that you get perfect prediction of the treatment; this doesn't actually mean anything about positivity and doesn't mean the overfit model is preferable.
Comment: Thanks for the very helpful answer. But aren't they related at all? I mean a good model that can achieve balance should at least yield an AUC better than 0.5 right? If a model is completely unable to distinguish between treatment and control, let's say everyone gets a predicted probability of 0.5, then I would think the resulting match will be poor right?
Comment: They might be related but there's no point even computing accuracy if your goal is balance. Such a low AUC suggests there is already good balance in the dataset.
Comment: Actually they are not balanced at all in the dataset...that's why I am so puzzled.


Short story about intelligence being only an evolutionary stage to ensure interstellar propagation

Question: Main character is a schoolteacher on one of the first human colonies in space. He is puzzled over and concerned with the uniform lack of intellect he is observing in his students, especially since they are the progeny of accomplished parents who were hand-picked to found this colony. None of his students are mastering any of the material, and he is becoming concerned that their generation will be unable to maintain the colony. Teenage pregnancies become the norm, and one of the students proudly shows the teacher her baby, which has distinctly simian characteristics. The teacher comes to the realization that humans aren't intrinsically intelligent -- intelligence is just one step in the species' propagation cycle (like a pretty flower) that lasts only as long as necessary for it to build up the technology required to reseed on another planet, then is discarded until the next cycle.
Answer: The Locusts by Larry Niven and Steven Barnes
A colony expedition to Tau Ceti ends up de-volving into apelike creatures.

There are no men on Tau Ceti IV
...
There are things in the forest. They prefer it there, but will occasionally shamble out into the grasslands and sometimes even into the town. They themselves do not understand why they go: there is no food, and they do not need building materials or other things which may be there for the scavenging. They always leave the town before nightfall arrives.
Comment: I appreciate the prompt recognition and response! It's exactly the story I was remembering, though my memory of it was obviously inaccurate in some details.
Comment: @LarrySpencer You're most welcome, thanks for the prompt acceptance. This question will get closed as a duplicate under the house rules since there is another question on the site with an accepted answer about the same story. But there's nothing wrong with that, your question will remain on the site and can help future readers locate the story.


How many cases can draw diagonals?

Question: Imagine a n_regular polygon that vertex is named by 1 to n.
We know can draw (n)(n+3)/2 diagonals in n_regular polygon,Also know if we want to draw Maximum diagonals that not intersecting each other inside the n_regular polygon is n−3 diagonals.
For example for Flat hexagon we can draw Maximum 3 diagonals that we can do it with 14 cases.(you can find it easy)
Now imagine we want to draw diagonals that have 2 condition like this:
1- any vertex is not connected to 2 before and 2 after vertex.
2- any 3 vertex is not exist that intersecting two by two inside the n_regular polygon.
It's easy to understand that the Maximum of diagonals can draw is 2(n−5).
But the question is how many cases can draw diagonals that Applicable 2 above condition?
For n=6 we can draw 3 cases that necessitate this 2 condition . If we labeled regular when n=7 we have 2(7−5)=4 diagonals and we can not use this vertexes {1,4},{2,5},{4,7},{3,6} because we ignore the second condition.
Answer: I don't understand what you mean by your 2 conditions (the english). Let me translate up until that point.
Suppose we have a regular $n$-gon with vertices labeled 1 to $n$. There are $n(n-1)/2$ possible diagonals. The maximum number of non-intersecting diagonals is $n-3$, and if we draw them we get a triangulation. The number of ways to triangulate an $n$-gon is the Catalan number $C_{n-2}$. For example, the number of ways to triangulate a hexagon is $C_4 = \tfrac{1}{5} {8 \choose 4} = 14$.
Now instead of non-intersecting, suppose we impose the following two conditions:
1? 2?

How many cases can draw diagonals?


Acoustic problem of intonation low on neck

Question: I am a bass player for over 35 years. Also play guitar. I have worked on my own electrics, setting intonation, etc. I have an acoustic. When I tune it, the low E, fretted at the 2nd 3rd frets are sharp. I checked on a tuner. Do I need to lower the nut where the E passes. Thanks in advance.
Comment: I always have to make compromises when tuning the E string, if the open E is well tuned , the F# and G are sharp. It  is like Tim says. But as an experienced Bass player you will know if the neck is bent or you are pressing not quite straight the strings.
Answer: Depends on several factors. If the action is high, pressing a string anywhere will sharpen its pitch due to it being stretched. It will show up more at the lower notes. That high action could be due to the nut being too high, or the neck relief being too great, or the bridge being too tall. Or all of these.
Old strings sometimes do strange things, so a change may be all it needs. Tuners sometimes need a second to settle, and often show sharp initially.
The intonation could be way out on only that low E string. Check it's good using 12th and 19th fret harmonics. Last ditch effort - it may be a duff guitar, so take it to a luthier for checking.
Comment: Ok.  I know the intonation is sharp for the most part. It's not an expensive guitar. That E just sticks out to me when I play a G chord. Thanks for all your input.
Comment: In that case I'd try to move the saddle for bottom E string away, making it longer. A 12th fret harmonic/fretted note check will help determine.


How do I propose a tag on a beta site?

Question: I would like to add a new tag to Board & Card Games Stack Exchange, but of course it requires 1500 reputation. This will be pretty hard to get on this site since it is in beta. Is there an acceptable way for me to request a tag be added by someone with 1500 reputation?
Answer: On beta sites like Boardgames, you can already create tags when you have 150 reputation. If you don't have the necessary reputation, you can ask on the site's own Meta to have the tag created, but you need to provide good arguments to do so. Other alternatives are the site's chat, or ping another high-rep user who was involved in the question.
Comment: Thank you, I didn't know about any of these options!
Comment: @Max Better make a research before asking, finding this is trivial.
Answer: Tags cannot be created unless there are questions existing that fit the tag.  For Boardgames.SE, if there is a particular game that you are interested in, but there aren't any questions about that game, you won't find a tag for it yet.
If there are already questions about that game, but no tag yet, you can ask about creating that tag on meta.  If there aren't any questions yet, but you have a question, feel free to ask it.  Most likely, a high-rep user will come by and create the tag after you ask the question.
Comment: I was going to ask a question about warhammer 40k which they do have tag for that but I wanted to add apocalypse as well which is a format of 40k. The tag for apocalypse doesn't exist and I wanted to request it. Thanks for the response.

How do I propose a tag on a beta site?


Is it possible to express a vector using cross product with another vector?

Question: I was wondering if it was possible to find $\overrightarrow{a}$ when it is given that:
$$ \overrightarrow{a} \times \overrightarrow{b} = \overrightarrow{c}$$
Vectors $\overrightarrow{b}$ and $\overrightarrow{c}$ are known. How can I express vector $\overrightarrow{a}$ using $\overrightarrow{b}$ and $\overrightarrow{c}$??
Comment: The different possible vectors $\vec a$ (yes, there are more of them) all lie along a line that has direction parallel to $\vec b$.
Comment: Not uniquely ${}$
Answer: $\underline{a}$ would have to be a vector perpendicular to $\underline{c}$ but not parallel to $\underline{b}.$
You would therefore have to find parameters $\lambda$ and $\mu$ so that, for example $$\underline {a}=\lambda\underline{b}+\mu\underline{b}\times\underline{c}$$ where $\mu\neq0.$
We then have $$\underline{a}\times\underline{b}=(\lambda\underline{b}+\mu\underline{b}\times\underline{c})\times\underline{b}$$
$$=0+\mu(\underline{c}(b\cdot b)-\underline{b}(b\cdot c))$$
But $b\cdot c=0$ since they are perpendicular, so $\mu$ is predetermined and has value $\frac{1}{(b\cdot b)}$ and $\lambda$ is arbitrary.
So while $\underline{a}$ is not unique, it can be found for specific non parallel vectors $\underline{b}$ and $\underline{c}$
Comment: @Dr.MV..true, but how does this relate to my answer?
Comment: @Dr.MV but $(\underline{b}\times\underline{c})\times\underline{b}=\underline{c}(b\cdot b)-\underline{b}(b\cdot c)$ and $b\cdot c=0$
Comment: Yes.  I had incorrectly thought that $\mu$ was a free parameter.  After reading again, I see it is not.  So, a +1
Comment: Many thanks @Dr.MV! Your very helpful comments have prompted me to expand on and clarify my answer.
Comment: You're welcome!  My pleasure David.  -Mark
Answer: As mentioned elsewhere, only the components of $\vec{a}$ perpendicular to $\vec{b}$ can be found.
Use $$ \vec{a}_\perp = \frac{\vec{b}\times\vec{c}}{\| \vec{b} \|^2} $$
Proof
Vector $\vec{a}$ is assumed to contain both perpendicular and parallel components to $\vec{b}$ such that $\vec{a} = \vec{a}_\parallel + \vec{a}_\perp$.
Now form $\vec{c} = \vec{a} \times \vec{b}$
$$ \vec{c} = (\vec{a}_\parallel + \vec{a}_\perp) \times \vec{b} $$
and use the formula above
$$ \vec{c} = \left(\vec{a}_\parallel + \frac{\vec{b}\times\vec{c}}{\| \vec{b} \|^2}\right) \times \vec{b} $$
Since $\vec{a}_\parallel$ is parallel to $\vec{b}$, it stands that  $\vec{a}_\parallel \times \vec{b} =0 $
$$ \vec{c} = \frac{ (\vec{b}\times\vec{c})\times \vec{b} }{\vec{b} \cdot \vec{b}} = \frac{\vec{b} \times (\vec{c} \times \vec{b} )}{\vec{b} \cdot \vec{b}} = \frac{\vec{c} (\vec{b} \cdot \vec{b}) - \vec{b} (\vec{c}\cdot\vec{b}))}{\vec{b} \cdot \vec{b}} = \vec{c}$$
which is an application of the vector triple product. The above is true since $\vec{c}\cdot\vec{b}=0$ with them being perpendicular to each other.
Comment: I think you have a sign error when you use the triple product? Moving $b$ to the left gives you a minus, which should then appear in the answer too?
Comment: No because, I flipped the order of this $(\vec{b} \times \vec{c})$ also. $$ (b \times c) \times b = - b \times (b \times c) = b \times ( c \times b)$$
Comment: Ah, true, my bad. Then our answers match.
Answer: Generally this is not possible. If you have the equation
$$
\overrightarrow{a} \times \overrightarrow{b} = \overrightarrow{c} \tag{1}
$$
for arbitrary $\overrightarrow{b},\overrightarrow{c}\in \mathbb{R}^3$ it is not always possible to find a proper $\overrightarrow{a}$, simply because it might not exist.
As it was already pointed out in the answer of @DavidQuinn, the resulting vector  $\overrightarrow{c}$ is perpendicular to $\overrightarrow{a},\overrightarrow{b}$ and therefore to the $\operatorname{span}(\overrightarrow{a},\overrightarrow{b})$.
So for example if we choose $\overrightarrow{b}=\overrightarrow{c}$, then
$$
\overrightarrow{a} \times \overrightarrow{b} = \overrightarrow{c}=\overrightarrow{b}
$$
is not even well defined (and we don't need to speak of a solution for  $\overrightarrow{a} $ of any kind).
So let's now assume $(1)$ is well defined - which seems to be your intention - then if we find a solution, it is for sure not unique (as @Arthur already pointed out). This is because the following holds
$$
\overrightarrow{a} \times (\overrightarrow{b}+\overrightarrow{c}) = (\overrightarrow{a} \times \overrightarrow{b})+(\overrightarrow{a} \times \overrightarrow{c})
$$
So assume we've found $\overrightarrow{a}$ which solves $(1)$, then we can simply add any to $\overrightarrow{b}$ parallel vector $\overrightarrow{d}$   and $(1)$ would still hold, because
$$
(\overrightarrow{a}+\overrightarrow{d}) \times \overrightarrow{b} = (\overrightarrow{a} \times \overrightarrow{b})+(\overrightarrow{d} \times \overrightarrow{b})=(\overrightarrow{a} \times \overrightarrow{b})+\overrightarrow{0}=\overrightarrow{c}
$$
Unfortunately, I am not aware of an algorithm which would gives us a solution $\overrightarrow{a}$ in the first place.
Answer: Assume $b, c\not = 0$. Note first that we must have $(a, c), (b, c) = 0$. Choose some vector $b'$ orthogonal to both $b$ and $c$, and write $a = \alpha b + \alpha' b'$. Then $a\times b = \alpha' (b\times b')$; and since $b, b', c$ are pairwise orthogonal, we have $b'\times b = \beta c$ for some constant $c\not = 0$. Thus $\beta$ determines $\alpha'$, and $\alpha$ is arbitrary. Specifically, for $b' = b\times c$, we have $b'\times b = |b|^2 c$ and thus $\alpha' = |b|^{-2}$.
Answer: Why is everybody assuming 3-dimensional vectors? There is a very intersting cross product in seven dimensions as well; it is anti-commutative, therefore $\mathbf a\times \mathbf b= -\mathbf b \times \mathbf a= \mathbf c$ and can be written in a matrix form:
$$    T_{\mathbf x} = \begin{bmatrix} 0 & -x_4 & -x_7 & x_2 & -x_6 & x_5 & x_3 \\ x_4 & 0 & -x_5 & -x_1 & x_3 & -x_7 & x_6 \\ x_7 & x_5 & 0 & -x_6 & -x_2 & x_4 & -x_1 \\ -x_2 & x_1 & x_6 & 0 & -x_7 & -x_3 & x_5 \\ x_6 & -x_3 & x_2 & x_7 & 0 & -x_1 & -x_4 \\ -x_5 & x_7 & -x_4 & x_3 & x_1 & 0 & -x_2 \\ -x_3 & -x_6 & x_1 & -x_5 & x_4 & x_2 & 0 \end{bmatrix}.
$$
The cross product is then given by
$    -\mathbf{b} \times \mathbf{a} = -T_{\mathbf{b}}\cdot \mathbf{a}=\mathbf{c}$. Calculate $-T_{\mathbf{b}}^{-1}\mathbf{c}$ (if possible!) and you're done...
Comment: I think the GA calculation in my answer would extend to this case too, though dealing with the [extra trivector](https://en.wikipedia.org/wiki/Seven-dimensional_cross_product) will probably introduce some new complications.
Comment: There is also a 6 dimensional cross product used in screw theory $$[v\times] = \begin{vmatrix}
  0&0&0&0&-v_6&v_5\\
  0&0&0&v_6&0&-v_4\\
  0&0&0&-v_5&v_4&0 \\
  0&-v_6&v_5&0&-v_3&v_2\\
  v_6&0&-v_4&v_3&0&-v_1\\
  -v_5&v_4&0&-v_2&v_1&0\\
\end{vmatrix} $$ with $[v \times]u = -[u \times]v$. Also the dot product with the results are zero.
Comment: @ja72 post another answer!  Every cross product should be welcome...
Comment: You know that $T_{\rm x}$ is singular right? See http://mathworld.wolfram.com/AntisymmetricMatrix.html
Comment: @ja72 I haven't checked and tried to point that out with "(if possible!)". Thanks for checking...
Answer: The question is easy to answer using geometric algebra (GA). Let me first state the answer (which is of course the same as reached in the answer by ja72) to pique your interest:
$$
a = \frac{1}{|b|^2}(\alpha b - c \times b)
$$
where $\alpha$ is an arbitrary real number, and $b$ must be orthogonal to $c$ in order for the problem to be well-posed. This is easy to check using the vector triple product, as ja72's answer shows.
Now, how does one get this using geometric algebra? There are several good introductions to GA online, so I won't write a new one here, but I'll provide some links in the end of the post. Now, assuming the basics are understood, we can immediately translate the problem in terms of the wedge product and the dual, using the relation
$$
a\times b  = a\wedge b I^{-1},
$$
where $I$ is the pseudoscalar in 3D space, and $I^{-1} = -I$ is its inverse with respect to the geometric product. This gives:
$$
a \wedge b = c I.
$$
The inner product product of $a$ and $b$ is some real number, say $a \cdot b = \alpha$. Let us add this to the wedge product to get
$$
a\cdot b + a\wedge b = ab = \alpha + cI,
$$
where the first identity is a fundamental formula in GA concerning the products of vectors.
Since vectors in GA have an inverse with respect to the geometric product, we can multiply from the right with $b^{-1} = \frac{b}{b^2}$ to get
$$
a = \left(\alpha + c I\right)b^{-1} = \frac{1}{b^2}\left(\alpha b + cb I\right).
$$
The fact that $b$ and $c$ must be orthogonal appears here in the form that if they are not, then $cb$ will have a three-vector component, and $a$ won't be a vector. It was of course also apparent in the first equation we wrote, since the dual of a vector in three dimensions is always a bivector orthogonal to the vector itself.
The previous formula is already the answer, but let us translate it back to the cross product form to get
$$
a = \frac{1}{b^2}\left(\alpha b + c\wedge b I^{-1} I I\right) = \frac{1}{b^2}\left(\alpha b - c\times b\right),
$$
where we inserted $I^{-1} I  = 1$ to the second term to get the cross product to appear, and used $I^2 = -1$.
If this got you interested in learning GA, the wikipedia article is not a bad place to start. Here some more links, though which of them are most useful depend on what's your mathematical background:

Imaginary numbers are not real
Lecture notes for a course on GA
A slightly more mathematical, but thorough, introduction
Geometric algebra for physicists

Google will find a lot more sources, which of them are best for you depends on your starting level, as I mentioned.


CLI Commands For Half-Open TCP Connections

Question: I have an HP ProCurve 2910al (J9146A) and I am being requested to drop connections or timeout connections with half-open TCP connections. I am having trouble finding commands or even understanding what half-open TCP connections are. My ports on the switch are set with port-security to specific MAC addresses. What commands can I use on my switch to drop or timeout half-open TCP connections?
Comment: That is not something you do on a switch. The switch will be ignorant about one side or the other of the TCP connection crashing or resetting. This is something normally handled in the hosts, and there are some firewalls that can deal with the situation by timing out a TCP connection.
Answer: Half-open TCP connections are connections that have not completed the three-way handshake (yet). For inbound connections, a SYN packet has been reveceived without an answer to the SYN/ACK reply.
As a layer-3 switch, the 2910al is a stateless router. Therefore it has no knowledge about half-open or completed connections that is has routed (or even switched).
If you want to defend the switch itself against DoS attacks you should move the management to a VLAN that normal users can't connect on. Additionally, you can use ACLs to deny unwanted packets as soon as they enter an edge/access port. Furthermore, you might want to disable the web interface if it's being attacked.
If you post the (sanitized) configuration and a better description of the actual problem we can provide more detailed help.
Comment: He started a discussion on [chat]. I gave him the part of the RFC, and explained that he needs a device like a firewall that maintains TCP state.
Comment: @RonMaupin is right. He gave me some understanding and I have enacted stronger Port Security and authentication which should help. But since we are using this as a Layer 2 switch without a Layer 3 device this requirement is a moot point. But this answer explains the understanding a lot better. Thanks.


What are the ports used by Magicka Wizards War?

Question: I'm playing behind a proxy and would like to know which ports to open in order to be able to play Magicka Wizards War (and not Magicka).
Answer: It seems that Magicka: Wizards War uses random ports from my own testing.
I tested it several times, and the result showed that it listened on port 15303, 15582, 16167, 17393, 17521 respectively in the tests.
It also used port 54254, 64594, 56102, 55128, 58629  for UDP respectively in the tests.
Therefore I suspect that this game will listen on a range of random ports and use a range of random port for UDP,  but I cannot be sure for the actual range. I will update this answer when I get more information.
Reference:
Ports used for QoS???????????
Required Ports for Steam
Comment: I'll tell you if it is enough, but it will depend on my house IT department :]


Touchscreen Setting 14.04

Question: So I installed 14.04 on an Asus Q200E with touch screen. Previously I had 12.04 and did a new clean install.  I was looking forward to better touch screen support. Touchscreen works better, no multitouch support, and I can't find any settings for it.  Also when the computer suspends and resumes touchscreen doesn't work unless I logout/ login.  Where can I find settings for touchscreen?  and is there a command line way to reboot the touchscreen when it stops working?
Answer: I'm not terribly sure about multitouch, but tablet and touchscreen can be config'd under Settings > Mouse and Touchpad, and then by selecting your touch device from the drop down menu. In mine, I can select "Serial Wacom Tablet touch" and then select the "Tablet" tab below, which allows me to configure the tracking and rotation.

Touchscreen Setting 14.04


Periodic ground state 1-dim ising model

Question: Good evening!
I'm at the beginning of my study about the Ising model and it has been proposed to me this problem:
Find all periodic ground-state configuration for the following one-dimensional Ising model of interacting spins, $s_i=+1$ or $ -1 $
$$
H=-\sum_{i\in\mathbb{Z}} (s_{i}s_{i+1}-s_{i}s_{i+2}-4s_{i}s_{i+3})
$$
Actually, I don't know how to procede. I know that the ground states, by definition, are the configuration of minimal energy. But then, is this possible to compute these configuration for this specific model in an explicit way?
I hope that someone could give me a hint, because I think that I'm a little bit confused..
Thank you very much!
Answer: The state with minimal energy will be an alteration of +1 and -1 spins. The reason is that the 1-4 interactions will dominate the rest. Each spin in your system will interact with 6 others. Even though 1-2 (neighbours) and 1-3 interactions will be unfavourable in the alternating sequence, two favourable 1-4 interactions with the weight -4 will have more impact.
You can probably make this more rigorous by showing that flipping a single spin or creating a domain with different alternation will require positive energy.
Hope this helps.

Periodic ground state 1-dim ising model


Is Romans 1 an ad-hominem attack on Atheists?

Question: From this question Contention by @MarcGravell: The Paul quote is very apt - but does it not strike you as a huge ad-hominem? i.e. because they have a different position, let's demonize them and invent insults ("fools", "foolish", "wickedness"). If a person today answered like that here on SE, we would not accept it as a constructive answer (or at least, without qualifying those claims)... just saying!
Comment: I can't decide whether this is a main site or meta site question. (Actually it might be best on BH.SE)
Comment: In any event, if it was a pointvalue question, I want to let Mark Gravell get the points for it.  I like it, but it will solicit debate and opinion :)
Comment: Where are you quoting this from?
Comment: I've never seen this type of discussion on SE - how does the format work?  Does it take place in comments, answer edits, separate comments, etc?
Comment: @eric this is the first time we've moved it to meta. I think we're going to find out. I tried to break out some of the arguments into answers.
Comment: See also my comment on Eric's answer - it contains a direct example of an attack as a central part of the argument.
Comment: Just for the record: I'm not fussy about the words "ad hominem" - if "character assassination" would be more acceptable, that's fine too.
Answer: Answer from @Eric: @MarcGravell, while it may be harsh or offensive, that does not imply that it is an ad hominem argument. He is not calling them fools, or wicked in order to argue that God should be acknowledged. Rather, he is arguing that God should be acknowledged because God had made it plain. Calling these people fools was not a point in this argument - it was the consequence of the argument he made. In other words, he is arguing that (A) "God made it plain" => (B) "He should be acknowledged" => (C) "They did not acknowledge" => (D) "They are fools". He is not arguing (D) => (C) => (B). – Eric 3 hours ago
Comment: Which is actually a good point: *ad hominem* != *insult*.
Comment: @TRiG if the insult is purely about the position, not the argument, and only serves to try to weaken their position by character assassination?
Comment: @Marc. Then you're on trickier ground. Perhaps that is an ad hom. I'm not sure.
Comment: @Marc. On reflection, I think Paul is [poisoning the well](http://en.wikipedia.org/wiki/Poisoning_the_well).
Comment: @Trig that will do nicely :)
Answer: I indeed said it was ad-hominem, but I didn't say it was against atheists specifically. Actually, that text applies equally to every non-Christian, or indeed anyone who disagrees (it was inferred, not by me, that the article might also apply to, for example, homosexual Christians - meaning Christians who do not tow the party line).
It is indeed ad-hominem, because starting from an unfounded assertion (there is no empirical proof of any God, so it is not unreasonable to choose not to believe in Him/Her/Them, whichever you choose), it pre-supposes, attacks, and derides (without any evidence) the nature of the people who it targets. It does not discuss their reasons for their not agreeing with the assertion, it merely demonises and insults those who don't agree. The person, not the argument. Ad hominem.
Comment: Again, from my point of view, its an ad-hominem attack against Christians.  Those who knew God chose not to glorify him as God, therefore bad, bad, bad....
Comment: @Affable I read :18-21 more as people who know of God, either through hearing it, or "from their hearts", but who do not accept them. The way I read :18-21 it is not limited to Christians. But that doesn't change that the text attacks the person, rather than attempting to defend/strengthen the position
Comment: So, one of the theories of what Romans is a single extended argument of divine intervention into the natural law. As one who preaches, I'll tell you that in my opening, I will usually be more provocative, if only to engage the hearer. That may be Paul's motivation, then move to logical argument in the rest of the book. The good Lord knows its a pretty extended argument.
Answer: My position is as @AffableGeek posted here.
@MarcGravell has responded:

It is indeed ad-hominem, because starting from an unfounded assertion (there is no empirical proof of any God, so it is not unreasonable to choose not to believe in Him/Her/Them, whichever you choose), it pre-supposes, attacks, and derides (without any evidence) the nature of the people who it targets. It does not discuss their reasons for their not agreeing with the assertion, it merely demonises and insults those who don't agree. The person, not the argument. Ad hominem.

Whether Paul's calling these people fools is unfounded is a separate issue.  Whether there is empirical "proof" of God is also a separate issue.  Paul's argument cannot be ad hominem, because he doesn't use these people's "foolishness" in his line of argumentation.
I think perhaps our disconnect is due to a disagreement on the meaning of ad hominem.  An insult is not in itself ad hominem.  Even an unfounded insult, which you argue is the case here, is not in itself ad hominem.
An ad hominem argument uses an insult (or characteristic of the opponent) as reasoning for the argument.  That is why it is a fallacy - Because, of course, the characteristics of the opponent have no actual bearing on the argument itself.
For example, if I were to argue that:

Dogs are so great.  They learn commands really well.  Chris doesn't like dogs - what an idiot for missing out on them.

I would not be committing ad hominem.  Now, I don't really have any grounds for calling Chris an idiot, but since I'm not using his idiocy to argue for dogs' greatness, no ad hominem. (Note: I'm not here to say whether or not Paul had grounds for calling these people fools.  I'm only trying to demonstrate that it's irrelevant to the ad hominem discussion)

Cats are so retarded.  Chris says they're great, but he doesn't like dogs, so what does he know?

Now I've committed an ad hominem.  I'm directly using a quality about Chris (his not liking dogs) to defend my argument against cats.  That's fallacious, because whether Chris likes dogs or not has no bearing on cat retardation.
That is not what we have here.  Whether the basis of Paul calling these people fools is founded or unfounded is irrelevant, because his calling them fools is its own end, and not a point in his line of reasoning.
Comment: The implication in Paul is circular, IMO; the foolishness is directly tied to their non-acceptance, to the point where it could be described as causal. As another example, "and wickedness of people, who suppress the truth **by their wickedness**" - (emphasis mine) that is using the attack *as a core part of the argument*
Comment: Right, "suppress the truth by their wickedness" implies causality - but not the right kind of causality.  The causal connection Paul makes is that they did not believe **because of** their wickedness.  But that is not the causality that an ad hominem argument would use.  His argument, that God should be acknowledged, is not based on the claim of these people's wickedness, or of the people's subsequent disbelief.  His argument is based on God's invisible qualities... having been clearly seen.
Answer: Calling someone a fool is not an attack on their character.  It is a spiritual work of mercy.  A living out of what you're supposed to do in response to the 5th commandment (do not kill). A fool, in this sense, is someone in danger of spiritual death. If you were rollerskating near the edge of something:

You might be apt to shout, "you fool!"
If you were teetering on the edge of damnation, you might as well be apt to shout, "you fool!"
Comment: And if the "edge of damnation" is entirely, er, "debatable", and only exists to the person shouting "fool"? I'm reminded of the tin-foil hat-wearers who think that it is foolish to let the government steal their thoughts. If the person shouting "fool" can't show an actual real risk, I wonder where the fool lies...
Comment: Yeah, and if Paul was wrong then we're the fools,  it's not like he didn't acknowledge that. How does one properly deny the risk involved Pascal's wager (that if one is wrong about God they lose everything) again?
Comment: Paul also made the case himself, that if we are wrong about Christ,  "we are of all people most to be pitied." (1 Corinthians 15:19)
Comment: "Calling someone a fool is not an attack on their character. It is a spiritual work of mercy." Seriously, do you have *any idea* how arrogant you sound?
Comment: Pascal, when evaluating the "if I'm wrong" case, fails to give any meaning to living a life based on untruths (remember, we're discussing the "if I'm wrong" case), and the injustices and harm imparted, and indeed time and resources wasted. This is a very real cost; indeed, in the "if I'm wrong" case it is only the things in this life that matter (since no other scenarios are presented)
Comment: @Trig from an academic point of view, Peter isn't actually very far off. The word fool has changed in it's connotation over time. Remember, from Proverbs, a fool is simply someone who will not listen to wisdom. Grant you, it isn't a terribly pleasant thing to be called, but using that definition, in the context of Romans 1, fool is exactly right - someone who will not listen to wisdom. That person might have a perfectly valid reason for rejecting Eason, as defined by Paul in this case, but the word fits it's biblical connotation.
Comment: If Paul is simply setting up an argument, then the rest of the book will simply seek to substantiate this charge.
Comment: @Trig, it may well be that I am a resounding gong.  But the spiritual works of mercy are just a set of good works one can do in response to the commandments and the beatitudes. [Check it out if you don't believe me](http://www.newadvent.org/cathen/10198d.htm).
Comment: Actually, before calling someone a fool you might want to see Matthew 5:22
Comment: @marc glad to see you're reading the Bible!
Comment: In any event fool here is meant the way Gandalf says "fly you fools" or "fool of a Took".  In Matt 5:22 it's using fool in a deragatory manner which is the dangerous thing. Is that what you were asking in the first place, whether St. Paul was using "fool" in a deragatory manner?
Comment: really struggling to see the difference here... not sure there's enough information to make that assertion. I guess the bible needs more smilies, i.e. "fool!" vs "fool ;p"


Is the Intersection Operation Commutative?

Question: In map overlay, is intersection of map layers a commutative operation ie layer_A intersection layer_B = layer_B intersection layer_A?
If layer A is a square and layer B is a triangle. In this case, (A intersectn B) == (B intersectn A) ?
Answer: Just like set intersection, geometric intersection (which is essentially an intersection on two sets with spatially defined bounds) is both commutative and associative, e.g. (A ∩ B) ∩ C = A ∩ (B ∩ C) = (C ∩ B) ∩ A = C ∩ (B ∩ A).
In practice, software often uses the order of inputs to determine how attributes are associated with the output; but the spatial output geometry should still be the same regardless of input order.
Also be aware that your output will depend on which coordinate system and projection, if any, you use to carry out the operation. While this will not change the commutative and associate properties, order and grouping might be used to select the projection used for the operation(s).
Comment: I haven't tried it lately, but with ArcGIS I recall that that the order of arguments for intersect matters  if the XY domain (xy precision) of the layers involved differ - even though the spatial references were the same.
Answer: Hope this figure is explicit enough :

From : http://www.gaia-gis.it/spatialite/spatialite-tutorial-2.3.1.html
Comment: thanks for the reply, so I should assume A.B = B.A where A and B are two different vector data map layers?
Comment: the equality you mentionned is correct, see also blord-castillo's answer.
Answer: Mmmm. I too thought it obvious that A ∩ B = B ∩ A, but then Kirk's comment got me thinking.
So here's a theory. Feel free to shoot it down in flames!
In this scenario there are two polygons, A (red) and B (blue). The red dots represent the smallest grid precision:

According to my calculations, they intersect here:

Notice how the intersection point snaps to the nearest grid, because that's the smallest precision allowed. In this case the order doesn't matter, and A ∩ B = B ∩ A
Now introduce polygon C (yellow):

The intersection of (A ∩ B) ∩ C is as follows:

And that's because the nearest grid point to the intersection of A and B is as already shown, and overlaid with C is can give that result (my rough sketch is not exactly square so it may not look obvious at a glance). However, (A ∩ C) ∩ B gives this:

That's because the nearest grid to the intersection of A and C causes a different shape for the intersection with B.
So: I would argue that there is no difference with just two polygons, but there could be differences with three or more. With a large precision the differences would be tiny, but I believe they could exist.
Does that look correct, or can anyone pick holes in the concept?!?!?!
Comment: Or to take that to a different context, consider a computer that stores numbers only out to 5 decimal places. 4 * 0.1 * 0.00005 should be 0.00002 in theory, whether done as (4 * 0.1) * 0.00005 or as (0.1 * 0.00005) * 4. But when carried on on this computer, (4 * 0.1) * 0.00005 = 0.4 * 0.00005 = 0.00002 but (0.1 * 0.00005) * 4 = 0.00001 * 4 = 0.00004 (or it is equal to 0.00000 * 4 = 0 depending on how rounding is handled). The result would imply that multiplication is not associative or commutative, but the result is really just an artifact of the computation method.
Comment: That would still be a software dependent issue though. You could just as easily store the result as a vector function intermediate until all intersections are completed and then convert the vector input to the spatial precision when done as well. The actual theory behind the operation has the operation associative and commutative.


How can I access owncloud files by the owncloud server?

Question: I want to see owncloud files by again the owncloud server machine. Do I need tot install client program to the server machine anyway or is there any other method to reach the owncloud files in the server?
Comment: Owncloud has a web interface.
Answer: You can mount the DAV share trough davfs2 that provided a safe read/write access to files without using the owncloud desktop client (that make a useless, in this case, local copy of all files).
To do this you must install the packet davfs2 with
apt-get install davfs2
In Debian based systems, or
yum install davfs2
in RedHat Based systems.
Then you must edit the file /etc/davfs2/secrets adding at the end a line with your login credentials, like:
owncloud.example.org/owncloud/remote.php/webdav
And now you are able to mount the share as a normal filesystem with the mount command:
mount -t davfs owncloud.example.org/owncloud/remote.php/webdav /mnt/
More options (like permit mount to an unprivileged user) are available, owncloud doc has a good step-by-step guide to do this:
https://doc.owncloud.org/server/7.0/user_manual/files/files.html#creating-webdav-mounts-on-the-linux-command-line
It's true that you can directly access your file in the data/ dir but it's not the cleanest way (especially if you want edit/add/delete them).
Comment: link-only answers are frowned upon and are not really that helpful.
Comment: @Ramhound sorry, I'm new here and maybe I misunderstood the best practices. The link point to a step-by-step guide to mount an owncloud share with davfs2, so I simply avoided to fill the page with a log copy-paste. Maybe best practices say a different thing? Thanks
Comment: Take a look at the help center so you don't make preventable mistakes.  Before submitting an answer to an existing age question, be sure the answer is absolutely exceptional, because I personally hold new answers to old questions to a higher standard then answers to new questions.  Be sure the answer to this existing question, is adding something unique, which hasn't already been said by somebody else.  Just adding your comments isn't helpful, if you want to add comments to those questions, submit comments.
Comment: @Ramhound reading again my answer it looks too a "just search somewhere on doc", so I edited to clarify. About the "old question" I noticed the age only later (I found it jumping around on open questions about owncloud). Finally, I think that the answer is pertinent and provide a proper way to mount owncloud share with safe read/write support without using the desktop client, as originally asked (I don't know if you looked in technical details). Anyway thanks for clarifications :)
Comment: When an answer contains a link, without any quote blocks, and it's not a download I make that comment.  "Step by Step guide" but that guide doesn't exist here at Superuser
Comment: So the problem is that it is an external link to official owncloud doc? A one-hundred lines of quote is better in these cases?
Comment: provide a summary.  It's 9 steps.... That's like 25 lines at most
Comment: Updated my answer
Answer: just access the web-interface with this adress/link:
http://localhost/owncloud or eventual https://localhost/owncloud
if you want to "take a look behind the scenes" (or haven't installed a desktop environment) you can start your file-manager and look for /var/www/owncloud/data/"username" (for the case you are running an apache-server)!
Answer: use ssh to access the server, find the install directory and have fun with the files.
if a apache is installed you can find the the directory in the apache conf but normaly it should be under /var/www/
you can also use winscp to acces the server
Comment: This is plain false and dangerous. You shouldn't even have read permissions to ownclouds datafolder, and Ieven if youd do and change anything, the application will not be aware of it, the database entries will not be updated etc.
Comment: true , it is dangerous to modify the owncloud files. I would leave them as they are.
Answer: No problem, you can open a terminal from the graphical interface of the server if you have physical access to it and run nautilus with sudo permissions and then navigate to the directory where you have the filesystem mounted.
Answer: If you use a apache the main directory for owncloud is
/var/www/html or /var/www/html/owcloud
There are store all files on your owncloud server.


How can I make Github for Windows use my real name for commits?

Question: Normally, I use the email address and my real name for git commits. However, the Github for Windows client defaults to using the Github username for the commit author info. Because of that, I have commits with both names mixed up in the repository now. I know how to rewrite history to fix that, but is there a way to make the client use my real name by default? This issue could be avoided in the future then.
Answer: Presumably it simply uses git's own mechanism for saving usernames. You can change this from the Git Shell:
git config --global user.name "YOUR NAME"

In fact, that command comes from GitHub's own help docs.
Answer: As Bob said in his answer, GitHub for Windows will use the name you've configured in Git for the author on the commit.  The GitHub for Windows UI allows you to configure both your name and email address via the settings.  Click on the "Tools & Options" button and select "Options...".  From the options screen, under "Configure git," you can change your name and email address.


Why do some physicists think the universe could be infinite?

Question: The deeper we look into space, the more primitive the structures are. Since we can see really primitive galaxies like Quasars, it's reasonable to think that there are even more primitive structures beyond Quasars, and eventually if you look deep enough, there would be nothing to see, because no structures, or even atoms, have formed so far in the past. The question of whether the universe is finite or infinite seems to be answerable this way, because clearly the universe must be finite if there is a radius beyond which nothing exists. So why is this question still not settled?
Comment: Possible duplicates: http://physics.stackexchange.com/q/24017/2451 , http://physics.stackexchange.com/q/141835/2451 and links therein.
Comment: It's too simple to post as an answer, but I think you're overlooking the scale invariance of relativistic theories:  Variations in scale could be consistent and endless, as well as resulting in their practical imperceptibility.  The relevant Wiki is "infinite divisibility".
Answer: The reason why the question is still unresolved is partly given by what you said. The further we look, the further back in time we go, until we get to a point where we see the beginning of the universe (strictly speaking we can only see as far back as the cosmic background radiation allows us to). This limits the distance we can see. But this does not mean the universe only extends to this distance. Imagine for a moment that light propagated at infinite speed. Then we would have been able to see to the end of the universe. So the limit of what we can see is set by the finite speed of light and not by actual size of the universe.
Answer: This discussion will remain up in the air forever because the answer is abstract and uncertain as the question is about being infinite. Infinity is something beyond the grasp of our mind.
However, as a tool for practical problems we can assume the universe to be infinite. For example, we discuss infinite rods and sheets in electrostatics which aren't actually infinite but are infinite in the way we define the situations. For an infinite rod, for instance, if we are very close to the rod as compared to the rod itself then we can use the approximation that the rod is infinite (as the upper and lower end of rod are not in our field of view from that close distance). Thus we can see that infinity is something to be defined relative to some other thing.
As we have no known way of getting to the boundary of universe which is probably beyond the arena in which microwave background allows us to see, we can say for all practical purposes that the universe is infinite.
Answer: Physicists are of the opinion that universe is infinite because they have figured out that the galaxies and all parts of the universe are moving far apart from each other and this movement is accelerating as well. This also leads scientists to think of a Big-Bang like beginning for the universe.


How do I stop a DataGridView from automatically selecting a row?

Question: I have a DataGridView control in a TabPage, and I listen for the SelectionChanged event.  When the TabPage is selected, the DataGridView selects the first row and fires the SelectionChanged event.  How can I stop it from automatically selecting a row?
Answer: I can think of two ways of working around this, If you know the event always fires, Have a bool flag that is set on the first selection, then only perform the rest of your SelectionChanged code.
The other way is to have a hidden control that is the first TabStop for the TabPage and hence is the first control to get focus (I say this without having tested any this of course, just my two cents).
Answer: Override the function "OnEnter" of the TabPage.
Call the function "ClearSelecton" of the DataGridView within this function.


Motor acting as a generator with backfeed

Question: 12v DC automotive question.  I replaced the engine-driven clutch fan with an electric radiator fan, controlled by thermostat and relay.  I included an LED in the vehicle to show when the fan is ON.  Everything works fine most of the time, but I find that when vehicle speed gets to around 55 MPH the LED is coming on even though the engine temp should not be triggering the thermostat.  I'm convinced that the fan is being driven to turn (freewheeling) by the relative air at speed and the fan motor is generating current back into the system.  Is there any ill effect of letting this condition persist, e.g., reduced fan life due to the heat by-product of the generated current, damage to other electrical components.  If so I could add a switch to control it, or a diode but I understand a diode will limit the voltage to the fan when running in normal mode.  Thanks.
Answer: If the relay disconnects power from the fan, then the fan isn't backfeeding anything except the LED that you placed across it.
Comment: If there's a spare contact on the relay, you could route the motor output to another LED labelled "Speed limit exceeded".
Comment: If there's a spare (normally closed) contact, he could have it short across the motor and effectively have a brake.  Unless it's a brushless motor, that is.
Answer: You could also add a plunger that retracts when power is applied. that way your fan bearings would not be worn out by freewheeling. However you would also want to include a brake circuit to stop the fan prior to re-engaging the plunger. But as already mentioned if the relay is disconnecting the fan from the circuit you will not have any ill effects apart from shortening the life of the fan and possibly generating EMI.