Linux distribution geared towards developers

Question: I am looking for the best flavor of Linux that would appeal to the developer's side of me. I am a lover of open source and use several different languages.
Is there such a thing as a Linux geared towards developers?
Comment: You should specify a bit what you mean - Developers have very strong (and often opposing) views of what constitutes a developer-friendly distro.
Comment: Open discussions are not appropriate to post here.
Comment: @l0b0: Developers need a big selection of up-to-date packages. Updating packages manually because they are too old, not vanilla enough or just not in the distro's repository is a waste of time. End users usually don't care if the up-to-date libxyz-dev package is inside the repository.
Comment: have a look at FreeBSD
Answer: In practice the distros all use much the same development tool chain, so they don't really differ significantly as a platform for general development work.  Some do, however, have specific advantages that may be relevant to certain types of development work:

The commercial distros (RHEL, SLES) have the best support from third-party closed source vendors.  If you want to work with (say) Oracle you might be better off with one of these, although Oracle can be made to work with most distros if you install the right libraries.  CentOS is compiled from RHEL sources and will play nicely with most if not all commercial software built for RHEL.
If you want to tinker, you might try Linux From Scratch.  It's quite a good tutorial on how a linux distribution hangs together.
If you want something for which just about everything that is or was ever open-source is available from repositories, then a Debian based distro (either Debian or Ubuntu) may be a win.  There's a reason Canonical picked .deb to use as the package management system for Ubuntu.
If you want to tune everything to the n-th degree then Gentoo lets you rebuild your entire system for your specific processor architecture.
If you want a 'traditional unix' experience then you could try Slackware or FreeBSD (which is not a Linux distro but might be of interest to the OP).  Also, the BSD family are particularly strong in networking so they may offer advantages over Linux to developers working in this field.

Of those, I've used CentOS, Debian, Fedora, Ubuntu, Slackware and FreeBSD at various times in the past, plus a few others (Vector, SLS, Yggdrasil and assorted versions of Redhat from about 4.0 onwards).  As a 'unix' development environment they all offered the tools of the era and could have been used for development work with the bundled tooling or by downloading and building whatever else you needed.
Unix was once described as an IDE masquerading as an operating system, or words to that effect.  Any unix or linux variant can give you the unix developer experience if you want that.  At one point I didn't really care much for the environment.  I really just used the window manager to open xterm windows and start a few apps; everything else was pretty much done from the command line.  Most varieties of unix or linux can do that.
If you're into C then vim or emacs with ctags, make and gcc works pretty well; you can use gdb with or without a frontend.  This tool chain also provides good support for languages such as perl or python and comes with a rich ecosystem of support from third party tools.
For a more GUI-centric workflow it really comes down to a personal choice of window manager, desktop environment and development tools.  If you're into Java then Eclipse and netbeans have builds on most major distros.  Various conventional IDEs exist with support for C/C++, perl, python and other scripting languages.  These can be made to work on most if not all Linux distros.  Java is only supported on BSD through 3rd party ports so you're probably better off with linux if you're working with that.
Comment: IMHO only bullet points one and three are relevant to developers. Tuning or Unix experience are only interesting for power users and sys admins. They lead to incompatibilities (Unix) and unpredictable instabilities (Tuning), both poison for developers.
Comment: The BSDs and Solaris are sorely lacking in hardware support, and after having had an advantage of sorts in networking the BSDs have lost out on that end too.
Comment: Of course FreeBSD is not a Linux system.  That may not matter for the OP's purposes.  Note that there are several other BSD distributions (OpenBSD, NetBSD, and I've probably missed some).  There's also a free version of Solaris if you're into that kind of thing.
Comment: No, it isn't, and I'm guessing that it may or may not matter for much the same reasons.  I picked that one because most of the other BSD distros are pretty specialised, perhaps witht he exception of Dragonfly or PC-BSD.  FreeBSD is about the most mainstream of the BSDs, I guess.
Answer:
Is there such a thing as a Linux geared towards developers?

Yes. It's called Linux.
Fedora (or any Red Hat derivative) is as good as any Debian, Slackware, Gentoo or whatever. Seriously, you can develop with any major distribution, it's a silly question to ask for a "developer oriented" Linux.
It's also silly to say that any of these distros is better than the others for developers. It just isn't serious.
This question really begs for arguments.
Comment: It's silly to say that it's a silly question to ask for a "developer oriented" Linux unless you provide good arguments for *why* it's silly.
Comment: You really need to qualify "Fedora is as good as any Debian, Slackware...". Surely there's must be reasons why there are different distros, and that means they can't be equally good in any given task for different people.
Comment: Doing my work I need stable environment. Considering this eg. Fedora and Ubuntu are far from stable and I don't recommend them. You can say "Linux is good for developers" to Windows user because it's general state. When you're talking to Linux users they probably are interested in more particular things which would improve their efficiency.
Comment: In fairness, juaco is right. Linux is good for developers, period.
Comment: @Tshepang:You're right, they aren't equally good "for any given task" _except_ for development. For other tasks they do sometimes show differences, but for dev'ing, all major distros are equally good.
Comment: @Joe: I'm talking about the major distros, each and every one of them have the same programming tools. Including, but not limited to, the gcc collection.
Comment: That is far from true. Yes it is easy to compile a program on any given linux but that is because of gcc. For clarification on what I mean see my responses.
Answer: There's more and more different flavors in Linux distros–for instance there are distros like Qimo or DoudouLinux which are oriented for children.
Of course you can change them to fit your needs (we're talking about Linux, right :]), but still, you'll waste a great amount of time.
Some will argue that it's a great way to learn new things. However, you will have to take some time to dig in the distro and tune stuff anyway, it's inevitable with any distro.
But the most important thing is the packages.
Some brings you fresh ones (e.g: Arch) and some others very stable ones (e.g: Debian).
The documentation varies also a lot, as for hardware support (drivers, drivers, drivers!).
Considering these 3 points (packages, documentation, drivers) and your own skills, you should take some time to discover some mainstream distros.
A good start could be here: http://distrowatch.com/
Comment: I did say **major distributions** ie. mainstream, to refer to the fact that there aren't big differences between these when it comes to development. I'm not referring to niche distros.
Answer: I've tried out quite a few distributions because I really enjoy doing so.
I'm a developer and I've also wondered about a good Linux for developers, and in my experience there aren't any Linux distributions geared specifically for developers.
The reason is that as a developer, not only will you be able to customize any distro to suit your needs, but you'll definitively need to know how to do such customizing.
So basically if you're unfamiliar with Linux:
1) Debian, because a lot of production web servers are running Debian, so it's probably a good idea to get to know how Debian machines are organized. The good thing about Debian is that since it's definitively the most widely used Linux (including it's derivatives such as Ubuntu) the support, community and number of pre-compiled packages available is extremely extensive. The bad thing about Debian is that it's geared towards being a stable production environment and as such rarely offers you the latest bleeding-edge stuff that you might want to try out as developer.
2) Arch-Linux (ArchBang actually) is my current favorite for 3 reasons:
- It doesn't provide much in the way of easy one-click install and configure stuff but has a great tutorial to help you get everything set up like you want, this approach allows you to learn a lot about how things work in the background and means that by te time you've got everything set up properly you'll be feeling pretty damn comfortable using a Linux/Unix system.
- It's rolling release, wich means you'll never have to download the new version and reinstall everything, you just update the system and Voila !.
- It tries to implement all the lastest bleeding edge stuff so you'll always be keeping on top of new improvements to the software, and as a developer that's really appreciable.
-Oh and it has a great community too.
But anyway it basically is up to you to try out a few stuff and decide what works best for you, what I can garanty is that no matter wich Linux you end up tying there's always a way to configure/customize stuff to your liking, so the big deal is learning how to do that customizing, and then you choose something that's already pre-configured as close as possible to what you want to end up with.
Answer: Fedora is an early adopter of new technologies, allowing you to experiment and develop with them months before they're available in most other distros. It supports many programming languages and libraries out of the box, and makes it relatively easy to add to your system any that may be missing. It has a pure open-source philosophy, choosing to allow third parties to provide packages for features that are contrary to that. Just don't call it "Fedora Core" (it lost the "Core" after Core and Extras merged for Fedora 7).
Comment: @IgnacioVazquez-Abrams: You should also not correlate *uses newer technologies* with *better to develop on*. Anyways, the question is not specific enough... it depends on what you are developing. I'd bet most of the world's development relies on not-bleeding edge technology. OTOH, Fedora is the distro I'd suggest if one wanted to do [GNOME development](http://unix.stackexchange.com/q/8771/8809#8809), same as SuSE for Mono and KDE development (this based on the fact that SuSE is the initial funders of Mono project and is among the few major distros to embrace KDE as default desktop.
Comment: Who called it Fedora Core?
Comment: Plenty of people. For years.
Comment: @IgnacioVazquez-Abrams what about gentoo and archlinux
Comment: I can't tell you about distros I don't use. But certainly don't try to correlate "builds from source" with "good for programming".
Comment: @IgnacioVazquez-Abrams: It sounded like you were correcting someone here who called it Fedora Core.
Answer: I think, based on my own experience and the answers here, you're looking more for a suite of applications and tools that will make development easier and more practical.
The cool thing about Linux is that any distribution is very easy to customize. I would recommend you find a list of software you use most often while developing and make a large tarball which you can bring from computer to computer (if you switch workspaces a lot).
Answer: For Java/Eclipse development, consider Debian over Ubuntu/Linux Mint (and possibly even 32bit over 64bit).
Background: I have been doing some Java / Eclipse RCP* development and have been using Ubuntu and later Linux Mint, but have run into all kinds of annoying bugs, either related to instabilities in the desktop environment (Cinnamon on Linux Mint), or a somewhat complicated procedure to install Sun Java6 JDK (which is used by our project ... Ubuntu/Linux Mint ships only with OpenJDK in their repos).
I recently fired up Debian 6 Squeeze in a virtual machine, and realized how these things were working much better. Installing the Sun Java only requires adding the "non-free" keyword after the main repository string in /etc/apt/sources.list and then installing via apt-get, and the (Gnome2) desktop shipped with it is also much more stable than the Gnome3/Unity/Cinnamon alternatives in Ubuntu/LinuxMint.
[*] Eclipse RCP means that you use Eclipse not only as a GUI but also as a library for building your own GUI, sort of.
Answer: Ubuntu is great, seriously.
They have all the packages, up-to-date and easy to install. Use the default configuration (= Gnome) and you will spend most of your time programming and not configuring.
Installing the gcc compiler suite, make, autoconf etc. takes 5 minutes with a decent internet connection. Thirty more minutes and you have Ruby, Python, the Sun JVM and Eclipse ready-to-run.
Edit: Ubuntu delivers extra packages with debug symbols for a lot of libraries. Nice to have for C/C++ developers.
Comment: Your comments apply to nearly every other Linux distribution!
Comment: Interesting... http://www.go2linux.org/debian-ubuntu-centos-fedora-comparison and http://oswatershed.org/ (right column) Trust me, Ubuntu is developer's friend.
Answer: The answer is that there is not a good Linux for development enless you create one and no other linux really provide as much in this area as gentoo. You compile everything from source (something you should be frailer with to be a dev. The installation process teaches you more about the system than any other distro per-answering many questions you are going to have as you create applications.
The best part is you can pick what kind of programs you want to develop. If you want java install javac or gcj or both. Community support is like no other so if you have questions they will be answered or get you where you need to go to find the answer.
Every IDE you can think of is available to "emerge"/ install into gentoo. Though it is not incredibly easy to install or "simple" to understand, nether is programming and if you can not install a copy of gentoo, I would not want to run your programs on my machine. Most of the difficulties people have installing it are derived from a lack of fundamental Linux knowledge. I promise you will like it after you have everything setup the way you like it.
After you get it installed you can make a tar back up and put it on any computer that you have time to reconfigure a kernel for or use it restore when things get out of hand.


Is it legal to write a novel about people playing "League of Legends"?

Question: I was wondering if using trademarked items such as a bottle of "Pepsi", or a video game like "League of Legends" can make you vulnerable to lawsuits. I think so, but I am not sure, because I see a lot of media where products are often renamed into something similar like "Google" to "Poodle" and so on.
Answer: What you're talking about here is trademark law. "Pepsi", "League of Legends", etc, are trademarks. It's completely legal to refer to someone else's trademark, as long as you use it properly. But there are two big catches.
Number 1: You can't use someone else's trademark as your own. You can say, "George liked to play League of Legends". But you can't make up your own game and call it "League of Legends".
Number 2: You can't use a trademark as a generic term. For example, Coca Cola company's lawyers used to go after anyone who used the word "coke" with a small "c" as a generic word for "cola". They had a good legal reason to do this: The courts have ruled that if a company does not vigorously defend their trademarks from generic use, that they can lose their exclusive legal rights to the name. "Escalator" used to be a trademark, but the company failed to protect it, and the courts ruled that it was now a generic term for a moving staircase, not the property of any one company.
Number 3: If you refer to a trademark, you are clearly identifying who you are talking about. And if you say anything negative about them, they could sue you for libel. If you just wrote, say, "George Googled the word 'aardvark' and quickly found the information he needed", I can't imagine that Google would object. They're probably happy when lots of people talk about their company in a generic or positive way. But if you write a story about companies invading people's privacy by collecting personal information, and the chief villain in your story is an evil company named "Google", you might be hearing from Google's lawyers.
(Those are the issues I can think of, anyway. They're might be others.)
Unless you really need to refer to a real trademark for your story to make sense, it just avoids trouble to use made-up trademarks.
Like if you're making a TV show and the hero looks something up on the Internet, maybe in real life he's use Google, but it's easy enough to have the computer screen on the TV show say "Frugle". The audience will still understand what's happening and you avoid any potential problem.
In your case, if you want to say that the characters play a video game, does it HAVE to be "League of Legends"? Would it hurt the story if you said that they like to play "Hall of Heroes" or some such made-up name instead? If for your story to make sense the reader has to know some crucial fact about League of Legends, well I think that's just a bad idea. What if a reader has never played the game? I don't know what percentage of the world's population has played this particular game, but I'm guessing it's fairly small. (Personally I've never heard of it before reading this post.) So to make the story work you'd have to explain anything about this game that is relevant to the story. At which point you could use a made up game and explain the same things just as well.
Of course I don't know what you have in mind to write. It may be that there's some very good reason for naming this specific game.
Comment: The reason you will frequently see the BBC, in particular, not use "real" trademarks in its TV shows is because [it violates their editorial policies](https://www.bbc.co.uk/editorialguidelines/guidelines/editorial-integrity/product-prominence), and not necessarily because of actual legal issues. Other TV studios use product placement freely and even get paid for doing it.
Comment: @Kevin If someone is paying you for product placement, presumably you have talked to them and they agree to your use of their name. They're not going to sue you. (Well, unless you violate the terms of the agreement.)
Comment: @Kevin A lot of times a TV show or movie will not use real brand or product names is because they want to be paid for product placement.  They don't want to give it away for free.
Comment: I can see the desire to use real names like "League of Legends" if you want to give the reader a feeling of being grounded in reality that just isn't the same if you make up a name - also, it's just a style that some people like to use. Stephen King comes to mind - he often uses real names, such as real car brands / models.
Comment: @colmde Sure, using real brand names that the reader is familiar with can give a certain feeling of reality to the story. Like saying the hero drank a Coke or drove a Ford. But I'd be careful about assuming the reader is familiar with any but the best known brands. "All my friends play League of Legends" is not at all the same as "Anyone who might read my book plays League of Legends". My father wrote a book where he made a reference to a certain store and apparently expected his readers to be familiar with it. I'd never heard of it. ...
Comment: ... I looked it up and I found that they have hundreds of stores all over Tennessee, where my father lives. But they don't have stores in other states, so for anyone who doesn't live or regularly visit Tennessee, they've probably never heard of it.


replacing parts for Oil leaks on mercedes 230 slk 2001 and time it takes

Question: How long should it take to replace a crankshaft seal and camshaft adjuster magnet on 2001 slk230 mercedes? And, wouldn"t you notice a oil pan gasket leak when you saw other 2 leaks?
Comment: A crankshaft seal replacement is a tough job, it requires the removal of the transmission to reach the seal
Comment: For those looking to close this, there is a definite (non-opinionated) answer to this question ... it's called "book hours". This is an on-topic question (at least that part of it). The other question is subjective, but is reasonable to answer in the affirmative. I don't have access to book hours ... hoping someone else does.
Answer:
wouldn"t you notice a oil pan gasket leak when you saw other 2 leaks

Unlikely. Heck, it's tough to pinpoint one oil leak sometimes. If other leak sources are leaking above the leak coming from the oil pan it would be impossible to say whether the leak was from the pan gasket or an above source. Sometimes the best way of going about this is to only fix the spot you know is leaking, clean old oil off, run it for a bit, and then recheck for leaks in other suspected places. It's a chore.
I'm working through this on an W211 E55 at the moment. Mercedes can be leaky beasts.
Answer: Removal & Replacement on the camshaft adjuster magnet is 1 hour of labor. The front crankshaft oil seal is 2 hours. The rear crankshaft oil seal is 2.3 hours.


Sphere with surface charge density - why use Laplace's equation?

Question: I have a question where there is a grounded conducting sphere and inside that sphere is another sphere which is non-conducting and has a static surface charge density of $\sigma(\theta) = \sigma_0cos(\theta)$. If I want to find the electric potential inside the larger sphere, from looking at other questions I think I need to use Laplace's equation, but unsure why. I understand Laplace's equation is just a special case of Poisson's equation where $\rho$ = 0, and $\rho$ is the charge density. Here since we have a surface with surface charge density, isn't $\rho$ non zero? In general, in what scenarios is Laplace's equation used and when is Poisson's?
Answer: While $\rho$ is nonzero at the boundary of the region you're studying here, $\rho=0$ everywhere inside the region where you're trying to find the electric potential, namely in the region between the two spheres. Therefore the potential satisfies Laplace's equation everywhere in that region.
Poisson's equation would be useful in the instance where rather than having a surface charge density and looking for the electric potential outside of it, you were instead given a region with a specified volume charge density and asked for the electric displacement field ${\bf D}$ inside. Then there would be a charge density filling the space where you're looking for the solution, rather than just being present on the boundary.
Answer: You are in fact solving the Poisson's equation
$$\nabla^2\Phi=-\rho/\epsilon_0$$
But since it is a surface charge density, in differential form the $\rho$ becomes $\infty$.
The solution is to go back to the integral form and integrate across the surface, which reduces to matching boundary conditions inside and outside the sphere, both regions inside which you solve the Laplace's equation since there is no charge.
Answer: This configuration is very special.
I just wanted to tell you a beautiful way to solve this problem.
Please read this only after trying to solve the problem without integration.
You can treat this configuration as two uniformly charged solid spheres with equal and opposite charge density whose centers are a very small distance apart.
Then it becomes a classic example of -ve charge superimposed on +ve charge, and you will find that the field inside is constant. The proof is sufficiently easy. You can try it if you don't know it already.
I'm sorry if this is not what you asked, I just wanted to tell you.
Hope it helps.


Replacing Lighted Ceiling Fan w Fixed Light

Question: I just replaced a lighted ceiling fan with a fixed light fixture. My wall has two switches, one that controlled the fan and another that controlled the light. At the ceiling junction box, there was an off white wire, a black wire, a red wire, and the ground. My light fixture had black, white, and a ground wire. I connected the black to black, white to off white and the ground to ground. I capped the red. The light works fine when I turn it on and off but the light is now controlled by the switch which previously controlled the fan. That tells me the black wire in the junction box powered the fan previously and now sends power to the new light fixture. My question is can I keep it this way or should I connect the black fixture wire to the red junction box wire?
Answer: You explained it perfectly and yes, you can keep it that way or switch the black wire from the fixture to the red wire and cap the black. You would want the switch that's the easiest to find, in the dark, to control the light.
Comment: Thank you Jack!  I can now ensure my wife that I will not burn the house down. Very much appreciated!  And thanks for the quick reply.  Stay safe out there. Tim


PHP on IIS7 not showing pages

Question: I have a PHP website on a Windows 7 machine I'm working with and it cannot be viewed by any browser - IE, Chrome, Firefox. When navigating to the root of the website (default index.php) the browser reports it cannot find the address. Not a 404 error from the webserver, just as if it cannot resolve the name. Other websites in the same default web application that are also PHP work perfectly. I've aligned all folder permissions and everything else but this has got me stumped. I even went as far to create a new folder and throw in a test phpinfo() page and it worked. Copied this website's content to the new folder and it cannot find the index.php page. I checked all setting I know and can't seem to find what I'm missing. Anyone else encounter this issue? Remember the fix for it?
Comment: Could you please add to your post an example of a url that works and the one that doesn't ?
Answer: Something to try:
1) Make your phpinfo page again and verify that it is working.
2) copy/paste the content of the actual index.php file you want to use into your working phpinfo test page. (that is, open your working test page in a text editor and paste the actual page's text into it)
3) see if it works!
I had plenty of fun troubleshooting a few php pages a few years ago, it turned out the file I was working with had hidden symbols on line 1 that I couldn't see in the text editor I was using!
Good luck!

PHP on IIS7 not showing pages


How to solve a Stiffness matrix?

Question: I am quite new in this field. For my university I prepared a stiffness matrix to solve for a project group. This matrix consists of 450 equations with 450 unknows (it's a Matlab script) and I have the associated load vector $\{L\}$ of 450 rows. since I need to calculate the displacements would you advice me to simply do $\{x\} = [K]^{-1}  \{L\}$?
Comment: This is such a small problem that matlab's backslash operator is the way to go.
Comment: Just use any routine for solving linear systems, as inverting a matrix must be avoided. In MatLab, you have the backslash. Look the documentation on mathworkds, you'll find anything you need
Answer: As mentioned in the comments by Wolfgang Bangerth, for this problem you want to use the backslash operator, i.e.,
<code>u = K \ L;
</code>
In general, you don't want to reinvent the wheel and should go with a linear algebra library for this kind of problem.
PS: Keep in mind that your stiffness matrix might be singular if you haven't imposed any constraints.

How to solve a Stiffness matrix?


Did genocide occur in the Football War?

Question: In the Football War between El Salvador and Honduras, the El Salvador claimed that genocide had occurred in Honduras. However, was anybody actually prosecuted for these actions, or were these claims unfounded?
Comment: Going by the wikipedia page, it doesn't look like a credible claim. Note that it was made *before* the start of the hostilities. It seems that the Honduran government was engaged in a sort of nasty and brutal land grab versus ethnic Salvadorans who lived there but genocide is way too tall a word for that. But that's just based on wikipedia - maybe there is a dimension I missed here.
Comment: Could someone please explain how Salvadorans are ethnicly different from Hondurans?  Isn't it rather like the ethnic difference between... oh, North and South Dakotans?
Comment: which of the few dozen genocide definitions do you mean?
Comment: It is not uncommon for warring countries to accuse each other of genocide and atrocities. A more recent example would be Russian-Georgian war in Ossetia in which Russians led a huge (false and unfounded) campaign that Georgians were committing Genocide which was later disproved. (But Georgians in Ossetia did get Ethnically wiped out)
Comment: I suspect that the Salvadorean government is more likely to have committed genocide against Salvadoreans than the government of Honduras, and that the government of Honduras is more likely to have committed genocide against Hondurans than against Salvadoreans.
Answer: This wikipedia page (https://en.wikipedia.org/wiki/Football_War#Buildup) states:
"stating that 'the government of Honduras has not taken any effective measures to punish these crimes which constitute genocide, nor has it given assurances of indemnification or reparations for the damages caused to Salvadorans'"
- Wikipedia, Football War, Buildup, and Anderson, Thomas P. The War of the Dispossessed: Honduras and El Salvador 1969. p.105 Lincoln: University of Nebraska Press, 1981.
It's possible they might have, but they haven't released any such figures.

Did genocide occur in the Football War?


What is the difference between implicit and explicit analysis in ABAQUS?

Question: How can I choose between Implicit or Explicit Analysis in ABAQUS for a simple rectangular composite structure with 2 layers of unidirectional lamina? I am trying to do a linear-static analysis to capture the tensile strain for the specimen.
Comment: The choice between Implicit and Explicit analysis usually refers to dynamics modelling, not to statics. It's not clear why you are asking about Implicit or Explicit if you want to do a static analysis. The "Abaqus Explicit" software package is irrelevant for statics, unless you want to start a dynamics analysis from a steady "pre-stressed" loading condition.  Do you want a longer explanation of the difference between Implicit and Explicit *dynamics*?
Comment: Although, I am doing a linear static analysis, I wanted to understand when to use an Implicit or Explicit analysis. The option that ABAQUS offers when opened - is to create a model database with "Standard/Explicit model" which is the option I am using currently. Is this the right approach for the current problem? Also, a longer explanation would be appreciated, as it can help me draw a distinction. Thank you.
Comment: The one-word answer to that is "Standard" (which implies "Implicit"). I'll write a longer answer on the difference between implicit and explicit methods for dynamics.
Answer: The basic difference between implicit and explicit dynamics solutions is that an explicit solution takes account of the finite propagation speed (at the speed of sound) of dynamic effects through the material. To do that, you need a mesh which is fine enough to represent the spatial effects (e.g. a "stress wave" propagating through the structure), and time-steps of the same order of magnitude as the transit time of sound waves from each element to its neighbours. If the time steps exceed that size, the response will usually be unstable and the analysis will fail after a few time steps. The time step size is limited by the smallest element in the model, not by the average size.
Implicit solution methods smear out those local effects. The propagation of dynamic effects around the structure is controlled by the inertia (mass) of the structure, not by local speed of sound. You can think of an implicit solution method as assuming the speed of sound is infinite, or (equivalently) that any applied load affects all of the structure instantaneously.
The mesh for an implicit solution only needs to be fine enough to capture the overall deformation of the structure, and the time steps only need to be small enough to capture the frequency spectrum of the response that you are interested in.
Unless you need the fine detail from an explicit analysis, an implicit solution will usually run much quicker - possibly several orders of magnitude quicker.
For example if you were modelling the dynamics of a road vehicle for typical driving conditions, you are probably mainly interested in the low-frequency response to bumps in the road etc, and the propagation of stresss and strains from one end of the vehicle to the other as "stress waves" with a timescale of the order of 1ms is irrelevant. But if you want to model the deformation of the same vehicle in a crash, capturing the local high-speed behaviour of the structure as it deforms is important, and you need to do an explicit analysis. Typically, the time step size for explicit dynamics is of the order of a microsecond.
A static analysis is "implicit" by definition - the static response ignores any transient behaviour that occurs while the loads are being applied to the structure.
In Abaqus there is some commonality between the Explicit and Implicit (a.k.a. Standard) analysis procedures. For example, you might want to do a dynamics analysis where the loads are suddenly removed from a pre-loaded structure. In that case, you could first do an (implicit) stress analysis, and use the steady-state results as the initial conditions for an (explicit) dynamics analysis.
Note, none of the above mentioned linear or non-linear behaviour - both explicit and implicit methods can be either linear or nonlinear. But in "real world" applications, there are usually quicker ways to model the high speed linear dynamics response of a structure, so the models analysed with Abaqus Explicit are usually nonlinear.
Comment: thanks for your answer, can you please suggest me a book where I can get to know the basics of these methods and how I can use them to decide on a solution. I have used ABAQUS and am now using FEAP, please let me know how to get my concepts on numerical methods and finite element method strong...
Answer: In Abaqus, there are two primary analysis methods used for solving structural problems, namely Abaqus/Standard and Abaqus/Explicit (includes dynamic Explicit). Abaqus/Standard has static implicit and dynamic implicit and is suitable for solving smooth nonlinear problems.
However, the solution of these problems may converge with difficulty, because of the contact or material complexities which can cause a large number of iterations. Such analyses are more expensive in Abaqus/Standard due to the iteration which needs many sets of linear equations to be solved. Meanwhile, Abaqus/Explicit conducts the solution without iterating by explicitly advancing the kinematic state from the previous increment.
In fact, Explicit stands for explicit time integration. Although a given analysis may require a large number of time increments by using the explicit method, the analysis requires much less disk space and memory compared with Abaqus/Standard which requires many iterations. Hence, for problems in which the computational costs of the two programs are comparable, the disk space and memory savings of Abaqus/Explicit make it more attractive.
Answer: Further to existing answers: in a dynamic problem, an explicit method computes time-derivatives for use in updating through a timestep, by inserting into the dynamical equations the values of the fields and their spatial derivatives at the start of the time-step; an implicit method computes time-derivatives for use in updating through a timestep, by inserting into the dynamical equations the values of the fields and their spatial derivatives at the end of the time-step.  You may spot that there's a challenge in implementing an implicit method, in that, in advance of updating through the timestep, one doesn't know the values of the fields and their spatial derivatives at the end of the time-step: for linear differential equations, this can be sorted out exactly through a matrix inversion; for nonlinear differential equations, one has to estimate the values of the fields and their spatial derivatives at the end of the time-step iteratively.


How to call c++ functionality from java

Question: I have a Java program that is mostly GUI and it shows data that is written to an xml file from a c++ command line tool. Now I want to add a button to the java program to refresh the data. This means that my program has to call the c++ functionality.
Is the best way to just call the program from java through a system call?
The c++ program will be compiled for mac os and windows and should always be in the same directory as the java program.
I would like to generate an executable can the c program be stored inside the jar and called from my program?
Answer: If you have access to the code and want an 'interactive' experience with the external program (e.g., make call, get results, make additional calls), investigate JNI, which allows you to call C or C++ code from a Java application by including & linking JNI juice to your C or C++ app with .
See:
http://en.wikipedia.org/wiki/Java_Native_Interface
http://www.acm.org/crossroads/xrds4-2/jni.html
If you really just need a "launch app and get results" sort of solution, check out Runtime.exec(), which lets you launch an external program & capture its output.
See:
http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html?page=1
http://www.rgagnon.com/javadetails/java-0014.html
Answer: Assuming no better communication method is available (SOAP, ICE, Sockets, etc), I'd call the executable using Runtime.exec(). JNI can be used to interface directly, but I wouldn't recommended it. No you can't put an executable in the jar. Well you can, but you can't run it, since the shell doesn't know how to run it.
Comment: @Pavel: Less portable, less stable, tighter coupling
Comment: What's wrong with JNI? It's there for a reason, and it's definitely much better performance-wise than starting a separate process.
Comment: The problem with JNI is that if you make a mistake your JVM is liable to crash.  As in "segfault: code dumped".
Answer: You may also want to look at the Java Native Access API (JNA).
Answer: To answer your final question, you can't run an executable from within your jar.
However, you can store it within your jar and extract it to a temporary directory/file prior to running it (check for its presence the first time and extract if necessary). This will simplify your distribution somewhat, in that you only have the jar to distribute, and ensures that you're running an executable that matches your jarred Java code.
Comment: I did something similar to this once.  Worked well, but I am not sure if it would be difficult if you program needed to work on different platforms.

How to call c++ functionality from java


Should I use whey protein?

Question: I'm an average guy. completed a 30 days challenge recently.  The results are quite 'better'. I want to gain weight and mass muscle. I bought platinum Iso whey. My cousin highly discouragedd me to not use a whey protein. I told him I'll join gym after Ramadan In Sha Allah. But he forbade me. What should I do? I'm 7-8 kg under-weight.
Comment: What are his arguments against it and why do you think it would help you? Perhaps someone could sort out some misunderstandings
Comment: Just increase your food intake normally. Eat bigger portions, and eat more often. There should be no need to take protein supplements unless as a last resort.
Comment: How can your cousin forbid you to do something?
Answer: With building muscle (especially if you are underweight), you want to be in a slight caloric surplus and consume between 1.5 and 2x your kg bodyweight in grams of protein. More is fine, not necessarily beneficial, but not bad unless you go crazy with it (like getting close to or over 300 grams).
So let's say you decide to do 150 grams of protein a day, you would then want to plan and break that up over multiple meals/snacks throughout the day. Why? Because you want to consume a reasonable amount of protein at a time, your body won't absorb 150 grams in one sitting the same way it would absorb 150 grams across 5 sittings. So try to do 3-6 meals a day getting 20-40 grams per meal as your protein goal dictates.
Should you use whey protein? That's up to you. It's not necessary, but it is a great option as a post-workout protein source because it is absorbed quickly. Your main goal should be to get enough protein in throughout the day, and going a step further, reaching that goal by consuming reasonable amounts per meal through the day. Ultimately, whey is just one of many sources of protein.
Comment: Lactose is the sugar component of milk. Whey protein isolate (WPI) contains almost no lactose and is unlikely to be a problem for any except for the most highly sensitive of lactose intolerant people.
Comment: It should be noted that whey is created from milk. People who are lactose intolerant, have a milk allergy, or have a religious/moral obligation should refrain from taking whey specifically. There are other options.

Should I use whey protein?


Moving cards between boards

Question: Is there a way to move single cards between boards? I have lists that grow into becoming a project of their own and would be more managable in a separate board.
Answer: I've just tried having two boards open at the same time, in two different Firefox windows, and attempting to drag a card from one board to another. You can even drag the card out of the first window, so I believe that the answer to your question is "No".
However, the idea is being considered, and you could vote for it in the Trello on Trello board. I see it's in the "Next Up" list, which sounds promising!

Edit
Trello tweeted yesterday (2011-11-17) that this now implemented:

NEW! Move cards between boards. Just click the 'Move' button, select a different board, and sit back in amazement.
Answer: Possibly copy the board rename it and delete the stuff you dont want. Not an elegant solution i know.
Answer: You could create a new list and move items there (drag-and-drop). Then move the list to your target board (from the list drop down menu).

Moving cards between boards


Calibration of Z axis in Simplify 3D

Question: I'm using Simplify3d and a DIY 3D printer. The printer works fine and I've printed very nice objects with very smooth and beautiful surfaces BUT they are twice as tall as they should be! It is like they're scaled double in Z axis! I've checked everything, I changed steps/mm from 4000 to 2000 but it ruined the smooth surface. changing layer height just makes smoother surface and doesn't solve the problem. What am I missing in the settings?
Comment: Please add photos of the prints.
Answer: The steps per mm in firmware is the link to the hardware configuration/setup. Reducing by half must reduce Z advance by half. If your prints are twice as tall, you must have serious under-extrusion problems as when the printer is laying down molten filament for e.g. a 0.2 mm layer, in effect this is a 0.4 mm layer. If this is not the case, you should also calibrate the extruder.
Please re-calibrate your machine Z axis in firmware (most firmwares allow command M92 to set the steps per mm), not in Simplify3d, and then the extruder.
Comment: That's right. The point is that Z axis and the extruder calibration are very related to one another. My printer works fine right now. Thank you.

Calibration of Z axis in Simplify 3D


Will Superman have his powers while holding kryptonite and being near the sun?

Question: Assuming Superman is near the Sun, which gives him his immense power, what would happen if he was holding a small rock of Kryptonite in his hand?
Would the effects of Kryptonite cancel out due to power he gets from the sun's radiation?
Comment: I would assume that being powerless near the sun would result in his immediate death
Comment: The TL;DR of the accepted answer states: `A sufficient amount of green Kryptonite kills Kryptonians, completely dead in under an hour. Something the size of a walnut appears to be enough. The mechanics are never explained beyond disrupting the solar energy cycle which gives Kryptonians their power and then exposing them to a toxic dose of high energy radiation. Superman Vol. 2 Number 22 shows the death of the Phantom Zone villains.` Essentially it disrupts him being able to absorb solar energy so I'd say it wouldn't cancel out but I don't know.
Comment: @NiketPathak - Yeah, but there wasn't any Kryptonite around to weaken him
Comment: Welcome to SFF! [This question](https://scifi.stackexchange.com/q/42624/58193) appears to answer your question by describing how Kryptonite affects Superman. Not sure if it is a duplicate or not though.
Comment: Thank you. I am aware that he becomes weak when exposed to Kryptonite, but I what I wish to know is that what happens if he is near the sun at the same time and draws his power from there ? Would the effect of kryptonite be negated ?
Comment: @Valorum But we have seen in BVS that being near the sun got him back to life from almost near death.
Answer: The current explanation of the effects of Kryptonite is it drives out the energy stored in a Kryptonian's cells, weakening them greatly. It replaces the energy with Kryptonite radiation. If this happens long enough, the victim can die.
The Wiki listing notes:

Kryptonian characters have been shown to become immune to the effects
  of green kryptonite due to either long-term absorption of sunlight (1) or
  extremely high short-term exposure to the sun(2).

The effects mentioned occurred in Kingdom Come(1) and All-Star Superman(2), both of which which have a nebulous place in current continuity, so the effect may not be standard, or canon.
But based on those points, increased exposure to solar radiation may help slow the effect of the Kryptonite, based on the size of the Kryptonite dose.
The effects of Kryptonite are usually temporary, with possible mental issues causing mood changes and hallucinations lasting for some time afterwards (as explained in issues of Supergirl)
EDIT / Additional - Sci.com article on effect of Green-K

Superman utilizes energy from the sun at the cellular level.
  Kryptonite interferes with this process, but the method by which this
  happens is left ambiguous. The radiation from green kryptonite might
  interfere with and overpower the solar radiation providing Superman
  with his powers. Kryptonite could simply interrupt some organic
  process within his body the way that a plant's photosynthetic process
  could be blocked. Or, if Superman functions like a solar panel, then
  the radiation from kryptonite displaces electrons in Superman's cells,
  preventing the movement of the electrons to create energy flow
  (Wilson).
Comment: This would appear to be somewhat correct but unsourced. Could you add the relevant evidence into your answer?
Comment: Additional ref added. I may try and grab Mark Waid's ear on this for a better reference, though to be honest, he's about the best reference there is when it comes to stuff like this.
Answer: I put an answer out last month to "What actually Happens to Superman when he is exposed to Kryptonite?" question which may address this directly.  You can check it out here to get some perspective:
What actually happens to Superman when he is exposed to kryptonite?
The simple answer?
This depends on the amount of Kryptonite in proportion to sunlight exposure. I would theorize that, while in the sun and being hit from afar by a Kryptonite beam, or even holding a small [possible no more than 5 inch x 5 inch, flat or barely a few centimeters thick] piece of green K, while possibly being painful, the radiation is going to have no significant affect; Superman's cells would be reabsorbing the pure radiation faster than the Kryptonite could drive it out.
Evidence of this is given in the 2006 Superman Returns film; Superman literally had a roughly one-inch piece of kryptonite lodged in his back from a pure Kryptonite blade Lex Luthor had stabbed him with. This was after his powers were weakened by exposure to an impure Kryptonite LANDMASS the size of a large island or state. For visual reference, this is a shot of one side of said landmass against a helicopter.

Superman flew into the upper atmosphere [evidenced, due to the wind which was blowing while there], stayed in direct sunlight for no more than 30 seconds....

And was able to fly below the land mass, drill through it with his heat vision and physical punches to sever the tendrils from the earth, then lift and fly it out into space, ....all while showing only a certain amount of strain.

Keep in mind, again  that this is a land mass comprised of the one element that can weaken and kill him .... and Superman pushes it---- and the millions of gallons of water coming off of it---- into space. So he not only had enough power to shoulder the land mass....but enough to push it out of the earth's gravitational pull and toss it miles into the void. He then fell back to earth, survived re-entry, made a crater, and was unconscious for a day or so.
Oh, it should also be noted that while he was doing this feat, not only was he being exposed to still-growing Kryptonite from the island itself , seen here....

But he also had the aforementioned inch of pure Kryptonite* snapped off from the dagger still inside his back. Ere go, that Kryptonite was **still poisoning him while he was exerting himself to that level....and this was how strong he was after a.... lets be generous and say 30 second solar recharge.
This shows something pivotal: The extent to which Kryptonite can effectively counteract the solar energy in his cells is somewhat proportional to both the AMOUNT of Kryptonite, its PROXIMITY to him, and HIS proximity to the sun.
If Superman was capable of utilizing his powers to that extent while being exposed to green K externally and internally, then it should be safe to say that if he was closer to the sun directly and absorbing its radiation constantly, then the effects of the Kryptonite would be at least mitigated, if not not almost wholly dampened. This isn't to say he wouldn't experience some effects, such as pain and limited vulnerability, but if it works by "pushing the solar radiation out of his cells" and his body is being constantly inundated with fresh solar radiation, it wouldn't be in enough amount to completely poison him.  Also, we have to add to this that the closer Superman is to the sun, the more solar radiation he absorbs, and being within the sun for less than half an hour allows him to draw enough strength to effortlessly move planets; in this way, if we are to assume all his abilities are heightened, so too would be his healing factor.
Now mind you, this film wouldn't be applicable as "canon" to all aspects of Superman's solar metabolism, but it does give us some parameters for answering your question in a feasible way.


How to write testcase for my app?

Question: I am writing test case for my application. My application is a windows based application.My application is a news report app. Reporting the current update like sports live update... So when I download and run the application, while it create the database and when I insert, update, delete , edit the application, the database should be change the values. What are the sql queries to test my database ?  How to write an effective test cases  for this ?
Comment: too board, what have you written?
Answer: The good way to write effective test cases & make the testing process more saving time and effort. Here are some points to follow while creating test cases:

Keep your test cases simple and easy to understand
Include end-user perspective
Provide test case description
Include assumptions and preconditions
Give the steps involved
Give details of the test data
Make it reusable and modular
Assign testing priority
Provide the expected result and post conditions
Comment: "Give details of the test data" why? I want other testers to use their own data, so we actually test with more sets of data, not with the same values over and over again.
"Assign testing priority" a test case is just a test case, priority has the requirement we're implementing. Unless you have more test cases for one requirement.
Answer: You can follow below points in addition of above points for effective test case writing:

Written test cases should have a label attached to it i.e. if test case is created for sanity or regression etc.
You should be able to easily sort the test cases that can also be achieved if you add labels for modules/features it covers.
Test cases should be descriptive enough so that any layman can execute it by reading steps.

How to write testcase for my app?


Does publishing erotica on Kindle Marketplace require an ISBN, or is an ASIN sufficient?

Question: I heard a few years back that in order to self-publish erotica there, you needed an ISBN. Is that still true? Or is an ASIN fine?
Comment: Welcome to Writers! Please consider splitting this into two separate questions, Stack Exchange sites are designed so that there's a single answer that can be voted on and accepted per question. (I've temporarily placed this on hold until you can do this.) You may also find our site [tour] helpful.
Comment: 1. You need no ISBN to publish on KDP. I have an erotic book there without one. 2. I think you need to consult Amazon on that.
Comment: Apparently someone wrote a book about that - https://www.amazon.com/Violation-Authors-Navigating-Publishings-Guidelines-ebook/dp/B00U9UD9TA
Comment: You could also try asking on https://ebooks.stackexchange.com
Comment: Wow thank you prosepraise, how have I never noticed the ebooks stackexchange!  Joined.
Answer: In answer to what book identifiers are required for Amazon Marketplace;

No, an ISBN (International Standard Book Number) is not required to publish an ebook with Kindle Direct Publishing (KDP)
Yes, an ISBN (International Standard Book Number) is required for an Amazon paperback or hardback but Amazon can assign these for free, notes below.
Yes, an ASIN (Amazon Standard Identification Number) will be assigned automatically when you upload to KDP.  This is simply an Amazon product code.  This will be shared across all formats, ebook/paperback/hardback.  This is assigned as a unique key by Amazon on product creation.

There are no special rules by genre, erotica follows the same rules as classic fiction.
Neither ASIN nor ISBN can be changed, once assigned this is fixed.
Paperback ISBNs
KDP can provide you with a free ISBN to publish your paperback. We'll also automatically register your ISBN information with BooksInPrint.com®. This a global database of print books maintained by Bowker (the U.S. ISBN agency) and consulted by publishers, libraries, and booksellers.
The "Publisher" field on your paperback's Amazon detail page will read "Independently published." This free ISBN can only be used on KDP for distribution to Amazon and its distribution partners. It cannot be used with another publisher or self-publishing service.
It's important to some authors to provide their own ISBN because it allows them to choose their book's imprint of record. An imprint is a trade name that a publishing company uses to publish a work. If you use your own ISBN to publish your paperback, you'll be prompted to enter the imprint name as well. The imprint you enter must match either the imprint or publisher name that appears in Bowker (the U.S. ISBN agency).
Relationships
Each ebook can have a single ASIN, ISBN-10 and/or ISBN-13. The ASIN is only used on Amazon. The ISBNs will be common across all publishing websites, bookstores and libraries.  The ASIN will be common across ebook, paperback and hardcover on Amazon only. A new ISBN is needed for each version of the book. See example ebook;
ISBN-10: 0440863295 for ebook, 0385405081 for hardcover
ISBN-13: 978-0440863298 for ebook, 978-0385405089 for hardcover
ASIN: B007D15YSC


How to get my first gold badge

Question: I want to work towards my first gold badge on Stack Overflow and was wondering which gold badge was the most achievable.
Comment: Visit for consecutive 100 days.
Comment: This really is meta if you end up getting a gold flag for this question!
Comment: The Marshall badge is achievable fairly quickly: http://meta.stackexchange.com/a/278753/300177
Comment: You have 49 gold badges now. My congratulation !!!!!!!!!!!!!!
Comment: The Electorate badge.
Comment: I think that the electorate gold badge is easiest to get of the gold badges.
Comment: Shouldn't this post have been migrated to (or stayed on, perhaps I should say) meta stackoverflow?
Comment: When earning a gold badge, do we get reputation ?
Answer: Well, look at the list and see which one seems easiest to you.
https://stackoverflow.com/badges?tab=general&filter=gold

Fanatic: All you've got to do is visit the site for 100 days (although it's still eluded me for 2 years+)
Marshal: Raise 500 helpful flags
Copy Editor: Edit 500 posts
Electorate: Vote on 600 questions, and vote on at least one question for every three answers you vote on

All of these are nothing more than being bothered to do something. Gold badges such as Great Question and Great Answer require others to upvote the post; the above mentioned don't need any of that.
The numbers next to the badges show how many times each has been awarded. I figure the more times a badge has been awarded, the easier it is to get.
For what it's worth, the first one I got was Marshal.
Comment: My first was Unsung Hero - that's pretty easy to get too, if you're already answering questions ;-)
Comment: @RivieraKid I beg to differ. Unsung hero is incredibly hard, I don't think I will ever have a chance of getting that.
Comment: "Electorate" is less obvious (if not harder) than it seems as you need to stay above the a 1:3 ratio between votes on questions and on answers.
Comment: @MrLister You have to get your answers accepted, but not upvoted. In some tags, that's easier than in others. In my main tags, good answers **very** rarely don't get upvoted.
Comment: @DanielFischer, I guess I'm just.. um... "lucky" then :-)
Comment: @RivieraKid In terms of gold badges, in terms of rep, not so much ;)
Comment: @DanielFischer I got that while I didn't know it does exist.
Answer: I think the Electorate badge is by far the easiest to earn.  All you have to do is to vote on 600 questions.  You have a max of 40 votes you can use in one day.  So you could earn the Electorate badge in  a mere 15 days.
On contrast the Fanatic badge takes 100 days to earn and takes some discipline to make sure that you visit the site every day.  For me that can be difficult.  I usually seem to miss a day on the weekend.
The Marshall and Copy Editor badge could be earned fairly quickly as well.  However, you have to do a lot of reviewing and you may go crazy in the process.
Comment: Fact is the badge is given for both upvotes and downvotes. Please do NOT put wrong data on purpose! Someone noticed your mistake and fixed it, no idea why you oppose the truth.
Answer: The most easy gold badge is Fanatic.  Just be active for 100 days in a row and you get it.
Comment: If you're in hospital and worried about your gold badge streak breaking... well, actually, I guess that does make you a Fanatic.
Comment: In a way, Copy Editor and Electorate are easier. Spend one day in Hospital or such, and for Fanatic, you're back to 0. On the other hand, if you don't have the bad luck of missing a day due to outer forces, Fanatic is really much easier to get.
Comment: A Real Programmer just creates a cron job to visit the site once a day for them.
Comment: For both Copy Editor and Electorate you need more than 1 reputation. So you need the action of others.
Comment: Fanatic badge is for fanatic computer users. Non fanatic ones sometimes go for a few days trekking or in any other way far from a connection. I see this one more as an attribute/characteristic than an achievement.
Answer: Going purely by statistics
(https://stackoverflow.com/help/badges),
as of March 22, 2014,
125,000 users have received the Famous Question Gold Badge. That out-ranks each of the next two most common Gold Badges, Fanatic and Great Answer, ten to one.
I'd say asking a popular, solid, new question is the best bet.
Update, 5 Years Later
To support this, now looking back at my network profile, I see that while I am neither a Science Fiction nor a Fantasy fanatic, I have made a total of 4 posts on the Science Fiction and Fantasy StackExchange site and I have 1 gold badge. What is the badge? Famous Question.
Likewise, in the Ask Different StackExchange site, I have made only 5 posts and have 1 gold badge. What is the badge? Famous Question.
Comment: Why the down votes? If you asked, "What class is easiest to get an A in?" and the statistics showed that 200,000 people got an A in Underwater Basket Weaving whereas only 20,000 got in A in any other class, then I would say Underwater Basket Weaving is the easiest class.
Comment: Although the most of these badges have been awarded, this badge can be awarded multiple times. It is also easy to ask solid and new questions, but the popularity of a question is a matter of luck, not skill. It also takes a lot of time for a question to get that many views.
Comment: The next time you think of a good question, give it to me please!
Comment: I suppose that's true. After I posted this meta answer, without trying, I've now received 2 famous question badges, which account for 2 out of 6 of my gold badges.
Answer: Earn a gold badge in 50 days or less
Badge: Marshall
Description: Raise 500 helpful flags
Method:
This is a "moderation" badge earned by helping clean up the site from questions, answers and comments that are:

spam
rude or offensive
not constructive
obsolete
too chatty
low quality
...
...
other (textbox)

Currently, I get about 50 flags per day on Stack Overflow. The number varies based on reputation and the number of helpful flags you've raised.

How many flags do I have?
When you start out, you are allotted 10 flags per day. This number may increase to up to 100 flags per day:

You get one bonus flag per 2000 reputation.
You are awarded additional bonus flags when you flag correctly - one bonus flag for every ten net
helpful flags (helpful flags minus declined flags).

source: https://stackoverflow.com/help/privileges/flag-posts

One helpful way to use this flag is to eliminate "noise" in the comments, such as "Thank you" and "You're welcome". These comments are generally "not constructive" and "too chatty".
So, run a search for "You're welcome" in comments only. You'll get TONS of results. Flag away.
Plus, since you're searching for "You're welcome", you'll get the "Thank you" in a previous comment.
You'll exhaust your daily flag limit in minutes.
Let's say your flag limit is 30/day. You'll have your Gold Badge in less than three weeks.
Just be careful not to delete comments that contain valuable information. Often you'll see a comment with useful feedback ending with "Thank you". Deleting those may be unhelpful and inappropriate.
Read this post before flagging:
https://stackoverflow.com/help/privileges/flag-posts
Here's a tool for searching comments in Stack Overflow:
https://data.stackexchange.com/stackoverflow/query/edit/477136
Comment: "Flag away", well, please keep in mind that there are humans verifying your flag. You don't want to allocate the entire time a mod has for just useless flags. Flag something that really matters, like the loads of spam on some sites. MSE here is good for 5-10 flags a day, just for spam.
Comment: There's no point in earning a gold badge at the expense of the site / moderators. I believe my suggestion is helpful and a win / win. Also, for somebody like me, who likes to read a post from top to bottom (including comments), having useless chatter removed is appreciated.
Comment: @rene, the flagging tool specifically targets comments that are *too chatty* or *not constructive*. By removing these unnecessary messages, including "Thank you" and "You're welcome", I think we're  cleaning up the site and making posts more efficient, without violating *even the spirit* of any guidelines.
Comment: @PatrickHofman, agreed. I thought I made that clear in my answer. I'm advocating this method as a way to contribute to the site while earning a gold badge.
Comment: Moderators are going to hate you and I know cases where users were flag-banned because they used naive queries like yours to flag comments and/or posts. Related: http://meta.stackoverflow.com/questions/280546/can-a-machine-be-taught-to-flag-comments-automatically
Answer: I agree with @Linger, the Electorate is the easiest to earn; it was my first gold badge.
Let's compare it with Fanatic:
Fanatic
You need to visit 100 consecutive days. If you forget to visit the site on the 99th day, the counter resets to 0! Believe me, it's very frustrating :)
Electorate
You need to vote on 600 questions (up or down). Since you have a limit of 40 upvotes a day, you will need at least 15 days to get it! It's a lot less than Fanatic and don't need to be consecutive.
With this query you can track your progress. Just put your UserId in the filter.
You can find your UserId in your profile URL, for example, mine is 890890:
https://stackoverflow.com/users/890890/fabriciorissetto
Comment: For electorate, it tells me that I have 21 days remaining. Isn't 15 minimum?
Answer: Reviewing posts you can easily get some of the badges including gold, and some are awarded
multiple times
You can review posts here based on your reputation - https://stackoverflow.com/review
Comment: Well, since reviewing is limited to 40 per day, it means you need to spend at least 25 days reviewing tons of things. It's really not easy, and also requires some initial reputation to begin with.
Comment: Yes its not easy and takes some time, but good for the people who enjoy doing reviews and post edits :). This way you can get multiple badges.
Comment: Aren't those supposed to be all checked and golden? ;-)
Comment: This is the easiest way to earn unlimited number of gold badges now on SO.
Answer: Build a program that logs in with your account and visits your profile page once. Make a scheduled task or cron job that runs it once every day, forget this and come back 100 days later, you'll get a Fanatic badge on every site you have an account on, provided you coded your program correctly :)
Comment: Doesn't this require that your pc stays on for that many days? I'm more the type that closes a computer at the end of the day.
Comment: @pensum A cloud server is undoubtably a better option than your PC and it can cost as little as US $3 to $5 a month.
Answer: I think following gold badges are easy to be earned,

Electorate
Fanatic
Steward (can be won multiple times by type of review you do)
Copy editor
Marshal

I feel Steward is easier than Marshal as I can review 20 posts under categories of triage, first post & late answer. So getting 1000 reviews for each categories will take 50 days to earn 3 gold badges. These categories are opened as per reputation you earn, I'm above 1000 reputations so I have access for 3 categories here.
Note: Care must be taken for reviewing mentioned in comment provided by S.L. Barth
Comment: Triage only exists on Stack Overflow. Also, even if one only reviews to obtain the badge.. PLEASE review carefully! The purpose of /review is quality control. To do reviews means shouldering some of the responsibility for keeping up the site's quality.
Comment: Steward might be "easy" on Stack Overflow where the pending reviews stack in thousands, but that's not the case for about 90% of other sites.
Comment: @S.L.Barth I can imagine the case if I were new user and posting first post and got bad reviewers. It is of course responsibility. Perhaps they have added test cases to check whether you are paying attention or just faking it.
Comment: Please don't use `code formatting` for highlighting. Instead use **Bold text** or use links.
Comment: Correct, that is exactly why review audits were added.

How to get my first gold badge


Constrain the movement of rigid bodies to two axes

Question: Is there a way to have an object, a ball for example, fall down and bounce up, using rigid body dynamics, but with its movement locked to two axes? So basically that would make for a 2 dimensional simulation.
I tried using a generic rigid body constraint but that doesn't seem to do anything when I lock a single axis. Now I'm faking it by putting the ball between four planes, in a box basically. Although there should be a better way to achieve this.
Answer: Use a copy location constraint on the ball to some other objects x, y coordinate.

Ball locked to bounce on plane origin (0, 0, 0)


Inverter PWM frequency

Question: I am making a modified sine wave inverter. The PWM wave is generated, switched using transistors, and then passed through a transformer. What is the PWM frequency required to generate a modified sine wave of 50Hz?
Answer: Here are a few pictures: -

They are all using (from what I can see) different PWM frequencies to get the same result. Clearly the higher the PWM frequency, the less grainier will be the final sine wave but, on the other hand there could be more losses of you decide to use (say) a 1MHz pwm frequency as opposed to 1 kHz.
The best frequency to use is totally dependent on your input specification and the availability of hardware in your area plus your cost/build requirements. I don't have that information - do you?
Answer: You have to use a PWM with a base frequency that is several times higher than the sine wave frequency you like to generate if you want the sine wave to be generated without too much distortion. E.g. solar inverters generally work with PWM frequencies from 10 kHz to several 10th of kHz. The amount of distortion largly depends of the power you want to put through the inverter in comparison to the filtering done with output capacitors, coils and perhaps an output transformer.
A quite detailled insight into this matter with practical aspects gives this Major Qualifying Project about PWM Techniques: A Pure Sine Wave Inverter.

Inverter PWM frequency


Why do professors give 'updates' about their unpublished, ongoing research?

Question: Why do some professors arrange meetings to give updates about their ongoing work?  The updates are certainly exciting, especially for the other people who have been in the lab for awhile and was involved in the work in some small way.  But these meetings are also open to visitors, and visiting professors and post docs come too.  Isn't there a fear of outsiders (or even insiders) scooping the ideas and beating them to publication?  Although I highly doubt that, but I'm curious to know.
Comment: The very fact that those meetings are public means that it also ensures that there is a record that that professor had that idea at that time, making it harder to scoop that idea without being accused of plagiarism. In practise the arguments by Fabio and brightskies will most of the times play a bigger role.
Comment: IMHO, the potential of attracting new collaborations usually outweighs the remote possibility of a scoop.
Comment: I think far larger than the fear that their work will be scooped, is the fear that their work will be unnoticed.
Comment: @BobJarvis What? That isn't even closely equivalent to what this sort of 'update' is about.
Comment: In an ideal world, it doesn't matter who finished the research. If the research is publicly funded, it is owned by the public, any part of it that is done. Also, the goal is to solve a problem/learn an unknown/etc. not to take credit. However, sadly for a temporary postdoc looking to get a more secure job, and with the current publish or perish state of the academia, anyone other than a tenured faculty doing this is taking a big risk. For a tenured professor, of course, this isn't a factor, so they share freely and enjoy it.
Answer: The main reason is to attract interest to their current and future work, in terms of both public interest and potential students, scholars, and postdocs who might want to work with their labs. Talks are a good way of accomplishing this. Research isn't meant to be conceived, designed, done, and published in a cloistered off world. Anyone who believes this shouldn't be in research.
If the point of research is to advance/exchange knowledge and to improve life, then it deserves to be made a public, accessible resource. Perhaps even work that hasn't been completed. It's important for researchers to be transparent about their work, rather than trying to hide it, especially when they accumulate so much funding, some of which often comes from public, taxpayer sources (i.e. government funds).
You might think visitors are outsiders, but it's important to keep sight of the fact that they likely helped fund the research in some way, and more importantly, that they're part of the people your research should be trying to help -- and there shouldn't be such distinctions on this account between outsiders and insiders.
Answer: Science is a human activity. There is no point in doing research if nobody reads it. Your research becomes relevant once you can engage with people. Bill Thurston has an essay on this, focused on math, but I believe it can be extrapolated to many other areas: https://arxiv.org/pdf/math/9404236.pdf
Comment: We almost need a Godwin's law-style disclaimer for Perelman...I feel like his name comes up as an exception in *every* conversation about the collaborative nature of math/science/academics. Also, for the actual statement in this answer: "There is no point in doing research if nobody reads it" Perelman is no exception: you know his name because people read his work. And he did *his* work based on reading the work of others.
Comment: That's a bit off - Perelman didn't engage with anyone except for his mom and a few of his fellow Russian mathematician friends, yet his work couldn't be more relevant today.
Comment: That only applies to major breakthroughs. If you solve something that many *people* is already looking into it, you will have their immediate attention. But if you want to propose some new theory, for instance, you have to engage with people.
Comment: @user75201 - True that it ain't no general statement, but at the same time, generalizing from Perelman ain't very wise too. He's probably more of an exceptional case, instead of being a general example. However, I see your (and the OP's) point too. :)
Comment: @user75201 Perelman had to explain his proof before people started buying it: http://www.math.columbia.edu/~woit/wordpress/?p=77. Similarly, the abc's conjecture might have been proven, but the relevant mathematical subcommunity is still working on understanding the proof.
Answer: Professors giving Update , under an okay from institute /university / funding society is to be viewed in a positive way. Too often scientists have been criticised for working in splendid isolation (sometimes meant ivory towers ) and with lesser accountability to public at large. Ongoing research projects of a larger dimension and duation do require an internal review periodically ;  this being made more open and transparent should not ideally invite objections. However , this is best left to professors themselves , as an option to share ;  making a rule or compulsion carries am apprehension of becoming counterproductive.     Prof ME Yeolekar  , Mumbai.


How do I compute combined tensile strength?

Question: If I know the tensile strength of a pin, how do I compute the total strength of multiple pins?  That is, 2 objects are connected by multiple pins, evenly distributed, each with a height of $2mm$ and a cross sectional area of $3.33mm^2$.  For some reason the answer of just multiplying the tensile strength of each pin by the number of pins, doesn't make 100% sense to me.
Answer: The short answer is yes, it is that simple.
Think about it this way. The pins are connected to end plates of a given area. If all we're worried about is the tensile strength, we can place a one dimensional force on each end plate to put the system in pure tension. Now, split the system into a couple parts and do a force balance.
If we split it right down the middle, so that we're seeing the actual force on the top plate, and the internal force along each of the pins. These two forces have to be equal, otherwise the system would be in motion, meaning the pins have yielded or fractured.
Now, to calculate the stress in the pins, we simply divide the force applied across all the pins by the total area. Because in this case, the pins are all of even cross sectional area, the stress will be divided evenly between them. The implication of this is that none of the pins should fail before the others, and any difference in their tensile strength is due to manufacturing defects or variations, so we can just multiple the tensile strength of a single pin by the number of pins to get the overall tensile strength.
There is an important assumption here that the pins are distributed evenly on the plates. If the pins are lopsided, they're going to end up under some amount of bending, which complicates the stress calculations in them and adds to the stress that they see under the same applied load.
If we make the pins of variable cross-sectional area, then the load begins to concentrate in the larger pins, but it should still end up with the same stress in each pin because the load will distribute proportionally to the area, which is how we calculate stress anyway.
Where this gets more complex is if the pins are made of different materials or treated differently to change the tensile strength. This is essentially creating a composite material, and there we have to take into account volume fractions to calculate new yield and tensile strength numbers, but also consider which material fails first. For further reading I'd suggest chapter 3 in this MIT book (that is a 128 page pdf, beware if you're on mobile).
Comment: This assumes the top plate is infinitely stiff, correct? If it has similar flexibility as the pins, you wouldn't be guaranteed equal stress on different sized pins, right? (Not disagreeing with the assumption, just trying to clarify.)
Comment: Yeah, the infinitely stiff (or even just much much stiffer than the pins) assumption might not be totally necessary, but it's a good, simple way to ignore any effects of the plate, and use it simply as a platform to transfer the load to the pins evenly.
Comment: @Ethan48 Essentially, yes. If the plates are not significantly stiffer than the pins, you'll have to take into account their behavior in calculating how the force propagates through the system. I think that's a safe assumption though, if the total area of the pins is only a small fraction of the area of the plates.
Comment: @Ethan48, & at Trevor, no this does not assume an infinitely stiff plate. It assumes a perfectly equal distribution of forces to all pins. Even an infinitely stiff plate, with unsymmetrical load placement (relative to the pins), will not distribute the load to all pins equally. When in doubt, make a free body diagram.
Comment: @WilliamS.Godfrey Sure, it assumes an infinitely stiff plate that is also constrained to a single degree of freedom. I think Trevor and I both figured that was a safe assumption based on the question.


Work done in irreversible isothermal expansion against vacuum

Question: Why is the work done in an irreversible isothermal expansion against vacuum equal to zero?
Answer: A system does its maximum amount of expansion work when the external pressure is equal to the pressure of the system all the way through the expansion process.
At constant pressure work done is given by:
$$w=-p_\mathrm{ex}\Delta V$$
Where $p_\mathrm{ex}$ is the external pressure. Therefore the minimum work done is when the external pressure is $0$, which is the case under vacuum. This would mean that the work done under vacuum is $0$.
This is called free expansion. The greater the opposing force then the greater the amount of work done is (as work is equal to force applied over a distance). Therefore when the external pressure is $0$ there is nothing for the piston to push against, because there is no opposing force, no work is done by the system.

If you are interested to see where $w=-p_\mathrm{ex} \Delta V$ comes from then note that
$$w=Fd$$
Because pressure can be given by $P=F/A$ and volume can be given by $V=Ad$ we can see that $$w=\frac{F}{A} Ad = p\Delta V$$
This is work done on the gas. For work done by the gas, we put a negative sign in front of the pressure term.
*Note that this is at constant pressure.
Comment: Good answer. It really is intuitive as well, work is defined by a transfer of energy from one system to another - if the other system has vacuum, then no change in its volume will transfer any energy to it. Trying to pump something with vacuum on the low pressure side of the pump will not produce any gainful results.
Comment: @PiyushKumar  you wouldn't mind marking my answer as correct then would you? ;)
Comment: Yeah sure george!!


In history of algebra, who was the first to add one equation to another equation?

Question: In history of algebra, who was the first to add one equation to another equation? Someone gave me the name of an Italian mathematician of Renaissance period, but I lost the email. I wish to make it a bit more precise: adding two equations (hence involving unknowns), not just equalities: the latter was apparently dealt with by Euclid.
Comment: Do you mean taking linear combinations of simultaneous equations?
Comment: Yes, in modern terms it is a linear combination of simultaneous equation. In old times it was likely to be adding one of two simultaneous equation to, or subtracting from, another one with the simpler to get a simpler equtions.
Comment: Is the question about *any* use of $f = 0 = g \Rightarrow af+bg = 0$ for polynomials $f,g,$ or only the special case where it is used to eliminate a variable?
Answer: For sure, the technique was used by Leonhard Euler (15 April 1707 – 18 September 1783).
See : Elements of Algebra (English transl., 1822), page 208:

Since the two equations are,

$x+y=a$, and
$x-y=b$;

if we add the one to the other, we have $2x=a+b$.

The first German edition of the Elements was in 1770.

An earlier example seems to be in Gerolamo Cardano (24 September 1501 – 21 September 1576)'s Ars Magna (1545), but we have to consider that we are reading a modern English translation: the original Latin text can be quite different (see Caput IX (page 21)).
Comment: The second link is returning 404.


Can't log into PokeGo. Not accepting any of my possible email accounts!

Question: So I was having trouble logging in, like most everyone seems to be and decided to try logging out - now I can't get back in. I believe I'm having a different problem than others: when I log in using the Trainer way, it threatens to lock me out of my account if I go over the amount of tries. I swear I didn't use Google to sign up. Logging in with Google says my password is incorrect. And when I try to recover my info using the Trainer recovery, it tells me none of my email accounts are tied to my PokeGo! Is there any way to get my information? Please, I don't want to start all over.
Answer: If you were playing on a PTC account, you have to login with the PTC option using your username, not your email address.
If you were playing on a Google account, you have to login with Google using the appropriate email address and password.
Comment: That is what I've tried. It does say "username" and that's what I have done. But when I asked PTC to send me a new password in case I miss typed, it told me that there is no account tied to my emails. Shouldn't I have a confirmation email that was sent after my signup? I've checked my inboxes and yes, also my junk email folder to no avail.
Comment: Have you ever registered a PTC account?
Comment: I thought I had when I signed up on the PokeGo app.
Comment: If you haven't registered, you used your Google account to play.
Comment: Doesn't matter. My account doesn't exist somehow. Even having reset my password, entering the correct info signs me up for a new account. Thank you for your input anyway.


Can I cite a paper published after the initial submission of my paper?

Question: I wonder if it is allowed to cite a recent paper, published after the initial submission of my paper. In the revision phase I am adding some missing references and I would also like to refer to some very recent papers. Could this be a problem?
Answer: There is nothing special about the initial date of submission.  As such, it is entirely acceptable to add new citations, including for recently published papers, at any stage except for some journals' final proofing (where they really just want to confirm their formatting and copy-editing).
Moreover, in many cases it is not just acceptable but required, especially given that review may be a very lengthy process.  For example, I am in the middle of a revision right now of a paper that had an unusually long initial review for my field---from first submission to submission of the revision will be nearly 18 months.  In the revision, we will most certainly be citing new work, including some of our own other recently published work, as a necessary part of addressing the comments of the reviewers.
So, in short: yes, cite whatever is useful to cite, regardless of its publication date.
Comment: You even see it added after the final acceptance stage sometimes, but it's usually a special "note added in proof". See [Note Added in Proof](http://www.apsstylemanual.org/oldmanual/parts/note.htm) from the American Physical Society style manual, although it's seen in other disciplines as well. For additions like this before acceptance, no such special note is necessary.
Answer: "Disputable"? No, it's probably fine. Check with the editor of your article to be sure about the journal's policy for these kinds of changes after acceptance, but I can't imagine it would be a problem unless whatever the referenced paper concludes necessitates substantial changes to your own work. That being said, if the journal you have submitted to prints submission, revision, and acceptance dates, you're not going to get hammered for failing to cite it, unless, again, its conclusions are substantially at odds with your own or would indicate a need for a major revision.
Comment: Maybe I used inadequate word (disputable). I wanted to ask whether this is an acceptable practice.


Halogenation of an alpha-halogen ketone in acidic conditions

Question: When a methyl ketone is submitted to halogenation in acidic conditions with two equivalents of a halogen, the first halogenation happens at the secondary alpha carbon atom , while the second halogenation happens at the primary alpha carbon atom. Why is it so? Why doesn't it happen on the same carbon atom (the secondary one)?
Comment: What is the specific molecule you're asking about?
Comment: Actually any ketone. Even acetone with two methyl groups, will have the halogen atoms ending up at the two different alpha carbon atoms.
Answer: The same mechanism discussed in my answer to your earlier question on acid catalyzed halogenation alpha to a carbonyl still applies here.  For reference, here is the same link supplied earlier that shows the mechanism for this acid catalyzed halogenation.
In that earlier answer I said that the enol that "produces the more stable double bond (the one that is more highly substituted)" is the enol that will form and react nucleophilically with the halogen to produce the alpha-halo carbonyl product.  In light of your new question, the statement that more highly substituted double bonds are more stable needs some qualification.
The closer in electronegativity a substituent is to carbon, the more it will stabilize a double bond.  Consequently, the more alkyl groups attached to a double bond, the more stable the double bond (barring large steric effects).  On the other hand, fluorine destabilizes a double bond.  It is so electronegative that it prefers to bond with orbitals high in p character.  When forced to bond to a double bond $\ce{sp^2}$ orbital (that is enriched in s character) destabilization results (see this earlier fluorobullvalene example for more on why fluorine "hates" to be on a double bond).
Based on its electronegativity, chlorine should be somewhere between fluorine and an alkyl group in terms of its ability to stabilize a double bond.  If we compare the heats of formation of 1-butene (-0.1 kJ/mol) and trans-2-butene (-11.2 kJ/mol) we see that placing the methyl group on the double bond stabilizes the molecule by 11.1 kJ/mol.  If we compare the heats of formation of allyl chloride (-5.6 kJ/mol) and trans-1-chloropropene (-12 kJ/mol) we see that the placing the chlorine group on the double bond stabilizes the molecule less, only 6.4 kJ/mol.
These differences mean that we will have much more of the enol without the chlorine on the enol double bond, then we would have of the enol without the methyl group on the enol double bond.  So we have more of the unsubstituted enol in the chlorine case and the enol with the chlorine on the double bond is much less nucleophilic (less reactive) due to the electron withdrawing inductive effect of the chlorine substituent.  These two factors combine to make the second alpha-chlorination take place on the unsubstituted side of the molecule.
As to steric effects, they probably don't play a significant role.  One metric commonly used to compare "steric size" is the cyclohexane A value.  The A value for chlorine is 0.43, much smaller than the A value for methyl (1.7), suggesting that a chlorine substituent is smaller than methyl substituent.
Comment: Why would then the second alpha halogenation in basic media happen at the same carbon atom?
Comment: @Marko Because the halogen substituents increase acidity.
Comment: But it increases the acidity in the first case, too.
Comment: @Marko  In the base catalyzed case it is about which proton is easiest to remove (which resulting carbanion is the most stable).  The more chlorines attached to a carbon, the weaker the remaining C-H bonds, the more stable the resulting carbanion.
Answer: Most probably due to steric reasons and the electron withdrawing effect that the halogen has on the substituted methylene group.


What is the attitude of Buddhists to "repulsive animals"?

Question: I recently started watching a documentary about Buddhism and animals and am curious to understand how the relationship extends to often what we as humans consider "repulsive" e.g. rodents, cockroaches, etc. If the intention is to keep these at bay without harm, how does one achieve that?
Comment: I've amended your title so it summarises the content of the question. Please rollback if it is not an appropriate edit.
Answer: The most skillful way would be to ordain as a monk, foregoing the ownership of a house and not having to worry about it. Aside from that, the most you can probably hope to do is keep a clean house and don't let the conditions arise for  them to come to you.

Here's a good video on this issue: Ask A Monk: Dealing With Pests
This video includes advice that there are three Buddhist ways to deal with a problem:

Avoid the situation (e.g. shave head to avoid lice)
Find alternative non-violent solutions (e.g. repel ants using talcum powder or butter instead of poison; catch rats using humane traps; catch mosquitos in a cup and carry them outside)
Accept the situation and let go (mental well-being is more important than physical well-being; and mindfulness often leads to being able to resolve a situation)
Comment: That assumes that a monastery is not plagued by similar conditions or environments.


3.5" Touch screen loss

Question: I have an RPi 2 B running a custom Raspbian kernel provided by the vendor. Touch screen is a 3.5" LCD. It works fine until I do either apt-get dist-upgrade or apt-get upgrade. I still get the display working, but I lose the touch screen ability. How do I prevent the loss or recover the ability to use the touch features
Answer: You will need to contact your vendor and follow their upgrade instructions instead of using apt-get. Likely there is a separate repository for this image. Worst case you need to find out which packages are critical to the touchscreen setup, and manually force those to be held back to the current version in apt.
Comment: Yep...I had the same issues. Too bad touchscreens are such a pain becuase of this!

3.5" Touch screen loss


Make Part Of Material Transparent

Question: I want to make the blue part transparent and the non-blue part not transparent, there are no vertices where the grey part is so I can't just make a new material.
Answer: What you can do is that you can edit a copy of the texture in an image making program like Paint.net.
First, make the area where the non-blue strands are black and the blue areas grey or white. If you want the blue area to be translucent (between opaque and transparent), choose grey. If you want it to be fully transparent, choose white. After you do that, save the image as a separate image file (I'll call it alpha.png).
Now go to Blender. Go to Cycles Render.
Then, go to the material's nodes in the Node Editor. Add an Image Texture node and load alpha.png in it. Connect its Color to a Transparent BSDF's Color. Then, add a Mix Shader node. In one Shader socket on the left side, put the Transparent BSDF. In the other, put the BSDF your actual texture (NOT alpha.png) is connected to. Finally, take the shader socket on the right side and connect to the Material Output.
Here's the explanation; connecting alpha.png to the Transparent BSDF creates something called an alpha. White means fully transparent, grey means between transparent and opaque (translucent) and black means opaque.
Answer: Use an image with an alpha channel
Comment: Please specify how that would be implemented, so that a new user could do it.

Make Part Of Material Transparent


Is 4K good enough to choose for special footage such as weddings?

Question: Resolution is obviously better in 4K but can anyone give some insight as to whether other factors of video quality are being compromised? If so, does it make sense to record in 1080?
Answer: Where are you planning on exhibiting the footage? In my experience, the average consumer has a low-quality TV they bought because of the price, and they have the factory settings that look awful because they don't even know that they would want to change them, let alone how that would happen. In my opinion you're wasting your time because your client probably won't be able to tell the difference.
On the creation side, you're multiplying the amount of data captured by 4. That increases the cost of filming (more memory cards to save it), storage (more hard drives to use while editing), and editing (need a better graphics card, more RAM, and likely more time).
If you have clients who will truly benefit from 4K, by all means, use it. But if you're doing typical videos for the web, corporate or home televisions, it's probably not worth it. If you're creating content for large outside displays that actually reach above HD, or for professional projection in a theater, then it could be worth it.
FWIW, most television shows are shot in HD, and even some feature films. I've never heard anyone complain about the quality because of the lower resolution. If I recall, parts of the first Captain America movie were shot on a Canon 7D, which only does HD. I know of nobody who said those parts were terrible or even noticed them. (Here's an article about it on Canon's web site.)
Comment: @Bendy For what it's worth, I got married in the 1990's. I could have hired someone to do it in HD, but I wouldn't have had anything to watch it on for another 10+ years! But it doesn't matter for 2 reason: 1) We've only watched our wedding video a handful of times in 17+ years. 2) When we watch it, we don't even notice the low resolution. It mainly reminds us of the day we made our commitment, and how far we've come since then. The memory is what's important, not the resolution of the video. If you want 4K, go for it. But you're not missing anything if you don't.
Comment: Thanks very much - I would actually be the client in this case. Capturing our wedding, only a few people offer 4K and the others are saying that although it would be lower resolution, the video quality is better. I'm thinking ahead 20+ years and wondering what would be the best technology around today to capture it on
Comment: 4K is not lower resolution, Bendy - I'm not sure why you think that.
Comment: Hi, I do quite a bit of Wedding videograhpy and I have not had anyone request 4k as a lot of people dont even know what it is, bare in mind as well if they are shooting 1080 HD or 4k putting it on a DVD to watch is still only going to be DVD quality, most people dont even have a device to view 4k some not even 1080 HD, I shoot everything in 1080 HD and it looks amazing, for future proofing, it is hard as 4k will jump to 6k, t0 8k to 10k +++++ base it on the skills of the person not the kit they use
Comment: Thanks @user1118321 for putting it into perspective ;-) I've found people that will do do the wedding in 4K...just that other videographers who 'only' offer HD are saying that 4K hasn't matured enough yet to capture the framerate/color depth/contrast you can get in HD