How can I permanently remove the boot option "quiet splash"?

Question: When booting, I'd like to see the kernel output without having to edit the GRUB line on each boot. How can I do that?
Answer: Open a terminal and type the following:
sudo  gedit /etc/default/grub

Then look for a line like this in the opened file:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

It may have other options there as well, but just remove quiet splash and:
sudo update-grub

Comment: the final step is to run `sudo update-grub` for any changes made to the grub.config file to be used, otherwise any changes made will not take effect until grub runs an update for another reason(like a new kernel install), otherwise your answer is good....also the question does not say which version of Ubuntu...if newer than 12.10(?maybe) gksudo will not be installed by default the correct way in that case is `sudo -i gedit.......`
Comment: Ah yes forgot the sudo update-grub! My bad! I didn't know that about gksudo, thanks for the info, and the -i sudo tip!
Comment: @TrailRider , the correct one (from now on) is `pkexec` and not `gksudo` (as you said correctly it has been removed due to some problems).
Comment: @NikTh I know that `pkexec` was *going* to replace `gksudo`, however I don't know if it did, last I knew it was not installed be default either, it may be now, but I know that `sudo -i` does work.....thank you for letting me know that `pkexec` is now available...
Comment: If you only have "quiet splash" in it, use this `sed -i 's/^GRUB_CMDLINE_LINUX_DEFAULT=".*/GRUB_CMDLINE_LINUX_DEFAULT=""/' /etc/default/grub
`
Answer: Open a terminal (Ctrl+Alt+T) and issue the following command
pkexec gedit /etc/default/grub

or
sudo -H gedit /etc/default/grub

I assume here that gedit is installed on your system, if you prefer another editor use the appropriate name (e.g. leafpad, kate...etc).
Search, find and edit the line
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

to
GRUB_CMDLINE_LINUX_DEFAULT=""

proofread, save the document and then run in terminal
sudo update-grub

Comment: Thank your too for your reply. When I tried to ran your first line, it didn't work: `~$ pkexec gedit /etc/default/grub
error: XDG_RUNTIME_DIR not set in the environment.

(gedit:6024): Gtk-WARNING **: cannot open display: `
Comment: Although your comments to the other reply explains it, I'm too unfamiliar with this particular program so I just used `sudo`.
Comment: I added `sudo` again as an alternative. At 14.04 (that I have) `pkexec` works as it should. It seems that you have to provide some variables in order for `pkexec` to work properly. Try
`pkexec env DISPLAY=$DISPLAY XAUTHORITY=$XAUTHORITY gedit`
Answer: It's in /etc/default/grub. Make your changes there and update grub with sudo update-grub


Set Component Visibility not working on Lightning Record Page

Question: This is a very simple scenario i am working on. There is a custom formula field and i need to hide 2 related lists 'Deployment task' which is VF component and 'deployment steps' which is a standard related list based on the formula field = Salesforce then show the related list. I am so shocked that this simple condition is not working when i set this up in component visibility filter. The components are being displayed no matter even though the filter is applied on lightning record page.
Any help on this is much appreciated. Thanks!
Comment: Hi and welcome to SFSE. Do you mean they never change visibility or do you mean they do not change visibility during edit, only changing after save? Could you please [edit] your question to show the formula and the visibility filter that uses it plus explain whether this is at all times or during edit. Thanks.
Comment: does the formula field's evaluation depend on inputs made to other fields on the Record Page?
Comment: @Himaja_Sfdc, I recently bumped into the same issue and after giving read access to the field it worked. Make sure your user has at least read access to the field.
Here's the document describes supporting data types.
https://help.salesforce.com/s/articleView?id=sf.lightning_page_components_visibility.htm&type=5
Answer: I assume you may be using the Filter Type "Record Field." If you use the "Advanced" Filter Type, select Record in the field section and then find the field you want to drive the filter; this should allow the related list to show when appropriate.
Answer: If this is not answered here is the article. It will only hide formula field with certain condition.
https://help.salesforce.com/s/articleView?id=sf.lightning_page_components_visibility.htm&type=5
These field types are supported:
-String type fields: Autonumber, Currency, Email, Number, Percent, Phone, Text, Text Area, URL
-ID
-Checkbox (boolean)
-Geolocation
-Picklist
-Formula fields that resolve to one of these preceding types
-Roll-up summary fields that resolve to one of these preceding types


Anatomically correct Gigantes

Question:
A creature from Greek Mythology; giants with legs that resemble snakes that fought the gods and Heracles in a war (not to be confused with the Titans). Is such a creature possible to make anatomically correct (I know snakes for legs is impossible, but could there be something that resembles it)?
Comment: Note that the Giants (= *Gigantes*, "Earth-born" in Greek) *do not* have snakes for legs in any Archaic and Classical poems and visual representations. (The Greek Classical period is the 5th and 4th century BCE; it is followed by the Post-Classical or Hellenistic period.) See many Classical representations of the Giants in the [Wikipedia article](https://en.wikipedia.org/wiki/Giants_(Greek_mythology)). The snakes for legs thing is Post-Classical, and even in Post-Classical times it is [far from universal](https://commons.wikimedia.org/wiki/File:Fregio_della_gigantomachia_02.JPG).
Comment: @Tortliena -- It may not be a duplicate, but there's no worldbuilding problem for us to solve either. Also, per AlexP's comment, the verbiage and the image don't match and the question therefore doesn't make sense. If it gets reopened without clarification, I'd VTC it for being unclear. Edits should clarify whether the query is about tritons (the image) or giants (gigantes is just a different etymological form of giants) or anguipeds as the body of the query indicates.
Comment: @Tortliena -- Possibly. This question has lots of other problems as well. One in specific is that the question *Is such a creature possible to make anatomically correct* is a yes/no. There is no fictional world context, no worldbuilding problem, if the picture depicts titans in stead of tritons, neither of those are giants. I'd still VTC for being unclear. Or maybe opinion based? I'd happily vote to reopen this question if it were edited to address something other than giants and if it were given some context.
Comment: @Tortliena --- As far as confusion: AlexP doesn't usually lead astray, but I'm willing to concede the possibility! But more, the marquee question only asks about "giants". Every culture has giants. If one is going to ask about "snake legged giants", then that ought to be the question. That's a simple edit for clarification. Pictures are always nice, but they need to be given context within the query. If I have to slog through thousands of images on google using multiple search queries and then have to research the context of the image, I'm not going to hold myself responsible for (cont)
Comment: What is the worldbuilding problem you're trying to solve? This series shouldn't be used to satisfy idle curiosity about mythological creatures.
Comment: The question's not a duplicate, because we're talking about snake-legged giants and not just giants. Therefore there's more than size, and even if only considering size, snake legs would give a big change on how tall they can go. Voted to reopen.
Comment: @Elemtilas Isn't "making a creature anatomically correct" a worldbuilding problem? Like... I don't know, [this one for instance](https://worldbuilding.stackexchange.com/q/221930/80336)?  Regarding clarity, the asker's question takes precedence on AlexP's comment. If a creature named Gigantes is for them a giant humanoid with snake-like legs, then why not? I mean, if their point of reference is the giants of 1st century BC with snake legs, it's their worldbuilding choice, not ours to make.
Comment: Also, please note that the picture is from wikipedia, which explicitly talks about a [specific depiction of titans during the gigantomachy](https://en.wikipedia.org/wiki/Giants_(Greek_mythology)#/media/File:DSC04529a_Istanbul_-_Museo_archeol._-_Gigantomachia_-_sec._II_d.C._-_da_Afrodisia_-_Foto_G._Dall'Orto_28-5-2006.jpg), not tritons (legendary siren-like creatures) or Triton (the sea god).
Comment: @elemtilas "Titan" was a misuse of words from me, they're giants. I've reworded the description based on what the ancient Greece Giants are, and revealed the underlying intent of the question. If you ask if a creature is possible in a given context (here more realistic), you're more than likely to want to add the creature in your world and make the work for that. Even if you're just "casually asking", knowing you can reasonably insert them into a world or not, is... Well, a worldbuilding issue, as per the reality-check tag. Otherwise all anatomically correct questions are out of order!
Comment: @Tortliena Where did you get the idea that OP wanted the critters to be tall enough to "Compete with the Gods"?, or the tallest version possible? We disallow edits that conflict with the intent of the OP. If the OP hasn't indicated that they want specific criteria than adding that criteria is on conflict with their intent.
Comment: @Sphennings It was perhaps poorly worded, but I still stand on my point. Because : A) They showed knowledge about what those Giants are, telling me that they want to match the depiction of ancient Greece authors, namely the later ones which tend to make them bigger. Also note that the giants fought the gods :). B) "**Giants** with legs". C) Are you implying that the persons who thought the question was a duplicate of "how anatomically correct can (non greek) tall giants be" were wrong in assuming the question was asking for tall people?
Comment: @Tortliena -- I'm not arguing that it was once quite possible that the OP was perhaps planning on maybe considering such a race for his fictional world. That, I think, is a good assumption for this forum! The issues are still two: 1. the OP presents us with a yes/no question, seeking an opinion, not a worldbuilding problem to solve; and 2. the OP is unclear as to what actual creature he's dealing with. That this query was never edited by the OP might just mean that he didn't know about the earlier question and when this one was closed, found the earlier one useful and sufficient. (cont)
Comment: (cont) -- Now that we're two years out from the original question being closed, rather than mess around with this one, I'd suggest that, if you really believe there is something distinct about this question that can not be answered by the other question, you should write your own question! I like anatomical queries, and if you wrote a non-duplicate query about giants, I for one would love to have a go at answering!
Comment: @elemtilas I'd suggest then to look out for reality-check questions, because they're meant for "yes/no answers" :). Doubts have been raised regarding legs, like other reality-check and anatomically correct questions did. Regarding the creature being unclear, you're misguided by AlexP's comment, which only notes that it's not the most common description of giants. If having a picture and a mythological reference is not enough for you, then I guess it's time to make a pass on reality-check questions, because some like vampires or medusa only make a brief description, skipping variations.[...]
Comment: [...] Now asking a new, better question about snake-legged tall people, specifically asking about legs is raising a curious conundrum : Would it be closed for being a duplicate of this question...? I guess it would be (basically the same essence), but then what about the original duplicate x)? It's something to think about.
Comment: @Tortliena --- Good point about reality check! Indeed those are yes/no queries, and they're designed to be answerable here. ***BUT!!!*** The querent has to provide the description of the creature or scenario! *Are giants possible?* is not a reality check query. While *I have an Earth-like world with ordinary Greek heroes: are giants as depicted in this frieze, with snakey legs, a realistic addition given the reasonable evolutionary history of this alternate world* most certainly is!
Comment: (cont) --- passing on reality check queries! I'm going to VTC and ask for clarification! If you asked a better question about snakelegged giants, I wouldn't VTC it as a duplicate of this closed query. Closed questions are closed. I'd only look to see if your new query is a duplicate of the query this one is a duplicate of!
Answer: I would say you just have to think about these creatures a little differently to make them work. If they were primarily aquatic, water will support vast amounts of weight and snake-like appendages might even be favorable as a means of propulsion in water. They would be incredibly fierce in the water, like giant octupi, but with bones they could still awkwardly haul themselves onto land. To a hellenistic world, an intelligent whale-octopus would be like a god. Think Moby Dick with tool using.
Comment: Bravo! This is a very good answer.
Answer: I'm not 100% sure what you mean by "anatomically correct", but I'll give you my take on it.
Let's consider what we see in the image: the whole body, except for the legs, is human. This means that all vital organs are still in the same spot. Most systems would still work exactly the same as a human: respiratory is unaltered, digestive, urinary, reproductive, none is heavily affected by this (we can clearly see their reproductive organs and their butt, so it's safe to assume everything works as intended).
They could as well be double amputee and all of that wouldn't change.
Now let's focus on what's different: their legs are covered in scales and shaped like snakes.
The scales are the main "anatomical issue" I see. A creature with scales would have most of its body covered by it: think of crocodiles or snakes (since that's what they are). You would only find softer skin on their abdomen (belly), but it would still be very different from human skin. So for it to be "anatomically correct", you would need most of the body to be covered in scales, much like the reptilians we see in many fantasy and sci-fi movies, OR have those legs be covered in human skin (which also implies hair).
As for the shape, while I don't see the evolutionary benefit of having two snake-like tails instead of your legs (it would work best either having only one larger tail, kinda like Medusa had, or several appendiges working similar to an octopus tentacles), it's not necessarily an anatomical impossibility.
This would obviously imply a big difference in both your muscular structure and your nervous and cardiovascular systems, but not necessarely impossible (again, very unlikely something evolved this way, but that's not the point).
The last question becomes "How would you move around?". Having two appendiges kind of implies you alternate one to the other, just as we do by taking steps with our legs. It would look very weird and probably less stable than a human walk, but it could work.
It's very unlikely, especially if covered in skin instead of scales, that you would slide similarly to how a snake does. On the plus side, it would most likely improve your swimming capability.
Hope it helps.
Answer: Realistically, giants of any kind are probably not possible. This is because of the square-cube law. This says that if you take a regular person and scale them up by double, they're not twice as big... they're twice as long. Instead their volume will be about eight times larger. This is a problem, because all of your bones have gotten twice as big (and can support twice the weight) but your actual weight is about eight times what it was previously. If you grow your creatures too large, and they "look" like they did before you inflated them, their bodies will be too large to support their own weight.
This leads to a lot of the phenomena we observe about large and small creatures. Ants can carry hundreds of times their own body weight. Fleas can jump the equivalent of a 10-story building. On the other end of the scale- elephants can't jump. If you drop an elephant from a height of 12 inches you will shatter every bone in their legs. The largest creatures on earth, whales, don't have to support nearly as much body weight as their land-dwelling counterparts. If you put a whale on land it will suffocate under its own weight.
Consider a rectangular prism, that has a depth D, a width W, and a height H.
The length of the cuboid is the maximum of D, W, and H.
The volume of the cuboid is D*W*H.
Suppose an average man is two feet wide, one foot deep, and six feet high. Their length is 6 feet, but their volume is 12 cubic feet. If we scale that up by two, then they're four feet wide, two feet deep, and twelve feet high. Their length is 12 feet, but their volume is 96 cubic feet. If we double the size again, then we have a giant that is eight feet wide, four feet deep, and twenty-four feet high. Their bones and other body structures are designed to handle weight that is four times the original man, but the giant's body weight is 768 times their original weight.
So any giant thing that looks like a regular size thing is generally not physically feasible, no matter what you're talking about.
But that doesn't mean that giant things aren't feasible, we build skyscrapers and things like that every day. They just have to respect the square-cube law. Some tips for building giant things:

Use super-strong materials, expressed as tensile or compressive strength. We don't build skyscrapers out of wood, we build them out of steel. Steel has an incredible strength-to-weight ratio. Steel is roughly six or seven times stronger than wood is given the same amount of mass (and steel is much denser, so the volume of mass there is much smaller). Carbon nanotubes are roughly 125 times stronger than steel given the same amount of mass.
Make things thicker on bottom than top. The bottom of a structure has to carry all of the weight of the structure above it, while the top only has to carry the weight of the top. Even in people, your thickest and most substantial bones are in your legs because your legs carry all of your weight. Many buildings, even if they look uniform on the outside, have stronger and thicker structural elements at the bottom than at the top.
Supercharge your creatures. Dinosaurs grew much larger in their time than we do today, because resources were plentiful and the atmosphere had a higher oxygen content. This allowed more efficient metabolism and bigger total growth. There are many theories as to why "megafauna" evolve and thrive when it seems clear that smaller size is a clear advantage in numeracy.
Lighten the load. You could reduce gravity on your planet, so larger everything can happen. (This is maybe a cop-out, because then your people would be larger too, so your giants wouldn't be as giant.)

So, what do you need for snake men? You need great big legs with big bones in them, perhaps more than two (more like an octopus). You have a smaller torso with skinny arms on top, though your snake men still need to be able to throw their body weight around and exploit their size. Maybe you could have metal skeletons or something too.
Answer: The only way I could think of a creature like this evolving is if it is either extraterrestrial, or from another dimension.
This is because, with the exception of conjoined twins, there are no organisms on Earth that have two or more heads.
If this creature isn't from Earth however, I do have a good idea. It's feet could actually be highly evolved mouths, that the Gigantes uses to eat.
Comment: they have only one head... jsut snake-tail legs.

Anatomically correct Gigantes


What exactly is a web framework?

Question: Is a web framework, such as Django and Ruby on Rails, simply a way of displaying code that could be written normally over http? Or is it used for more server side things, such as storing data. Is it used as a front-end or back-end for websites?
Comment: It sounds like you should be asking more about what is an MVC Architecture. Both Django and RoR are MVC frameworks. Understanding the role and purpose of using an MVC architecture will help answer your question.

http://en.wikipedia.org/wiki/Model%E2%80%93View%E2%80%93Controller
Answer: Let's talk for a moment about things that aren't a web framework.
At the most basic level of the web you have a webpage. It's typically a dumb page with some text on it, maybe an embedded video or a few images. It doesn't (or at least ideally shouldn't) care where the stuff it displays is coming from. You don't need any scripts, databases, etc. in order to have a static webpage. Typical tools used: HTML, CSS, Javascript.
Then you have content management systems (CMS) such as, say, Wordpress. They add a bit more functionality to your site, but really all they do is provide you with a way to manage your collection of webpages -- create ones on the fly, etc. You can use them as is and interact with CMSs through the administration pages they provide. You can extend some of them (for example, Wordpress has a plugin architecture), but you're typically not concerned with how they work or with their specific API.
And then you have web frameworks. They allow you to do everything else in a structured manner. You don't need to have a framework to create a database-powered site, but it can help. Frameworks buy you a lot of convenience through convention. For example, if you want to add a new section to your site, you can create a "module", upload it to a known location, maybe update a config file, and it more or less wires itself into your site.
The framework is what can take care of your database details or pulling data in from other services (or providing data through a service). It can build pages for you automatically based on a template. It can take care of "prettifying" your links through URL routing. It can help you make sure none of your site links ever break -- by dynamically figuring out where pages are instead of you manually hardcoding links. They allow you to separate your back-end concerns (business logic, data access, authentication, etc) from your views, allowing you to easily update your page design if you feel like it.
To specifically address your questions...

Web frameworks generate HTML pages served over HTTP. There's no particular magic here. You could often write the same pages yourself, but frameworks allow you to, for example, define a template and have a different page displayed based on your needs without your direct manual involvement.
Web frameworks don't store data. They can access or provide it, but they aren't themselves a database of any kind. Web frameworks live on the server side and serve up pages to the client and process client's input.
Frameworks like Django and Rails are used on the back-end. There are other frameworks like jQuery that can be used to script client-side activities, but they aren't web frameworks in the same sense. Usually when someone says "web framework", they mean server-side.

Hope this helps.
Answer: A web framework is a programming environment that helps you build web sites and services.  They are typically focused on server issues such as database connectivity, URL routing, HTTP protocol implementation, HTML generation, forms handling, and so on.  Some will also help with client-side concerns such as helping your Javascript code work seamlessly with your server-side code.
Answer:
A web application framework is a software framework that is designed to support the development of dynamic websites, Web applications and Web services. The framework aims to alleviate the overhead associated with common activities performed in Web development.

Taken from this page.

What exactly is a web framework?


using data-transformation for the data which has too many zeros

Question: I do a ANOVA, when I do the normality test, the data has too many zeros, how to make the data to normality using the transformation?
Comment: Welcome to CV. You might want to consider expanding the question from asking about a transformation to asking about more appropriate models for zero-heavy data.
Comment: Thank you!@DJohnson, so I can't do ANOVA with the data?
Answer: First, the data in an ANOVA does not have to be normal.  The errors (as estimated by the residuals) do.
However, when the dependent variable has a lot of 0's, the residuals will not be normal.
Second, no transformation  will get rid of excess 0s.  You can't use ANOVA on these data.  You should use a zero inflated regression such as zero inflated Poisson or zero inflated negative binomial.


Is there a relation between density and gravity?

Question: I often find this affirmation when scientifics reffer to black holes:
"A black hole is so dense that even light cannot escape from it"
Does this mean that there is a relationship between density and gravity?
For example, in the case of a black hole, why is it that its force of gravity is a lot more important than when it was a star (in the case of a star exploding and collapsing into its own weight to form a black hole) although the mass of this black hole and the mass of the star that formed it should be the same but in a different volume ?
Comment: Take a solid sphere of mass $M$ and radius $R$ and measure the gravity at a distance $x$ from the surface. Now consider the average density $\rho$ and volume $V = \frac{4}{3} \pi R^3$ to find how is gravity affected by mass $M$ and/or density $\rho$.
Comment: Here's a link to [Schwarzschild Radius Calculator](http://www.wolframalpha.com/widgets/view.jsp?id=15c7a7eb32c8610b005811b8640ebc1) that you might find useful and interesting. If our Sun was replaced by an equivalent mass blackhole, the gravitational effects on the planets and other bodies in the Solar System would remain just the same. They'll all continue to orbit the blackhole without spiraling down into it, but of course the earth would freeze in the absence of the thermal energy generated by the Sun.
Answer: Summary
Really gravity is causally dependent on the amount of matter(in fact energy) not in its density. There is a minimum density for a black hole but it is constant only for a defined amount of mass.
As objects of the nature of black holes are close to spherical instead of density it is more sensible to quantify a threshold radius, known as the Schwarzchild Radius.
The density of black holes makes an interesting quote because it is so extreme, but this effect can still be achieved with a quote like the Schwarzchild Radius of the earth is 9mm.
More
The amount of curvature of space-time (aka the strength of gravity) is related to the amount of energy in the space (this is both rest mass energy, kinetic energy and indeed energy in the electric field, vacuum energy$^1$, etc.)
At a point $r_p$ inside a homogeneous spherical body the effects of gravity due to all the energy in the body at $r>r_p$  can be neglected - they cancels out. Gravity is weaker inside a star (although there is a lot of weight of matter bearing down). In the centre of the star there is no net gravitational force.
Consequently a large body like your star doesn't at any radius achieve the gravitational strength necessary to create an event horizon. In fact for a given Mass the required radius that the matter must be contained in is the Schwarzchild Radius. For the sun, about 3km.
It's important to get all the mass below you so that it acts to increase gravity enough to cause an event horizon.
There is a relation between achieving the Schwarzchild Radius and a particular threshold density, but that density could also be achieved with a smaller mass and there would be no black hole.
This means for a particular mass there is a threshold density to achieve a black hole, if the mass and density are fixed and the object is spherical, which it will be under this kind of gravity, then the radius is known.
[1] This may be one of physics currently unsolved problems, as there may be a huge anomoly here - see "https://en.wikipedia.org/wiki/Cosmological_constant_problem"
Comment: I think I got it. So for example in the case of the earth, we need to have the weight of the earth (5,972 × 10^24 kg) contained in a sphere of a 9mm radius, so that it can create a sufficient force to not let even light escape from it the moment it enters the event horizon.
Comment: The mass of the earth - yes
 (not it's weight which is dependent on the gravity field strength the mass is in).


What factors are behind the recent increase in 2-D video games?

Question: I've noticed that recently there are considerably more 2-D games, especially of classic titles. Mario, DK, Kirby, and others for Nintendo, and no doubt other games for other platforms as well. What factors contributed to this increase of 2-D games in today's market?
Comment: Donkey Kong, excepting Donky Kong 64, has traditionally been a 2-d platformer. Kirby's the same way. Mario goes both ways.
Comment: The recent push in indie development probably has something to do with it, given 2D games are easier to develop.
Answer: Interesting question. I've actually been thinking a large factor is recent advances in 3D acceleration.
You may notice many of these games have 3D shapes, models or effects laid across a 2D plane. There's also an easier use of physics simulations thanks to 3D/2D interop.
Other considerable factors:

Development time of 2D games is often less for core functionality, allowing more time for all the bells and whistles to make very unique games.
Mobile games have caused an influx in 2D game developers which was followed up by an influx in mobile consoles, a favored 2D gaming platform.
"Classic Style" games with a 'new technology' feel are nostalgic for older gamers and generally pretty cool for everyone. New spins on old ideas.
Answer: I'd put my money behind:

the recent explosion in weak hardware with small viewscreens (how much can you really enjoy 3D on a 2x3 inch phone screen?)
revolution in ease of software delivery - AppStore et al makes it practical for individual developers to once again market software to users
it's easier and faster to program a 2D game to take advantage of point 2 than it is a 3D game
3D games require additional skillsets (modeling, physics, skinning) that 2D games do not
Comment: I am sure that it is #1 here that trumps all other suggestions.  Every other reason has been around for a long time, but the rise in small screen handheld devices... it dwarfs everything else.  It went from only people who purchased dedicated handheld gaming consoles (like gameboy, gamegear, etc) to *anybody with a phone*.  That's huge!
Comment: @Glen, true, that's a huge market. However, there are many new 2D games (or 2D-gameplay) coming to PC and consoles. I can think about many indie games, like Braid, Spelunky, Super Meat Boy, Aquaria, Gish, Osmos, World of Goo... Thus, I believe the ease of software delivery (Internet together with digital distribution systems like Steam, XBLA, Wii-ware, PSN) might be even more important than mobile devices.
Answer: Other users already gave great answers, but I also want to add my opinion.
I believe that, in many cases, the 2D gameplay is easier to understand, easier to play and easier to master than 3D gameplay. This is specially true for games aimed at casual players.

Most input devices are 2D (joysticks, keyboards, mice, touch screens...). Accelerometers are kinda 3D, but most time they behave as 2D input.
Video output devices are still 2D.

Even 3D displays are just two 2D images together, and not a true 3D space.

It is easier and a lot simpler to move in 2D space than in 3D space.
Moving in 3D space requires more input commands, which means more keys, more buttons or analog sticks, or a mouse and keyboard.

Sometimes we don't have so many input devices available (think about mobile games).
More input commands means the player must memorize more commands before mastering the game.

2D games usually don't have frustrating issues with bad camera placement.
It is easier to get lost in 3D space.

Note: when I talk about 2D, I'm also including games with 2D-based gameplay and 3D graphics.
Answer: Probably because the market demands them. I prefer to play 2D games because I get motion sickness when playing 3D games: headache, dizziness, etc. It is especially acute for first-person shooters, which I can't play at all. I'm sure I can't be the only one.
Comment: Have you tried adjusting the FOV and mouse speed?


Kali Linux screen recorder

Question: I want kali linux default screen recorder on my Ubuntu but don't know the name since I do not have the kali linux. The unique property which make me fall in love with it was the icon on the top panel appears once kali linux starts. I tried to find out the default packages of kali linux but everywhere only penetrating tools are listed.
Comment: You mean recordmydesktop? Check here: http://recordmydesktop.sourceforge.net/about.php
Comment: But record my desktop is not pinning itself on top panel (near to wifi, battery icons)
Comment: Well I guess it should be some configuration that you have to do.. I have never used a screen recorder, but as far as you see it in videos regarding Kali, that they use the same program, then it's probably a simple configuration on recordmydesktop program.
Answer: Here is someone's list of the top four Linux screen recorders and how to install them.  I hope this list includes what you are looking for.
Comment: It was kazam but I still don't kow how to pin it to panel.
Comment: But I found out similar vokoscreen with 'hide windows' option. I added it in startup program. Hoping it to appear with hidden windows on startup.
Answer: Getting the right Screen Recorder
Although Kali Linux has a screen recorder built-in, I would suggest getting a similar screen recorder that is very easy to install and customize. The name of it is "Simple Screen Recorder".
Why should you use it?
The name says it all. This is a simple screen recorder that can be fully customized to your needs.
Benefits of SSR:

SSR is multi-threaded
SSR is capable for Live streaming of videos
SSR supports many different types of codecs like MKV, WebM, MP4 etc
SSR can record on 32-bit OpenGL application within a 64-bit OS

How to Install SSR:
sudo add-apt-repository ppa:maarten-baert/simplescreenrecorder

sudo apt-get update

sudo apt-get install simplescreenrecorder

Answer: The one your talking about is "EasyScreenCast" it is a gnome extension and as @blametheadmin said it uses gtk-recordmydesktop which you can use from terminal or if you would like install jack2 qjackctl  and your good to go
Answer: I can recommend green-recorder.
Step to install through the command line:
sudo apt-get update
sudo apt-get install green-recorder
sudo add-apt-repository ppa:fossproject/ppa

Comment: Welcome *Any additional repositories added to the Kali sources.list file will most likely BREAK YOUR KALI LINUX INSTALL.*  [Kali sources.list Repositories](https://docs.kali.org/general-use/kali-linux-sources-list-repositories)
Comment: I'm not a Kali user, but why would you add a repository *after* (trying to) install the application?
Comment: You can update your system with unsupported packages from this untrusted PPA by adding ppa:fossproject/ppa

Kali Linux screen recorder


How does "tying the knot" on this cyclic linked list in Haskell work?

Question: I am learning Haskell and was reading through Tying the Knot on how to build a cyclic linked list. In the code
data DList a = DLNode (DList a) a (DList a)
mkDList :: [a] -> DList a
mkDList [] = error "must have at least one element"
mkDList xs = let (first,last) = go last xs first
         in  first
         where go :: DList a -> [a] -> DList a -> (DList a, DList a)
               go prev []     next = (next,prev)
               go prev (x:xs) next = let this        = DLNode prev x rest
                                         (rest,last) = go this xs next
                                     in  (this,last)

I am trying to understand the call where they link the last element to the first through a "little trick" (!) called tying the knot:
mkDList xs = let (first,last) = go last xs first

But I am having difficulty seeing how this works. What is "go" initially called with? And per the comment in the article, how is the first result from "go" "passed back in"?
Thanks!
Comment: Initially `first` and `last` are simply *thunks*, i.e. **unevaluated** expressions, the trick is that the `go` function does not evalute the arguments until their values are ready.
Comment: As an experiment, I tried to adapt the knot-tying code to Java in an overly literal way, using an explicit `Thunk` class instead of the "implicit thunks" of Haskell: https://gist.github.com/danidiaz/58cbbff4f4d4b6071b3daa2d54409292
Answer: Since Haskell is lazy, values are evaluated until strictly necessary. We can walk through a simple example using equational reasoning to see where that gets us.
Start with the simplest example: a one-element list.
mkDList [1] == let (first, last) = go last [1] first in first

It seems that you can't call go, because you don't know what last and first are equal to yet. However, you can think of them as unevaluated black boxes: it doesn't matter what they are, just that you can proceed with equational reasoning with them.
-- Just plug last and first into the definition of go
-- last2 is just a renaming of the argument for clarity
go last [1] first == let this = DLNode last 1 rest
                         (rest, last2) = go this [] first
                     in (this, last2)

Let's try to evaluate the next call to go in the same way.
go this [] first == (first, this)

Conveniently, we didn't need to imagine any new black boxes; go simply evaluates to its original arguments in a slightly repackaged manner.
OK, now we can go back the way we came, and replace the recursive call to go with its evaluation.
go last [1] first == let this = DLNode last 1 rest
                         (rest, last2) = (first, this)
                     in (this, last2)

And we'll plug this back into our original equation with mkDList:
mkDList [1] == let (first, last) = let this = DLNode last 1 rest
                                       (rest, last2) = (first, this)
                                   in (this, last2)
               in first

This doesn't look too helpful, but remember, we haven't actually called mkDList yet; we just used equational reasoning to simplify its definition a little bit. In particular, there are no recursive calls to go, just one let expression nested in another.

Since Haskell is lazy, we don't have to evaluate any of this until it is absolutely necessary, such as when we try to pattern-match against the return value of mkDlist [1]:
let (DLNode p x n) = mkDList [1] in x

To evaluate this expression, we just need to ask the following questions:

"What is the value of x?" Answer: we need to pattern-match against mkDList [1] first.
"What is the value of mkDList?" Answer: first.
"What is the value of first?" Answer: this.
"What is the value of this?" Answer: DLNode last 1 rest

At this point, you have enough information to see that x == 1, and last and rest don't need to be evaluated further. You could, though, pattern match again to see what, for example, p is, and discover that
p == last == last2 == this == DLNode last 1 rest

and
n == rest == first == this == DLNode last 1 rest

The magic is a call like (first, last) = go last xs first doesn't actually need values for its arguments; it just needs placeholders to keep track of what values first and last will eventually get when they are evaluated. These placeholders are called "thunks", and they represent pieces of unevaluated code. They let us refer to boxes that we haven't filled with anything yet, and we can pass the empty boxes to go safe in the knowledge that somebody will fill them before anyone else tries to look in them. (In fact, go itself never does; it simply keeps passing them along until somebody outside of mkDList tries to look at them.)
Answer: We can try some simple input first, to see what's going on there:
mkDList [1] = first
    where
    (first,last) := go last [1] first
                  = let { prev=last; next=first;         -- prev = last
                          x=1; xs=[] }                   -- next = first
                    in go prev (x:xs) next
                       = let this := (DLNode prev 1 rest)  -- a node is constructed, with
                                      -- the two pointers still pointing into the unknown
                             (rest,last2) := go this [] next
                                           = (next,this) -- rest := next
                                                         -- last2 := this
                         in  (this,last2)                -- first := this
                                                         -- last := last2

let in Haskell is recursive: same name can appear on both left and right sides of the equation sign, and will refer to the same entity.
First, go is called with last, [1] and first. Both last and first do not yet refer to any value; they exist only as identity, kind of "named pointers" to still empty boxes, boxes which are yet to be "filled" with values.
Going into the guts of go, both names are "fleshed out", and then the final value (this, last2) is returned; then the pattern (first, last) is matched with that value. This is how the last finally gets its value, even though it was used as a named identity inside the go invocations. This is what is referred to as the tying of the knot: imagine an arrow going "out" of last into the go invocations, coming back to it from the deep; and same with first; thus creating chains of equivalences:
    first := this = (DLNode prev 1 rest)
    last := last2 := this
    prev = last
    rest := next = first

The above follows a somewhat imperative view of Haskell's semantics as a single-assignment language. The := operator is used, as a pseudocode, to provide a visual clue to the fact that a value is calculated by the expression on the right, and is "passed" into the variables in the pattern on the left of the equality sign (when that pattern is matched with the calculated value).

In fact, the name "next" is no good, as we're just passing along the very first node all the way down, to be used as the last node's next node:
 mkDList xs@(_:_) = first where (first,last) = go last xs first

 go ::   DList a ->  [a]  ->        DList a -> (DList a, DList a)
 go          prev  (x:xs)            first =
    (this,                     last)        -- (this   , last   )
     where
     this                                 := DLNode
             prev   x    rest
     (                   rest, last)      := go
             this     xs             first

 go          prev     []             first =
                                    (first,  -- first --> rest of the last node
             prev)

This can be "described" by equivalent Prolog definition:
mkDList(    [X|XS], First) :-                 % mkDList( in, out)
  go( Last, [X|XS], First,   First, Last).    % go( in, in, in, out, out)

go(   Prev, [X|XS], First,   This,  Last) :-   This = dlnode(Prev, X, Rest),
  go(  This,   XS,  First,   Rest,  Last).    % fill the Rest, return Last
go(   Prev, [],     First,   First, Prev).

Indeed,
?- mkDList([1,2,3],X).
X = dlnode(_S1, 1, _S2), % where
    _S2 = dlnode(X, 2, _S1),
    _S1 = dlnode(_S2, 3, X).


Crepant Morphisms of Varieties

Question: Let $X$ and $Y$ be algebraic varieties over $\mathbb{C}$. I am repeatedly encountering references to crepant morphisms $f:X\rightarrow Y$. I have found several definitions of such a morphism, one of which is the condition that $f^*(K_Y)=K_X$. Is this generally accepted to be the meaning of a crepant morphism, or is this only the definition in some more restrictive context? Also, I would appreciate some perspective on why one naturally considers this class of morphisms.
Answer: Crepant stands for non-discrepant.  It's frequently applied to resolutions of singularities or birational maps (but can be applied more generally).
Let's start with the birational case, since that's where the history is.
If $f : X \to Y$ is birational, and $K_Y$ is $\mathbb{Q}$-Cartier, then $f^*(K_Y)$ makes sense.  In particular, if $nK_Y$ is Cartier, then $f^*(K_Y) = \frac{1}{n} f^*(nK_Y)$ by definition.
Write $K_X - f^* K_Y = \sum a_i E_i$ where we pick $K_X$ and $K_Y$ which agree where $f$ is an isomorphism.  The $\sum a_i E_i$ is then independent of choices.
Now, the numbers $a_i$ are called discrepancies.  If there are no discrepancies (ie, all the $a_i$ are zero (for example, if $f$ is a small map), then the map is called crepant.  Of course, all $a_i = 0$ if and only if $K_X = f^* K_Y$.
Of course, if the pullback of $K_X$ is $K_Y$, then this can be applied to many things.  The existence of a crepant resolution of singularities also can be quite useful.  Let me give a nonstandard example in characteristic $p > 0$, if $Y$ is Frobenius split and $f : X \to Y$ is crepant, then $X$ is also Frobenius split.  Some variant of this appeared in the work of Mehta-van der Kallen and also Mehta-Srinivas.
Comment: Dear PDC, I don't think the map you wrote down is birational.

A finite dominant birational morphism between normal varieties is automatically an isomorphism, is it not?
Comment: Suppose that the morphism $f:X\rightarrow Y$ is finite, dominant, and birational. Suppose also that $X$ and $Y$ are affine. Is it then automatic that $f$ is crepant? It seems to be the case for the morphisms $\mathbb{C}^*\rightarrow\mathbb{C}^*$, $z\mapsto z^n$.

Crepant Morphisms of Varieties


How can I identify the virulence factors in my FASTQ files generated from nanopore sequencing bacteria DNA?

Question: I have performed genomic sequencing using nanopore technology and upon analysing using BLAST in the command line I have identified the presence of E.coli. I was wondering if I can add some code to identify the known virulence genes of E.coli which are on the NCBI BLAST database? Thank you.
Comment: If you could kindly try to improve the question unless @pippo1980's answer is helpful. This is not a clear question because you appear to be asking a very specific question for undefined code for a database we don't seem to be aware of, i.e. a NCBI virulence factor database. It's not that it's not solvable - but without further information its really hard, e.g. present an example of the Blast result you want to explore.
Answer: you could try to submit your sequences to VFDB: a reference database for bacterial virulence factors ; paper here : reference paper.
use the VFanalyzer tool

VFanalyzer provides an automatic analysis pipeline for a systematic screen of known/potential VFs in given complete/draft bacterial genomes. Users can perform the analysis by one of the publicly available bacterial genomes either from our pre-downloaded genome list (Option 1) or via any valid GenBank accession(s) (Option 2). Or alternatively, users can also analyse any private genome data (raw FASTA sequence, predicted proteins, or annotated GenBank format genome) using Option 3. For query with raw FASTA genome, predicted CDSs will be identified using GLIMMER3 prior to the run of VFanalyzer.
Please note that, VFanalyzer only accepts query genomes from the genera of bacterial pathogens with full information in VFDB, and it's designed for complete or nearly complete draft genomes. So you are at your own risk if the query genome are derived from other bacteria or only partially sequenced.

NOTE: Due to connetion issue with NCBI, VFanalyzer can not fetch gbk file using Edirect correctly. Please download the file manually and use option3 to submit your jobs, we will find the other way to fix the problem ASAP.

Think you need to convert your FASTQ to FASTA first.
Other resource is : VirulenceFinder 2.0 or PathogenFinder 1.1;  paper ref : In Silico Genotyping of Escherichia coli Isolates for Extraintestinal Virulence Genes by Use of Whole-Genome Sequencing Data, PathogenFinder - Distinguishing Friend from Foe Using Bacterial Whole Genome Sequence Data


Size of Partitions in Partitioned Tables

Question: According to the following link, it is advisable to use hash partitioning when, "The sizes of range partitions would differ quite substantially or would be difficult to balance manually." This implies that when creating partitioned tables, the partitions should be relatively similar in size. Is this true?
Comment: There is no link in your post. Could you add it?
Comment: The quote is from the book Database Management Systems
By Rajesh Narang -- so the "following link" that was not listed is probably not useful.
Answer: Well, yes it's true.  One important reason for partitioning is to reduce the I/O load for queries.  That is, only one partition needs to be read for a given query.
If you make a bunch of assumptions, such as:

An even distribution of rows over queries over time (relative to the partitioning key)
Record sizes independent of the partitioning key
Equal access for the partitions

Then you will discover that for "n" partitions the most efficient solution is when they are equal sized.
That said, there are definitely special cases.  If the partitioning key is referenced through ranges (between), then hash partitioning is not optimal.  If some data is accessed much more frequently (such as the most recent data), then equal-sized partitions may not be suitable.  If you are using partitions for fast deletes (by dropping the partition), then hash-based partitions are not suitable.
Answer: Although it does not seem so, Oracle is not that smart(yet). When it can not predict which partitions will be used, the exec plan will be the same for every partition visited (with some exceptions on 12c).
So when stats are very different for every partition and the SQL visits them all, then the performance might not be optimal.
Also the number of partitions should be reasonable, when you create a table having tens of thousands of partitions, then access via a local index might be much much slower and then you end up with partitioned table having global indexes only. In such a case the partition drop implies a maintenance of globally partitioned indexes, and such an operation might be very slow. So at the end you loose most of the advantages of partitioned tables.
For example when you partition orders by creation date, they might be equal in size, but most likely the old ones will be already processed, while the recent ones will not. So it will be questionable whether the index on "processed" flag will be used for a query iterating over all partitions. In similar cases do not be afraid of row movement and sub-partitioning.
Answer: The first choice of what type of partitioning should be what are your goals for partitioning.  As Tom Kyte would say "PARTITIONING != FAST" -- although it can generally speed things up, particularly when queries would be selecting data from just a small fraction of the total rows, as Gordon mentioned in his answer.
If the primary goal is to easily archive old data, such as the typical customer_order table, range partitioning would be used; if it is partitioned by month, you can drop partitions containing data over 5 years old very easily.  You can also load the "last  month" activity from a non-partitioned table to a partitioned history table.
If your data is location-specific, then list_partitioning would be one approach, where each country's data were in different partitions, assuming that common data access would be by country.
Bottom line, is don't believe everything you read; read several sources such as Oracle's Database Concepts and Database VLDB and Partitioning Guide.
The Database Concepts lists the main benefits of partitioning as

Increased availability
Easier administraction
Reduced contention
Enhanced query performance

But again, you need to determine what makes sense, based on the business need, and be aware you can have composite partitioning - one level partitioned one way, and that level's partition data be also partitioned, using a different method.


Adding a measure to a filtered data extension

Question: I am trying to add a Measure to an existing filtered data extension, i basically want to send an email but exclude people who received 2 jobId's in Marketing Cloud. I've tried everything :(
Comment: I would highly recommend using SQL Query instead of Measures. Measures are notoriously inaccurate, hard to use and have odd scheduled updates of data they use (not real time). This combined with the fact that Measures are no longer supported and have not been updated or even touched in years, I would steer clear of them if possible.
Answer: I would advocate SQL as Gortonington says, but if you want to do this as a one-off and don't want to use SQL, you can do this (will take longer though):

Go to Tracking > Sends
For the two emails you're referencing, go to the tracking screen and export the sent lists, adding the subscriber key field at a minimum

Create a sendable data extension with three fields - SubscriberKey (make this the Primary Key and the field that relates to Subscribers on Subscriber Key), Sent_Email_A and Sent_Email_B (you can call these whatever you want). The latter two fields can be set as nullable.

Format each sent list in a spreadsheet editor adding the Sent_Email_A or Sent_Email_B column as required, then find and replace in the column with 1

Import your two sent lists to the data extension created in step 3

Filter your data extension where Sent_Email_A and Sent_Email_B are True (or 1 if you made those fields text rather than boolean).

You should now have a data extension containing subscribers sent both Email A and Email B, and can use it as an exclusion/suppression as necessary.


What is "Two system dialogs displayed" message?

Question: I was using the VO learning in System Pref and went away from my computer for a few min. My screen was black when I got back and I clicked the mouse to wake it. Then it went black again and I clicked the mouse to wake it again it said "Two system dialogs displayed ". What is that?
Answer: It is a feature of VoiceOver to alert you to the fact that system dialogs have been displayed (this text can be read by the computer voice for you).
You can find the dialogs by tabbing through the open windows (or if you can see sufficiently, they're probably already displayed on the screen).


Very very energetic puppy

Question: My puppy Mia is 1 year old and very energetic. She jumps and barks when she plays. and when you walk, she wants to play with you. I was concerned because my older boy dog, Mojo, did not act like that when he was her age. Is that normal for puppies?
Comment: Yes, high energy is normal for puppies, kittens, and children.
Comment: What breed of dog is Mia?  Some breeds are more energetic and playful than others, although in general this is totally normal for a puppy.
Comment: A tired puppy is a good puppy. Give her plenty of exercise: long walks, playing fetch, etc. Challenge her mentally through obedience training and dog sports like nose work.
Comment: Related [My dog is becoming unusually hyper. Whining, won't hold still, and jumping/nipping at me](http://pets.stackexchange.com/questions/13677)
Answer: This is very normal behaviour for a 1 year old dog.  Dogs are energetic and do like to play especially certain breeds.  I wouldn't be too disgruntled over it or worried.

Very very energetic puppy


About getting area from DEM below 5000 and below 3000 m elevation?

Question: I want to get the area from the DEM which is below 5000 and 3000. Actually I need those two areas for my Regression Model to calculate the discharge. In that case, how can I find out using python. I need to calculate in each cell of the stream segment. I have tried with Surface Volume tool but it is taking too long time as i need to calculate for all the cells along the stream segments. Is there any easy and fast way to get this information.
Answer: To extract cells below 5000 meters/any unit, you should use Con.
Write the SQL expression like "Value < 5000" (or change value to what you need).
This function can also be used in Python scripts.
Comment: Yes I have tried with that also but the problem in my case is I need to have watershed for each cell and use Con for that derived watershed which is taking too much time for whole stream... Can't I make it faster.. Is there a way to make those processes faster using Python.
Comment: Well, not exactly sure what you mean with "a watershed for each cell", you can hardly delineate catchment areas for every cell. Also, calling a function from Python doesn't make it run faster (at least not to any significant level). However, you can automate a >workflow< so you wont have to call each function manually.
In some cases there are tricks to make a function compute faster, like using in-memory workspace, but if you have a large DEM that might not be feasible.
Comment: I need to calculate discharge at each cell of the stream using data of area which is below 5000 and 3000. In order to do so, I am creating watershed at each cell and after that I am using Con() function to calculate area. This is taking too much time and crashes frequently what can be solution for this.


Syncing first person arms and enemy character for struggle in games

Question: Some FPS have it where your arms are struggling or doing something melee to a character model. Both the arms and the character you're interacting with are sync'd up in the animation. What's the general idea behind how that syncing is done?
Answer: In short, make sure the animations are in-sync when animated, so that you can easily play both animations at the same time. Some systems, like Mecanim in Unity, allow for transitions and so you would have to watch out that the transition does not blend too far in to the new animation. In the same way you'd want to play the animation instantly and not wait for another animation to finish first.
<code>initial animation --> struggle animation --> potentially branch to different animations
</code>
It's not too dificult to pull off, but of course requires that the enemy is correctly placed in front of the player. This offset should be the same as when the animation was done in Blender, for example. Generally you have a "root" or "world" object, which is used to position characters at their initial position.
Systems like Mecanim also have some more advanced IK controls, so you can place the arms relative to another point, so that the enemy wouldn't have to be spot-on.
Perhaps if you had a more concrete goal or animation that wasn't working I could guide you a little better. Images of what your character rigs look like as well would be valuable information.


stormy rainy window effect

Question: I'm making an indoor scene with a storm outside.
I want the windows in my scene to have rain just bucketing over them. Ideally I would like some animated effect that can be composited over the background, which might be something like a bokeh image. How can I achieve this?
Answer: A polygon-rich approach
I gave it a go with a shower of particles. This may be a little bit too resource-intense for just a background feature though.
The setup
I created a simple "room" with

a double-layered window (two plane meshes);

a plane out in the sky, almost vertical, with a particle system;

two strong wind force fields that push the particles toward the window;

a simple icosphere as a dupliobject.

The building and the inner window layer are set as Collision objects with "Kill particles" activated.
The outer window is a Collision object with very high stickiness (no kill), and high damping/friction on particles.
The particle system has strong Normal velocity and low Gravity field weight, so that the rain drops don't fall off screen too quickly; "Object" > "Icosphere" is selected as "Render" option, with "Emitter" un-checked.

(this preview is from an earlier version, with less particles and less friction on the surface)
The render
By giving the icospheres and window layers a Principled shader with very high transmission; adding some orange streetlamps and violet "dusk" sun (and a sad Suzanne in the storm); with some DOF and motion blur: this is a very rough result:

     (Only 7 frames)
Using nodes and a "Geometry" input, I made the raindrop's shader completely transparent (shadeless) when the "y" coordinate is less than y0 (the position of the window) to cut away the part of the sphere that "permeates" the first layer.
This answer's blend file

Even heavier for a close up shot (with metaballs)
If you want a close-up shot as in here, an additional Particle System with similar physics, but from a nearer plane (just near the camera) and with big meta-balls as DupliObjects, can help:

Result:
Comment: This is certainly an approach I can take, so I'll try it. Thank you! What bothers me about simulation approaches is that they work up from the ground rather than down from the impression you want. For example, unless you have an extreme close-up shot of the window, the individual drops are invisible: https://www.youtube.com/watch?v=3J40T2-lWZQ
Comment: Yes, I realize that obtaining a particular result with a simulation approach would require some intense trial and error. However, I'm uploading an updated version of my file and render
Comment: Anyway, given this footage, I would have two different particle systems for such a close up shot: one for the background with spheres and one for the window (particles falling almost vertically from very close) with metaballs
Comment: @dixiepig updated with an additional particle system, just for close ups
Comment: @dixiepig I was looking at my file and I can say that the wind is really too strong in my file, and it's also too parallel to the window; also, the friction on the glass' surface should really be high! My simulation looks a lot like a moving train

stormy rainy window effect


Permissions not copied from 2010 to 2013 in DB Backup

Question: I am upgrading from SP 2010 to 2013 using content database approach. The lists and content get moved but the user permissions are not copied? Am I missing anything?
Answer: Do not switch from Classic to Claims on SharePoint 2010. This is not the recommended approach as you then potentially have a non-working environment. Instead, create a Claims-based Web Application on SharePoint 2013. When attaching each content database (you can do this one at a time or all databases at once), simply run:
Convert-SPWebApplication -Identity http://webAppUrl -From Legacy -To Claims -RetainPermissions:$true

That will convert the users within the database from classic to claims.
This is the best approach as you will then be able to fall back to a known working SharePoint 2010 environment. If you convert to claims on SharePoint 2010 first, not only will it take longer, but you may end up with a production environment that unexpectedly does not function properly.
Comment: No one said you couldn't. I said you shouldn't and it's not best practice or as fast as performing the conversation on 2013.
Comment: Hi @Trevor I always trust your answer but based on my attached Microsoft article https://technet.microsoft.com/en-us/library/gg251985.aspx ,
 Microsoft said you can convert them to claims-based web applications within SharePoint 2010 Products, and then migrate them to SharePoint 2013.  and this is the first method that I have mentioned above besides the other supported scenarios. and I think this is the answer for missing permission , so should you provide me with any link that says the first approach is not recommended , where I provide a link that said both scenarios are supported! Thanks
Answer: It looks like you don't switch SharePoint 2010 classic-mode to claims-based authentication before you take the content database backup in SharePoint 2010.
So you should

Switch your web application to claims in your 2010-environment.
Backup your content database,
In 2013 environment create a web application with claims and restore the content database then attach it with Mount-SPContentDatabase cmdlet.

All the scripts requited to switch your web application to claims in your 2010-environment with detail steps at Migrate from classic-mode to claims-based authentication in SharePoint 2013
Meanwhile, you can switch the authentication mode after migrating in SharePoint 2013 environment as the following :

In SharePoint 2013 Create a web application with classic mode.
Attach the database to this web application.
Convert the classic mode to claims

All the scripts requited to Create a web application with classic mode and switch mode are mentioned with detail steps at Migrate from classic-mode to claims-based authentication in SharePoint 2013
For more Details about Upgrading process check upgrade process to SharePoint 2013
Some considerations

Based on Microsoft article both scenarios are supported , and based on @Trevor Seward the second approach is the best practice (thanks to Trevor Seward)
To convert from classic to claims it's recommended to use Windows PowerShell , it's not supported by Central administration UI.
Based on Microsoft After you convert a web application to claims-based authentication, you cannot revert it to classic-mode authentication. but there's some workaround like mentioned in this article to revert back.


Implementing Auto-Bidding Functionality with JSP/MySQL

Question: Currently working on a project and could use some advice for how to approach implementing an Auto-Bidding system for a web application similar to Ebay.
My issue is actually handling to 'Auto' functionality. On initial thought, I figured I could just do a MySQL trigger, however, I quickly learned triggers don't allow you to insert/update the triggering table.
The only other real solution I could think of would be handling this on the server side with Java, however, I could see this implementation having poor time complexity:
e.g.
The auto-bidding works in a way in where it creates new bid items 0.01 above any bid placed on the specified item by a different user, while the auto-bid limit has not been reached
If many users have auto-bidding configured this can iterate for quite a while, and at each iteration the system would be doing an update query and I would imagine this could get slow in any sort of production environment with real users...
Plus, if I did a server side solution, this means that when some given, unlucky user sends a one-time bid or configures auto-bidding, they will be waiting for the server to handle this work before getting a proper response.
While it would make sense in a scenario like this to just create a bid item corresponding the the highest auto-bid limit, I do need to run through this process of +0.01 back-and-forth to actual model an auto-system, unfortunately.
So, any ideas on a better way to go about this?
Answer: If you are the operator of both the auction and the autobidding system, you do not need any timer at all. The outcome is determined at the time you know all autobid limits and manual bids: the highest bid wins, tie breaker is usually the earlier bidding time (or whatever you come up with).
For your server, an autobid is the same as a normal bid, they just differ in how the user experience them. Your server only needs to know which bids exists and when they got added.
You can e.g. add and update the effective step bids every time an actual bid or autobid limit get changed. It doesn't even matter how long it takes to process it, the outcome will be the same. If 2 users e.g. add an autobid for $100k 0.2s before the deadline and one user adds a $101k bid 0.1s before the deadline, it will take you more than 0.2s to generate 10 million $0.01-steps. But to answer the most relevant question to most bidders, "Did I win and what do I need to pay?", you do not need to wait for the step creation process to end, you just need to look at the 3 bids and can immediately tell that user 3 wins and has to pay $100k and one cent.
Technically, you would not even need to store the steps in the database, since your serverside code could just generate those (determined) steps from the stored limits and bids every time someone wants to watch the detailed bidding process. This seems to not match your requirements though, but might be a feature. (You can call it "compression" or even "normalization").
To the user, you will obviously only show the resulting bids up to the current time. The client can autorefresh with a timer to make it more exciting (since, in contrast to you, he doesn't know yet who will win), but that is independent of your server side code.


Android Keyboard : managing Keyboard appearance / disappearance inside fragments

Question: I have an app that contains at some point a FragmentActivity. This FragmentActivity contains some Fragments (FragmentA, FragmentB, etc). On each of these fragments, there are one or more EditText.
I'm trying to handle the keyboard properly. I want to make the Keyboard appear or disappear whenever I want.
For Example, When the FragmentA is created, I want to open the keyboard on an EditText. Then, three options possible for the user :

He clicks on a button that goes to the next fragment
He clicks on the Action Send of the Keyboard(that does nothing (on purpose) but close the keyboard normally) and then he can click on the button from the view
He clicks on the back button of the phone. In this case, it closes the keyboard and then he can click on the button form the view.

My problem is, whenever the user closes the keyboard by clicking on the back button of the phone, Android thinks that he doesn't want to see the keyboard ever in the activity. So when the FragmentB is created, I can't programmatically show the keyboard (Using InputManager btw) on a EditText from this Fragment.
Then, a second problem is when i click on the edittext to get the focus, in Android 4.x, the keyboard shows again, no problems, but with Android 2.x, it's impossible to have the keyboard shown again even if the focus is on the edittext ! It's killing me.
It appears that once the user has explicitly close the keyboard with the back button in one activity (even a fragment activity), you cannot show it again.
Does anyone have a solution ? Maybe playing with the flags in InputManager ? I didn't get all of them and what they do.
Answer: Try this:
Show keyboard:
InputMethodManager inputMethodManager = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);
EditText view = getCurrentFocus();
inputMethodManager.showSoftInput(view, InputMethodManager.SHOW_FORCED);

Hide keyboard:
this.getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_HIDDEN);

Hope it helps ;)


What would cause a community to shun two kids

Question: The community is a small one about an hour away from the closest town and rural. The kids are siblings, a boy and girl. The world I set this in has people with magic abilities, but magic is completely hidden from outsiders, so this community has no idea that the kids have magic.The kids' family was the founding family in that community and their parents died in a freak accident. I need a reason for the community to be really hostile towards these kids.
Comment: Because they're geeks, and maybe slightly out on the autistic spectrum.
Comment: This question is about generating story ideas. That does not meet the standards of this site, so I have voted to close as _primarily opinion-based_.
Comment: Sounds a similar to Harry Potter !
Comment: Suspected involvement in the death of an even younger child should very quickly do the trick. Maybe their magic lead to them being suspects. e.g. they teleported to the area and disappeared the real culprit (to try and save the child, alas too late) soon after the incident and were found there, but anyone who doesn't know about magic would assume they couldn't have been there moments later unless they were there at the time it occurred. Of course that evidence is circumstantial so they got off, but everyone "knows" they did it so they are hated.
Comment: Or perhaps the kids are from a disliked culture (like gypsies in some areas), and it's only people from this culture who can do magic.
Answer: I'm not sure if your question is on-topic because Worldbuilding generally focuses on physical elements of worlds (the creatures, the landscape, the infrastructure, etc) as opposed plot elements. You may find better answers on the Writers Stack Exchange.

First, is this the right choice?
It is important to make balanced characters. The plot is ruined if the protagonists are powerful enough to solve every conflict right away. The lesser-known side of the "balanced" spectrum involves characters too weak or in situations too dire to identify with. By making a "pity-party" scenario in which these characters just lost their parents - and now everyone hates them - you may lose some readers.

On to the Question
Suspicion of Involvement
Perhaps the "freak accident" left both kids unscathed when it should have killed the entire family - such as an explosion. Some person decides that the kids might have had involvement, and the community, searching for answers, grows suspicious - maybe even hateful. This is not super likely but if some false evidence of the kids' involvement with their parents' deaths is planted (or evidence is misinterpreted) it may be possible.
Actual Involvement
What if the siblings did accidentally kill their parents, via magic? Unable to reveal their powers, while showing signs of clear involvement with the deaths, these kids will be seen as psychopaths.
No Deaths After All
Perhaps their parents aren't actually dead, unbeknownst to the community - and the kids are just really bad actors. The community perceives the kids as heartless.
Comment: Not only physical. Building large communities, nations, their customs etc is perfectly on topic. But this looks more like plot element. If some % of kids would be treated like that long enough to form a custom, then this custom would be something good for this site.
Answer: Perhaps they had grown tired of the Founding Family and the town takes the opportunity to take over their own government by exiling the kids. Perhaps the freak accident was a hidden assassination plot to take out the family and the kids weren't supposed to even live.
Answer: Notice This question seems to mark a border between Worldbuilding and Storytelling. Nonetheless when removing the story part we still have a Worldbuilding issue about societal rules and perceptions. Thus it is on-topic.
That said...

The answer is quite easy and can be given by referring to a social stigma that's been around since mankind can remember:
Make the siblings Twins
Twins are not normal. They are different and sort of a freak accident of nature proven by their very existence. They are seldom and seem weird and strange to others.
E.g. quoting Wikipedia (emphasis mine):

Many cultures have mythic or folkloric explanations for how twins are conceived. In Greek mythology, some twins were conceived when a woman slept with both a mortal and a god on the same day. One of her offspring thereafter had godlike qualities, and the other was an ordinary mortal, such as Heracles and his twin brother Iphicles. In several Native American cultures women avoided eating twin fruits like double almonds and bananas because it was thought to increase the likelihood of twins.

The excerpt points out a tendency towards perceiving twins as different, wrong, freakish which could hence serve as a reason to wanting to get rid of them.
Story-Note: Your twins being the children of the Founding Family would then counteract this common feeling as long as their parents were alive. Parents gone > no reason to not shun them.
Comment: @Zxyrra well I hope I have not insulted you accidentally in any way then. What I am bringing up as a *possible* reason here is a fear based on belief/superstition. The OP does not mention any particular time but mentions rural area as well as they being part of the *founding family* though. While the latter can be easily used as a reason, the former lends itself to use my proposed solution, as rural areas are often associated with simple minds and superstitions
Comment: As a twin I cannot say that there is stigma against twins in modern times; "freak accident of nature" or not it seems to have absolutely no effects.
Answer: Make the kids neurodivrgent. I speak from experience saying that while even though physical disabilities are  still common subjects of hostile ableism, with invisible disabilities an ableist will not be as averted by vanity.
There are several more possibilities than the examples that I'm giving, and more to the disabilities than I'm listing, but here's stuff to start out with. Keep in mind is that even people with the same disabilities will not necessarily have the disabilities in the same way. As well, source whatever research you can from people who have those disabilities- they know their experiences better than their mother, or some scientist.

Dyspraxia: This is a neurodivergency characterized by poor motor skills, sensory processing issues, executive dysfunction, and poor short term memory. A lot of this can be misconstrued as laziness. It's easy for a mean person to get mad at a kid for forgetting what they've just heard, or for not being able to handle strong scents, or having illegible handwriting. Other children might sneer at them for stuttering, and the adults dismiss it as kids being kids. In my personal case, the worst part of my dyspraxia was that I was hypersensitive to pressure and movement of my hands;I cannot write painlessly to this day. I had a lot of trouble in gradeschool for not writing; The teachers didn't believe I couldn't write, and made a point of how unreasonable they thought I was. I was treated like I was pretending, even though it really did hurt for me to write. My IEP wasn't followed without begrudging, and that was only when it was followed at all.
Tourettes Syndrome: This one is characterized by involuntary sounds and actions. Your protagonists might twitch their eyebrows, make noises, slap themselves in the face, or say things, all without intending to. This can be interpreted by a hostile observer as attention seeking.
Sensory Processing Disorder: This is where somebody is either hypersensitive, hyposensitive, or sensory seeking. Sensory processing disorder generally exists as a part of other disabilities, like autism or dyspraxia, but it also happens on its own.
Answer: How about religion? They have a dissaproved one, or do not have one, or maybe they are not extreme enough.
Another possibility is that their parents are not married or from different races?
Answer: Step 1: The kids need to be different from all the other kids in a way that doesn't scare the other community members, but makes them feel uncomfortable. Like David Bowie style eye colors or an unnatural beauty.
Step 2:Things happen around the kids. The community doesn't know about their magic and maybe the kids haven't (fully) realized it too.
Step 3: Other kids. Other kids can be real (if I'm not allowed to say, please edit out) assholes. They can be role model bullies and start bullying the two siblings. The siblings cause magic by accident, like telecineticaly throwing a knife at one of the bullies when most scared. The bullies run to the adults, adults question the siblings in a rough way, more accidental magic, adults get hurt, things are escalating and siblings are shunned from  the community.
Et viola.
BR
Alex
Answer: You did say they are orphans, right?
Dang, that was a short answer.
But wait, there's more!
The girl can talk to animals. She was always viewed as antisocial due to her habit of wandering into the woods for days on end, and even when she is in town, she doesn't play with the other kids, preferring instead to hold court with her entourage of woodland critters.
The boy is where things get more troublesome. His talents run more to the summoning end of the spectrum: demons. He isn't controlled by demons - much the opposite - but that doesn't mean some of their evil doesn't rub off on him, just a little. No enough to change his actions; but a miasma of evil hangs on him, just out of normal sight, where the townspeople can sense it subliminally and respond to it. Maybe they think he's evil; maybe they notice that other kids around him tend to give in to their darker natures more than other kids; maybe those kids who already have darker natures are drawn to him. Any way, all the townspeople know is that bad things happen around him, whether he's directly involved or not. Now, maybe he can control this leakage once he understands what is happening and gets some training; only time will tell.
Oh, and the siblings' psychic leak doesn't help the issue either.
But mostly, they're orphans.
Answer: Merge every reason you can think of:

Twins that look weirdly similar
They live in creepy mansion
Parents were rich and snobby; not even locals but some rich eccentrics from the city that wanted to live in a mansion
Parents died in freaky accident
Because of magic weird stuff happens around them: animals behave differently, lights go off and on etc.

=> Lonely orphan kids that no one is looking after => Creepy pale socially extremely awkward creepers
The kids can also do pranks. One of them could go horribly wrong and everyone would know or suspect those kids.
EDIT The prank does not even have to be bad, but something can happen. If a pregnant woman would end up as the victim of a prank and then gets a miscarriage, it would be extremely bad if it were to be linked to that prank. Add a suicide due to miscarriage and the mood of a small community is absolutely wrecked, which for there is those to kids to blame...


Weird Animation problem

Question:
As you can see in those 3 picture,i was using the record button to keyframe the animation and copy the rest pose to frame 77. I have no keyframe in frame 76 and things should go smooth from 75 to 77. But somehow the rig twisted like that in the middle picture.
The problem only happen when i copy pose, use the I key to insert key, and return to rest pose(Alt+R,Alt+G).
Edit 1: add the blend file
Comment: I see constraints.  The problem is probably not with any of the things you're mentioning, but with your constraints, which can cause interpolation problems very easily.  But to diagnose those problems, people would need to know how your rig was set up.  Best to link a file.
Comment: added the blend file
Answer: Okay, so the problem isn't with the constraints, but with the keyframes on "main".  On frame 75, main is keyframed to a quaternion with a W component of about -0.997, but on frame 77, its W component is 1.0.  That takes it through an entire rotation.
If you edit the frame 77 keyframe to set the W value equal to -1 instead of +1.0, it will stop rotating through the extra rotation on frame 76.
If your goal is rendering in Blender, this fix may interact poorly with some NLA (if you blend out the animation, or blend over an animation with a positive W.)  That's a solvable problem with extra strips to hold the W at negative values, but explaining it would probably require an actual example of the problem.  If your goal is game animation, it's probably not going to be an issue, as game engines tend to interpolate quaternions differently from Blender.  Unlike Blender, game engines are likely to use "shortest path" quaternion interpolation, which automatically removes issues like this.  (I wish that Blender could do the same thing, and hopefully, with some changes to how Blender handles quaternions that are already under discussion by developers, I'll get that wish.)

Weird Animation problem


How can Lagrangian method work whenever the Lagrangian is not convex?

Question: Let $$L(x,\dot x)=\frac{1}{2}m\dot x^2-\frac{1}{2}k(x-x_0)^2-mgx$$ the Lagrangian of a system. Euler Lagrange theorem says that a necessary condition to be a minimizer is to satisfy Euler-Lagrange condition. It's sufficient if the Lagrangian is convex. The method of Euler-Lagrange consist in finding solution of $$\frac{\partial L}{\partial x}=\frac{d}{dt}\frac{\partial L}{\partial \dot x},$$
and after, we say that the solution will give the minimizer. But since the Lagrangian is not convex, how can this method work?
Answer:
The underlying variational principle for EL equations is a principle of stationary action, despite that it is often referred to as a principle of least/minimal action.
Also note that Lagrange equations may not have an action principle to begin with, cf. e.g. this Phys.SE post.


SD card won't mount to Moto G

Question: I've had a 64g card in my phone for months now, then all of a sudden (I believe after I updated to Lollipop) I began to receive errors saying the card was unexpectedly removed even though it was still in my phone. So I've tried to remove it and put it back in while the phone was both turned off and on with no success. My external storage settings don't even show the card is in my phone. I'm not super tech savvy so I don't know how to reformat and all that. Any simple fix?
Answer: Unfortunately, reformatting the card seems to be the best option but may not help anyway. There probably isn't a simple fix. There's lots of guides on how to format an SD Card in FAT32 but I'll give a quick overview for a Windows PC. Please be aware that this will wipe all data from the SD Card:

Backup data from the card using Windows Explorer.
In Computer or This PC, right-click your SD card and click 'Format'. Make sure FAT32 is selected and then confirm the operation.
Power off your device and insert the SD Card.
When the device boots, it should (hopefully) recognise the SD Card.
Comment: OK, awesome. Post back here if you need further help!

SD card won't mount to Moto G


What's a good way to refer to all four sites collectively?

Question: Now that Stack Overflow has become a group of four sites (Stack Overflow, Server Fault, Super User, and now this meta site), what's a good way to refer to the complete group? Is there an official name?
Comment: I have just realized how good this question is lol. It would be really nice to have official name, made by community :)
Comment: Related: *[Stack Exchange Glossary - Dictionary of Commonly-Used Terms](https://meta.stackexchange.com/questions/40353/stack-exchange-glossary-dictionary-of-commonly-used-terms)* (for instance, search for "Super User")
Answer: The Trilogy. Obviously. After the many books in the Hitchhiker's Guide Trilogy.
Comment: Indeed the fourth book has the comment "The fourth book in the inaccurately named Hitch Hikers Guide to the Galaxy Trilogy" and the fifth has "The fifth book in the increasingly inaccurately named..."
Comment: It doesn't seem fitting to refer to websites as a "trilogy", though.
Answer: The best way to refer to the trilogy is, of course, with a regular expression:
S[OFU]

Pronounced "ess oh eff you", naturally.
Comment: I thought SOFU rhymes with tofu.
Answer: Isn't it already called the Stack Overflow Trilogy?
But if an abbreviation is key, SOFU could work
Comment: Definitely this one (trilogy), ala Hitchhiker's Guide "trilogy"
Comment: SOFU? I think many people might mistake that as an abbreviation for something else.
Comment: Quadrology perhaps.
Comment: SOFU - and if you want to include Meta, then SOFUM.
Answer: M?S[OFU]

because we can parse the trilogy with regex, even if it's made up of HTML.
Comment: This answer needs 3900 votes, NOW!
Answer:
SO/SF/SU/Meta
My addiction
The Stack Overflow family
Answer: The Super Stack Fault Tetralogy. (That's what I'm going to call it, anyway.)
Answer: S*

or maybe
S?

I'd like to think that most of the users of these sites either already know what a wildcard is, or could be taught easily.
Comment: S? would seriously make the most sense... but no one would understand it and it would be confusing for SEO, etc.
Comment: S* would be more widely understood, if less accurate
Answer: The Four Horsemen?
Stackapalooza?
Comment: I like Stackapalooza, if only as a joke.
Answer: (The) Stacks
Answer: Stack Overflow site family?
Stack Overflow is still the first site. The commercial version of this web application is called by it, so... there is also so-family tag.
EDIT:
Stack Family?
Comment: Calling it the site family makes sense, however it's a bit long, and a bit clunky in some situations...
Answer: Well, they call it the Stack Overflow Trilogy on the blog. But I have no idea how you'd include Meta in that group.
Comment: Some folks prefer red heads you know.
Comment: Meta is the redhead stepchild.
Answer: The Atwoods Family (TAF, speak "tough")
Answer: The Increasingly Inaccurately Named StackOverflow Trilogy
Answer: I call it simply Jeff's :)
Meta User Super Server Stack Overflow Fault when I want to explain it to my colleagues :)
Answer: Stack-Tip Downwash
Only a suggestion.
Answer: For me:
Stack Overflow is dev
Server Fault   is svr
Super User     is usr
Meta SO        is alt

and if you think about it, each of them are just variants of CODEMONKEY!!!
So I vote for The CODEMONKEY COMMUNE
Why Commune? I give you the top 3 results on Wikipedia's disambig page for Commune:
Commune may refer to:

Commune (intentional community), a community in which resources are shared
Commune (socialism), a leftist model for society
Commune (card game), a poker-based bluffing game

Also if you haven't heard it yet, you may want to hear the Code Monkey song by Jonathan Coulton. Just don't go overboard and adopt it for an anthem or anything.
Answer: 3.1 (like 5.1 Surround Sound)


What does 思いっきりどうぞ mean?

Question: I heard this phrase a few times but I still can't grasp its meaning. Does it mean, "as much as you would like"?
Comment: Or maybe if you had been very rude to a fine lady and as an attempt to apologize you hold out your face and say "go ahead, slap me as hard as you want"  思いっきりどうぞ  .. *SLAP!* :P
Comment: That meaning is ok, IMHO, but usage, may be boxing trainer will tell you that.
Comment: And, I think `好きなだけどうぞ` is more common than `思いきりどうぞ` with similar meaning.
Answer: You can translate it as "Knock yourself out". It means "Go ahead and do that thing, if you want to". Sometimes it's said sarcastically, as if the thing the other person wants to do/try isn't going to work out. Sometimes it's just used as "Please, go ahead", without a sarcastic tone. If there is an exclamation mark after it (or the spoken equivalent) it's probably sarcastic.
I usually see it written as 思い切ってどうぞ.
Comment: @flamingspinach: 思いっきり with っ for emphasizing may not be listed in all dictionaries.  思い切り or 思いきり should be in a dictionary, though.
Comment: +1: And thanks, I was trying to construe this as a slangy variation of 思いつく and getting nowhere.
Comment: You can find 思いっ切り in a dictionary, I think. It's certainly related to 思い切る and not 思いつく.
Answer: 思い切る, as you might guess from the letters, literally means "to stop deliberating/thinking". It can actually have two meanings: "to give up", or to "decide". That said, when it's used as 「思いっきり」, it always means to do something decisively, with gusto and without reservation.
思いっきり has been idiomatized to the point that it no longer necessarily modifies a verb; it can serve to emphasize an adjective as well: 「彼は思いっきり弾けた人格だ」(he's got a extremely spontaneous personality).
Answer: I like the translation "absofuckinglutely go ahead", but that might be too casual (in English) for what you're looking for.

What does 思いっきりどうぞ mean?


Proof that the triangle formed by mass centers is equilateral.

Question: Let $ABC$ be a triangle and consider $A_1$, $B_1$, $C_1$ outside the triangle such that triangles $ABC_1$, $BCA_1$ and $ACB_1$ are equilaterals.
Consider now $A_2$, $B_2$ and $C_2$ mass centres of $BCA_1$, $ACB_1$ and $ABC1$, respectively. Prove that triangle $A_2B_2C_2$ is a equilateral triangle.
Answer: I am working with $A,B,C$ are oriented clockwise, so you can make a sketch. We have $A_2=(B+C+A_1)/3$, $B_2=(A+B+C_1)/3$, $C_2=(A+C+B_1)/3$.
We want to show that if we rotate $\overline{B_2C_2}$  an angle of 60 anti-clockwise we get $\overline{B_2A_2}$. In other words want to show that $R(C_2-B_2)=A_2-B_2$, where $R$ denotes the operation rotation by 60 degrees(wrt origin), note this is a linear map .
Let's compute \begin{align}R(C_2-B_2)&=R(\frac{C+B_1-B-C_1}{3})=R(\frac{C-B+B_1-A+A-C_1}{3})\\
&=\frac{R(C-B)}{3}+\frac{R(B_1-A)}{3}+\frac{R(A-C_1)}{3}
\end{align}
Now, note that $R(C-B)=A_1-B$,  $R(B_1-A)=C-A$ and $R(A-C_1)=B-C_1$ because $BCA_1$, $ACB_1$ and $ABC_1$ are equilateral.
We get
\begin{align}R(C_2-B_2)=\frac{A_1-B}{3}+\frac{C-A}{3}+\frac{B-C_1}{3}=\frac{B+C+A_1}{3}-\frac{A+B+C_1}{3}=A_2-B_2.
\end{align}
This is what we wanted to prove.
Comment: +1..................
Comment: I need a 5th grade proof using only elementary geometry
Comment: This is called Napoleon's theorem, I bet you can find geometric proofs if you search for it. But the proof I gave is understandable for anyone as long as you admit that rotation of sum of vectors is a sum of the vectors rotated. Anyway, good luck.In fact, If you draw the vectors I use would be very enlightening.
Answer: Consider the compositions of rotations $I= R_{A_2,120^\circ}\circ R_{B_2,120^\circ}$; note $I(A)=B$. Let $S$ be the point such that oriented angle $\angle(SB_2,B_2A_2)=60^\circ$ and oriented angle $\angle (B_2A_2,SA_2)=60^\circ$. We have:
$$I=R_{A_2,120^\circ}\circ R_{B_2,120^\circ}= S_{SA_2}\circ S_{A_2B_2}\circ S_{A_2B_2}\circ S_{SB_2}= S_{SA_2}\circ S_{SB_2}= R_{S,240^\circ}.$$
Therefore, $R_{S,240^\circ}(A)=B$, so $SA=SB$ and oriented angle $\angle(SA,SB)=240^\circ$. Now we conclude that $S=C_2$. So $\angle(C_2B_2,B_2A_2)=60^\circ$ and $\angle (B_2A_2,C_2A_2)=60^\circ$, hence $\triangle A_2B_2C_2$ is equilateral.
Comment: +1...............
Comment: I need a proof for 5th grade. You can't use rotations or this kind of abstract tools


What's the difference between a sonar and ultrasonic sensor?

Question: After having read the introductions of the Wikipedia articles about "sonar" and "ultrasonic sensor", it is still not clear to me what the differences between the two are. In the context of robotics, is there any difference between these two sensors (terms)?
Answer: Sonar, as used in robotics means having an ultrasonic emitter and and ultrasonic receiver. There are also some sonar with a single emitter/receiver.
However, they all use ultrasonic sound waves to sense the distance to an object. Well, actually they really sense the time between the emission of the ultrasonic wave and the reception of it, which is proportional to the distance to the object.
I am sure that there are sensors that are true ultrasonic sensors in that they are used only to detect ultrasonic "sounds." For example, if you wanted to detect some of the sounds made by marine mammals, you need to be able to detect ultrasonic waves. I might call this an ultrasonic sensor.
However, since I don't study marine animals, I use "sonar" and "ultrasonic sensor" to mean the same thing.
Answer: Ultrasonic means above audible range,
Sonar may be within the audible range
In my opinion the ultrasonic being more precise also may come with higher price.
Comment: Welcome to *Robotics* Naguesh. Thanks for your answer but we are looking for comprehensive answers that provide some explanation and context. Very short answers cannot do this, so please edit your answer to explain why it is right, ideally with citations. Answers that don't include explanations may be removed.
Answer: The main difference is, SONAR (originally an acronym for SOund Navigation And Ranging) is used underwater and uses low frequency sounds (100-500Hz) as well as high frequency sounds (ultrasound, etc).
Ultrasonic sensors are used mostly over the terrain and limited to high frequency sounds.
Answer: In terms of functionality, an ultrasonic sensor performs a single distance measurement in a given direction (strictly speaking, such a sensor emits a sound cone, the angle of which depends on how the sensor is implemented).
A SONAR, on the other hand, seems to generally refer to a device that performs aggregated range measurements, i.e., a 360 degree scan combining many single distance measurements.
Similarly, a LIDAR combines many single laser distance measurements.
Answer: SONAR was to find submarines under water. It used low frequency sound that was readily conducted by water. The sound was audible and could be heard. Similar to RADAR with SONAR the sound reflected from the submarine and the delay in the return allowed to determine the range or distance to the target. The emitter and microphones were directional and allow you to determine the bearing or direction to the target.
The low frequency sound did not work well in air and the emitter and microphones were not very directional. so newer versions where developed that used high frequency or ultrasonic sounds, beyond the frequencies humans can hear. These were more directional and worked better in air that older audible sonar.
More solid state emitters, microphones, and microprocessors have greatly lowered the cost making them common for small mobile robots to detect obstacles.


How do you solve $\frac{x-1}{\sqrt{x}+2}=\frac{5}{2}$?

Question: I solved it using the quadratic formula and it went like:
\begin{gather}
\frac{x-1}{\sqrt{x}+2}=\frac{5}{2} \\
2(x-1)=5(\sqrt{x}+2) \\
2x-2=5\sqrt{x}+10 \\
2x-12=5\sqrt{x} \\
4x^2+144-48x=25x \tag*{(squaring both sides)}\\
4x^2-73x+144=0
\end{gather}
Then do the usual stuff and the solutions are $16$ and $9/4$. However $9/4$ doesn't work when you apply it to the initial equation. Is that solution correct, if not, where is the mistake?
Comment: Hi Hubert. Welcome to MSE. Can you please format your question using LaTeX?
Answer: If you rewrite the equation as
$$
2(x-1)=5(\sqrt{x}+2)
$$
and then as
$$
2x-12=5\sqrt{x}
$$
you can immedately notice that a necessary condition for a solution is $x\ge6$, because the right-hand side is positive.
With this side condition, you can square: $4x^2-48x+144=25x$, which indeed has the roots $16$ and $9/4$, but the latter fails to satisfy the condition.
Indeed, if you substitute it in the left-hand side you get $9/2-12=-15/2$, while the right-hand side is $15/2$.

A different strategy could be to set $t=\sqrt{x}+2$, with the condition $t\ge2$, because $\sqrt{x}\ge0$. Then we have $x=t^2-4t+4$ and the equation becomes
$$
t^2-4t+3=\frac{5}{2}t
$$
or
$$
2t^2-13t+6=0
$$
that has roots $6$ and $1/2$. Only the first one is good, whence $\sqrt{x}=4$ and $x=16$.
Comment: Thanks, that's what I couldn't figure out.
Answer: If you do your derivation backwards (reading bottom to top) and take the square root of $25x$,
the previous line would be $\pm5\sqrt x$.
$\dfrac94$ is a solution of $2x-12=-5\sqrt x$.
That's why you always have to check that the solutions you get are valid.