Glue morphism of schemes defined over irreducible components

Question: Let $k$ be an algebraically closed field and $X, Y$ be quasi-projective $k$-scheme.
Let $X_1, X_2$ be two irreducible components of $X$ and $f_i:X_i \to Y$ be morphims such that $f_1|_{X_1 \cap X_2}=f_2|_{X_1 \cap X_2}$. Then, does the morphisms $f_1$ and $f_2$ glue to a morphism $f:X \to Y$ such that its restriction to $X_i$ is $f_i$?
Comment: @user45878: you have to be careful. Irreducible components are typically taken to have the reduced induced structure on them (this is the only canonical scheme structure on them, even if $X$ is nonreduced!). Therefore, $X = X_1 \amalg_{X_1 \cap X_2} X_2$ can only possibly be true if $X$ is reduced. Similarly, one has to specify what scheme structure is taken on $X_1 \cap X_2$, and if one takes the 'wrong' scheme structure it is easy to come up with counterexamples.
Comment: I think that the answer is yes, essentially because $X$ is the fibered coproduct of $X_1,X_2$ along $X_1 \cap X_2$. In any case we can reduce to the case that $X$ is affine, then the corresponding diagram in the category of rings is a pullback diagram and its universal property gives the answer.
Comment: Yes. Recall that a morphism between schemes is simply a morphism between the underlying locally ringed spaces, so no algebra is involved and no hypotheses are needed on $X$ and $Y$ other than they are locally ringed spaces. Just set $f$, as a map between locally ringed spaces, to be $f_1$ on $X_1$ and $f_2$ on $X_2$; this makes sense by the hypothesis that $f_1 \rvert_{X_1 \cap X_2} = f_2 \rvert_{X_1 \cap X_2}$.
Comment: @RaymondCheng: that only works to define the map on topological spaces. You need to say what happens to the map of structure sheaves, so you need some relation between $\mathcal O_{X_1}$ and $\mathcal O_{X_2}$ on the one hand and $\mathcal O_{X_1 \cap X_2}$ on the other.
Answer: This is true in a suitable sense: if the closed subscheme $X_i$ is given by the ideal $\mathcal I_i$, then $X_1 \cap X_2$ is given by $\mathcal I_1 + \mathcal I_2$. In this case, it is true that
$$Y = X_1 \underset{X_1 \cap X_2}\amalg X_2,$$
where $Y \subseteq X$ is the closed subscheme given by $\mathcal I_1 \cap \mathcal I_2 \subseteq \mathcal O_X$. Your assumptions imply that $|Y| = |X|$, but the scheme structures may be different. However, everything is ok as long as $\mathcal I_1 \cap \mathcal I_2 = 0$. See for example [Sch05, Thm. 3.4, Thm. 3.5, Cor. 3.9].
Here is an example to show what can go wrong:
Example. Let $X = \operatorname{Spec} k[x,y]/(x^2y^2)$, and let $I_1 = (x)$ and $I_2 = (y)$. This is the naive thing to do, because $I_1$ and $I_2$ are the minimal primes of $X$. However, $I_1 \cap I_2 = (xy) \neq 0 \subseteq k[x,y]/(x^2y^2)$, showing that
$$X_1 \underset{X_1 \cap X_2}\amalg X_2 \cong \operatorname{Spec} k[x,y]/(xy).$$
The natural maps $X_1 \to X_1 \amalg_{X_1 \cap X_2} X_2 \leftarrow X_2$ agree on the point $X_1 \cap X_2 = \operatorname{Spec} k$, but they cannot come from a map $X \to X_1 \amalg_{X_1 \cap X_2} X_2$. Indeed, suppose $\phi \colon k[x,y]/(xy) \to k[x,y]/(x^2y^2)$ is a ring map whose compositions with $k[x,y]/(x^2y^2) \to k[x], k[y]$ are the projections. Then $\phi(x)$ is congruent to $x$ modulo $y$ and to $0$ modulo $x$. Therefore,
$$\phi(x)-x \in (x) \cap (y) = (xy) \subseteq k[x,y]/(x^2y^2),$$
and similarly for $\phi(y)-y$. If $\phi(x) = x + fxy$ and $\phi(y) = y + gxy$, we need
$$(x+fxy)(y+gxy) = 0 \in k[x,y]/(x^2y^2).$$
But the $xy$ term is visibly nonzero, so $\phi$ does not exist.

References.
[Sch05] Schwede, Karl, Gluing schemes and a scheme without closed points. In: Kachi, Yasuyuki (ed.) et al., Recent progress in arithmetic and algebraic geometry. Proceedings of the 31st annual Barrett lecture series conference, Knoxville, TN, USA, April 25--27, 2002. Providence, RI: American Mathematical Society (AMS) (ISBN 0-8218-3401-0/pbk). Contemporary Mathematics 386, 157-172 (2005). ZBL1216.14003. Online version.


What is a background check?

Question: I wanna understand the meaning of the background check? Like I don't know how to do one or even get one. I really want to know the purpose of a background check.
Comment: You can Google the term to understand what employers are looking for. They usually don't do the looking themselves, but farm it out to specialized services.
Comment: I googled for you.  Try this: https://techjury.net/blog/what-does-a-background-check-consist-of/
Answer: Boykah ... the purpose of the BACKGROUND CHECK, is for employers or other 'entities' to obtain an unbiased report on WHOM they are dealing with, in the person who is being 'checked out'.  The Background Check will include such things as Criminal Record, Credit Report, Education, Employment, and more.
Wikipedia explains it overall quite well:  The objective of background checks is to ensure the safety and security of the employees in the organization. These checks are often used by employers as a means of judging a job candidate's past mistakes, character, and fitness, and to identify potential hiring risks for safety and security reasons.
In decades past a person's reputation was a treasured element of their life and livelihood.  Today, because more people are lax in the care of their reputation; as well as a growing concept that one's reputation is more 'flexible'; employers and others dealing with an individual find it necessary to do their 'due diligence' (you may be interested in the background on this term as well) and make sure the individual will be a POSITIVE addition to their entity and NOT a negative problem to be avoided.
This leads to all sorts of complications, oversights, prejudices and negative social outflow, but it's become the 'lesser of two evils'.  Choose bad by being lax in the 'background check', or be seen as a bit more antiseptic and less personal, and NOT inherit an unwanted problem.
Comment: Your analysis is a well-written opinion. An authoritative answer here does not include my opinion, though, or *I hope*. And frankly, with the work done once you pointed to Wikipedia, the question itself needs no work on our part.
Comment: A referenced and well discussed view. I have removed the unnecessary epilogue.

What is a background check?


Definition of chain (Rudin)

Question: In "Real and complex analysis" a chain is defined as "a sort of formal sum of paths". Given a family $\lbrace\gamma_1,\ldots,\gamma_n\rbrace$ of paths, the chain $\Gamma$ corresponding to these paths is "a sort of formal sum $\Gamma=\gamma_1\dot+\cdots\dot+\,\gamma_n$" and the line integral of this is defined as follows:
$$
\int_\Gamma{f\,\mathrm{d}z}:=\int_{\gamma_1}{f\,\mathrm{d}z}\,+\cdots+\int_{\gamma_n}{f\,\mathrm{d}z}
$$
I don't like such pseudo definitions since they tell me what I can do with an object, but not what it actually is. So what is a chain really?
Thanks
Comment: It's an element of the free abelian group whose basis is the set of all paths.
Comment: @Chris: I am not convinced that it should be the free _abelian_ group as opposed to just the free monoid over the set of all paths. :-)
Comment: @WillieWong Don't we want to take orientation into account, which is where the inverse structure comes in?
Comment: @AlexYoucis: yes and no, depending on how we look at it; in any rate, I don't think it's good to see it as a *free* abelian group. I'm writing an answer to reflect on that right now.
Comment: @Alex: I was being partly facetious. But the phrase "a sort of formal sum..." does not necessarily suggest an orientation. For example, a very similar definition can be made about the [line integral](http://en.wikipedia.org/wiki/Line_integral) in the real case, where the integral is not direction dependent.
Answer: This is more in the abstract-algebra territory rather than complex-analysis (especially not the complex part; the definition of path integral does not really depend on complex structure), but I see two (or three) ways of properly formalizing that.
One way is to follow Willie Wong's suggestion, and take for chains the free monoid with a basis of (sufficiently well-behaved, for instance $C^1$) paths, that is, a $\Gamma$ is a chain if it is a finite sequence of paths, and we add chains by appending one at the end of another; for the remainder of this post, call this monoid $Ch_1$
Another, closely related, is to take it to be instead the free commutative monoid defined by the nice paths -- this is the same as above, except we forget the ordering of the sequence. This is the most literal reading of the statement "formal sum" -- a formal sum of things is, to me anyway, the commutative monoid generated by them. If we call it $Ch_2$ we can see that this is just $Ch_1$ divided by the relation $\Gamma_1\Gamma_2=\Gamma_2\Gamma_1$.

A third, quite a bit more complicated way to interpret it is to take into account what we actually do with the chains: we integrate along them. Furthermore, if we restrict ourselves to nice functions (for instance, globally continuous), we can see that for two very different chains $\Gamma,\Gamma'$ we have $\int_\Gamma$ being the same thing as $\int_{\Gamma'}$ (as linear functionals on the space of continuous functions), for example if $\Gamma'$ is just a subdivision of $\Gamma$.
One way to formalize it is to just equate a chain $\Gamma$ with the integration operator $\int_\Gamma$, effectively seeing the chains just a subgroup $Ch_3$ of the additive group of the dual of the space of continuous functions, $C({\bf R}^n)^*$ (or $C({\bf C}^n)^*$). This means that in particular, we see that the chain consisting of a path $\gamma$ and the path $-\gamma$ obtained by reversing the orientation on $\gamma$ is equated to an empty path – that is because for a continuous function $f$ we have that $\int_\gamma f+\int_{-\gamma} f=0$.
While the reference to the dual of continuous functions may seem rather technical, this is, I believe, the intuitive way to see chains. I think that's where the convention to write $-\gamma$ for an inverted path comes from in the first place.
There is a minor gripe for it: if we integrate functions that are not globally continuous, for example ones that have singularities, such as $z^{-1}$ on ${\bf C}$, we will have pairs of chains that are equivalent, but such that we can integrate along one, but not the other, for example if we take $\gamma$ to be the interval from $-1$ to $1$ on the complex plane, then the equation $\int_\gamma z^{-1}+\int_{-\gamma} z^{-1}=0$ doesn't make sense. This wasn't a problem at all in case of $Ch_1,Ch_2$, since in those ones we never really cancelled any terms.
But it's not that much of a problem in this case, as equivalent chains for which the integral is well defined will integrate a continuous function consistently, even if it is not globally defined.

Definition of chain (Rudin)


Do we need use case levels or not?

Question: I guess no one would argue for decomposing use cases, that is just wrong. However sometimes it is necessary to specify use cases, which are on lower, more technical level, like for example authetication and authorization, which give the actor value, but are further from his business needs. Cockburn argues for levels when needed and explains how to move use cases from/to different levels and how to determine the right level. On the other hand, e.g. Bittner argues against use case levels, although he uses subflows, requires the vision documents which contain information about the purpose of the system in the business, much like use cases on the higher level, and at the end of his book mentions, that at least two levels are needed most of the time.
My questionis, do you find use case levels necessary, helpful or unwanted? What are the reasons? Am I misssing some important arguments?
Answer: I recommend against levels.  The use cases are most useful when they describe what the user wants to accomplish, not the technical details of how to they do things.  Making the use cases specific to methods will constrain your choices on how to implement solutions.  In your example, the use case should be "check the balance of his account", not "the user can log on with SSL".
That said, make the exception when your requirements contract does have highly specific technical constraints.  If your client demands SSL, make the SSL use case.
Comment: I know technical details, UI, business rules, law etc. are details abstracted from in use cases. For example imagine set of use cases for a system requiring authetication and authorization. You may start with "...his...", but than you will need preconditions which will be repeated everywhere, so you do include and voila, new use case, which is important to the actor, but less than others, e.g. it is on the lower level.
Comment: I consider authentication and authorisation to be the sort of technical details that are normally not interesting to build use cases.  Authentication and authorisation are not things the user wants to do, but a technical detail in the way of the user's final goal.
Comment: e.g. with ATMs people want to perform transaction on their accounts and they want to prevent anyone else from doing that, the technical details on how you do it are unimportant, but the fact that user needs and authentication and authorisation is imho obvious.
Comment: When a person uses an ATM, the uses cases would be to withdraw money, cash a cheque, check an account balance &c, the security is a technical detail of how to achieve the aforementioned goals.  That's not to say security is unimportant to the user, but it is not what the user wants to get done.

Do we need use case levels or not?


libusb couldn't open USB device /dev/bus/usb/002/006: Permission denied. libusb requires write access to USB device nodes

Question: I am connecting my FTDI Device with Laptop USB. I was following all the steps given in the link How to build libftdi git under Linux
But after installing.. When I was running ./eeprom it is throwing:
Unable to open device -1: (libusb_open() failed)ftdi_read_eeprom: -2 (USB device unavailable)

I installed FTDI D2XX driver from link:
D2XX for Linux
After installing, I was trying some examples to write in USB EEPROM.
$sudo ./write

It is throwing:
libusb couldn't open USB device /dev/bus/usb/002/006: Permission denied.
libusb requires write access to USB device nodes

I was setting
cat /etc/udev/rules.d/85-ftdi.rules
SYSFS{idVendor}=="0403", SYSFS{idProduct}=="6001", MODE="660", GROUP="ftdi-user"

Then also, it is not working. Same error is coming.
Answer: SYSFS was deprecated in favor of ATTR/ATTRS. See hotplug/udev.git
Try with:
ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", MODE="660", GROUP="ftdi-user"


In what way can Google deepdream be extended? Is there an image dataset which can use hallucinations produced? Any deepdream useful application?

Question: Is there a particular section of image data which when trained on deepdream algorithm and given some input image produce a resulting image from which we can conclude that the deepdream can be used for this image set (other than just producing hallucinations on input image for fun) ?
Comment: I can't actually understand what you're asking. I think it would be helpful if you broke your question down into more than one sentence.
Comment: As @DavidRicherby suggested, it would be helpful to clear things a bit, but by editing the question, not the comment. Also I am afraid that your question can be downgraded to "I have the image filter X, can I do anything reasonable (or just different then intended art effect) with it?", which is not clear objective.
Comment: You ask three different questions in the title alone, and I can only second David's concerns. Please tighten up your post to ask *one* clear question. (You may have to do some research in order to do so.)
Comment: According to my understanding deepdream algorithm is trained on a set of images (say suppose dogs) and when we give the input image of sky, it detects the features of image that are similar to dogs and amplifies it. I wanted to know if there is any image set that when we train on deepdream produces results that can be used for any other application. Or is there any other useful application of deepdream ? I am not sure if my understanding is right, so kindly corrct me if i'm wrong
Comment: By not clear objective I mean that there might be a dozen of applications - and there is no way of telling which one is better, a.k.a opinion based...
Answer: Google deepdream can be extended and has been extended in many ways as below:

Image segmentation (link)
Beautifying pictures/photos and human faces and bodies
Image upscaling
Greyscale to Color
Censoring and go on..

Here, somebody using MIT's places data to train the deepdream (video)
Most of the problems in the list are at amateur stage still its one step to perfection.
If interested, you should play/improve/contribute with the code here GitHub


What is the most efficient way to convert a fuel into electrical energy?

Question: Large steam engines seem to get pretty good efficiency, but there are other options such as combustion turbines.
Ignoring all other considerations, what methodology can extract the most energy out of a given amount of fuel?
Comment: Is there an underlying problem that you are trying to solve here?
Comment: Depends a lot on your definition of "fuel."  Mass - to - energy via annihilation will give you a buttload of energy to start even if you settle for the low -efficiency of the Carnot cycle after that :-)
Comment: @CarlWitthoft that also depends a lot on your definition of "efficiency". Such processes are typically about 2% efficient in terms of potential energy -> electricity.
Comment: > Is there an underlying problem that you are trying to solve here? – EnergyNumbers 2 days ago

Not as such. I admit it is a little open-ended. Mostly I'm looking for general information about what types of technology perform well in this class.
Answer: In theory, direct chemical to electrical energy offers the highest efficiency: it can deliver arbitrarily close to 100% efficiency. However, to date, fuel cells haven't delivered on anything close to that promise.
In theory, the worst way to do it, in efficiency terms, is to go via heat - e.g. by burning the fuel. That throws away a lot of the exergy (the ability of the fuel to do work) straight away. The amount that's irretrievably thrown away is given by Carnot's Law, and is determined by the absolute temperatures of the combusting fuel, and of the sink where the cooling happens.
The hotter the combustion, and the colder the sink, the more efficient the process can be.
The best-in-class combined-cycle gas turbines (CCGT) deliver around 60% efficiency, by combining a steam turbine with a gas turbine. And to date, that's about as good as it gets for fuel consumption.
Answer: We need to go directly from chemical energy to electrical energy.  Electrical energy can be attained by accelerating electrically charged particles through a coil or magnetic field, which causes electromotive force (voltage) and electrical current through a load to do work to neutralize the voltage.
The chemical reaction of fuel with oxygen is known as oxidation reduction and is exothermic.  That means that the end products of the reaction are more stable in terms of the resulting molecule's outermost electron sub-orbitals and pairing of electron spin defined by Pauli's exclusion principle and quantum mechanics.
Since the end product is more stable, energy is released (exothermic).  This energy is manifested as photon emission as the electrons settle into the lower energy level orbitals, and as increase of the average kinetic energy of the molecules (heat) in this exhaust.
According to Boyle's law, the increased temperature of the exhaust gas causes expansion of said gas to fill a greater volume (less dense).  This thermal expansion of the exhaust gas is what drives the turbines in a gas turbine electric power generation setup, jet engine, rocket engine, and what pushes the pistons inside the cylinders in an internal combustion engine.
Now, the trick to converting directly to electrical energy is to ionize the molecules of the exhaust gas at the point of combustion and keep these molecules ionized as they accelerate through a magnetic field producing electrical energy.
The efficiency of this setup would be determined by how much of the exhaust gas can be ionized and how much of the thermal energy of this ionized exhaust could be extracted.  As the charged gas goes through the magnetic field it would slow down (cool) and/or possibly lose charge.  The greater the temperature difference between the point of combustion and the end of the magnetic field pipe, the greater the efficiency.
We are converting the thermal kinetic energy of the ions directly to electrical energy.
Or, we can extend (stretch) the entire flame, or ionized process of combustion through the entire insulated tube which would be surrounded by magnetic field.
A straight linear tube would avoid x-ray photon emission caused by rotational acceleration if the tube were curved, but this x-ray emission could be useful in keeping the gas ionized.  So a circular or spiraling setup may also work.
Also, a pulsed gas setup may work better than a continual stream.  The frequency of pulsation could be fine tuned to the physics of the system for optimal efficiency.
Answer: Scale matters as does the type of fuel. Steam power, in general, has the advantage that the boiler is physically separate from the working fluid and from the working parts of the engine itself and you can design the combustion and heat exchange process independently from the engine. So steam power lends itself well to using solid fuels which burn relatively slowly and leave a solid ash residue such as wood, coal and waste biomass and of course nuclear reactors.
Also steam power, using water as a working fluid with phase change means that there are lots of opportunities to recover waste heat as the working fluid is recirculated rather than being dumped to the atmosphere.
Gas turbines are typically a bit less efficient but more flexible as they can achieve peak efficiency at smaller scales so in a grid system steam turbines may be used for the ongoing base load and gas turbines to pick up peak loads.
Obviously gas turbines also require specific types of fuel.
Of course in the real world pure thermal efficiency matters less than economical considerations of fuel cost and availability, capital cost of plant and legislative constraints such as subsidies and penalties.


Why does Google Chrome require you to have admin access to be set as the default browser?

Question: Neither Firefox nor Internet Explorer requires admin to set as default. Why does Chrome require it?
Comment: What basis are you making this under?  That was not my experience, and I have reinstalled it numerous times over the few years I have used it.
Comment: The simple answer is that Chrome installs in such a way where the profile is NOT connected to the user.  Firefox actually requires proper permissions to be installed as a normal User, because the Firefox profile, is connected to the User profile itself.  What is the purpose of this question?  **If you are trying to block this behavior there are better ways to prevent it.**
Answer: There are multiple ways to associate file-types and protocols with a program. For something complex like a web-browser which can support several file-types and several protocols, there are numerous settings that have to assigned to make it the default browser. Worse, there are numerous other hooks into the system that a browser can set these days such as making a buttons in the Start menu, shortcuts in the taskbar, integrating with the shell and email clients, and so on.
So there are quite a lot of different settings to be modified, mostly in the registry, a few in the file-system. Some are mandatory (e.g., http protocol, .url shortcuts, .html files, etc.), but others are optional. As a result, some browsers will set some which others don't (few, if any, configure set every single possible setting).
Some of these numerous settings are in user-accessible places while others are in areas that require higher privileges.
In addition, Windows essentially duplicates a lot of things on a system-level and a user-level. For example, you can set some things to apply to individual users or to the whole system (or both). Not surprisingly, changing a system-level setting will require administrator permissions.
Obviously Chrome configures some settings that require extra privileges and/or modifies both the user and system versions of some settings.
Comment: If you want to know *specifically* which privileged values it sets, then you can use [Process Monitor](http://technet.microsoft.com/en-us/sysinternals/bb896645.aspx) to observe what file and registry changes it makes when you click the *Make default* button.


Any way to get VMware Fusion's Shared Folders working with 11.04/Natty guest?

Question: Just upgraded to Natty this morning. I know, I should have waited until VMware updated Fusion for it, but I was impatient. :-) I can't seem to get Shared Folders working now... anybody have this working, and if so, what's the trick?
Answer: Just managed it.
Some of the VMware Tools modules supplied with VMware Fusion 3.1.2 seem to have problems compiling under 11.04. I'm a programmer, but rather than trying to fix them (which could become a huge time-sink), I thought I'd try the open-vm-tools package, since that's available for 11.04 and should be essentially a precompiled version of the same thing.
It didn't work at first, but I found this page describing the proper way to install them -- you apparently have to install open-vm-dkms first (not sure why, I'd think it would auto-install as a dependency, but it didn't). After that, install open-vm-tools. Then in the VMware Fusion settings, turn OFF Shared Folders, then turn them back on.
After that, my shared folders appeared in /mnt/hgfs as normal. :-)
Answer: Read this blog for solutions to VMware Tools compilation errors under Ubuntu 11.04 and VMware Fusion 3.1.2
Comment: Whilst this may theoretically answer the question, [it would be preferable](http://meta.stackexchange.com/q/8259) to include the essential parts of the answer here, and provide the link for reference.


Electric Stove burner wattage matter?

Question: Is it ok to put a higher wattage burner element on your stove than what stove calls for? I bought the wrong burner wattage but it does fit etc.
Comment: This question appears to be off-topic because it is about *repair* of a cooking appliance, not design features, selection, or other *culinary* aspects of the appliance.
Comment: The tag wiki says "Questions on selecting, **maintaining**, and using cooking tools and equipment." Are we going back on that? (Or do we need to clarify the difference between "maintain" and "repair"?)
Comment: There is a chance it'll work out.  But It's a **bad idea** all around.  You can blow the fuse in the stove among other things.  If the stove isn't designed to dissipate the wattage, you'll blow the element, too and end up back where you started.
Comment: I agree that this is off-topic. I suggest going to [diy.se] and browsing their questions to see if this will fit there.
Comment: @Jefromi This is well past maintain.  Maintain would be cleaning the oven, or removing the burners to clean under them, then reseating. Its the same as the difference between sanitizing a cutting board (definitely culinary), sanding one down (borderline), and building one (definitely not culinary).  Repair is not a culinary skill unless the item breaks so often in my mind that the repairs are routine.
Answer: Apart from blowing a fuse your problems may be worse than that. Most electrical appliances are designed with the assumption that all the components used are within specification. One example failure mode I can think of is that your new heating element may heat the attached wiring to unacceptable levels and increase its electrical resistance due to both the extra current flowing and the increase in ambient temperature.
Increased power loss though the wires will won't cause a fuse to trip but may cause a fire. I'd recommend replacing the element with one that has a rating similar to the original. In addition to safety aspects your temperature controller (often called a simmerstat) may not be rated for the additional current required and may fail prematurely.

Electric Stove burner wattage matter?


PHP form validation - adding a validation tick box

Question: I'm using this tutorial to try and make a form http://www.javascript-coder.com/html-form/javascript-form-validation.phtml
My form works great but I have included 3 tick boxes that I want the user to tick before they can submit. Creating this validation has had me scratching my head all day!
I've tried making these custom fields but am pretty sure my syntax is wrong. I am well out of my depth here! The tutorial provides example that I tried to implement but the coding is too different for me to use on my form. This is what I tried:
<input type="checkbox" name="checkbox1" id="checkbox1" />
<label for="checkbox" value='<?php echo $formproc->SafeDisplay('email') ?>'

And then after the form, inside the script adding:
frmvalidator.addValidation("checkbox1","checkbox1","Please tick the box before pressing submit");

The form still submits but my validation doesn't happen. If anyone can point me in the right direction, that would be really incredible.
I'm not sure if it's the done thing to post the actual page I'm working on as it's my clients website?
Comment: It would be really worth your time ditching the slightly confusing syntax of that black-box validation tool and learning how to do it in raw Javascript. It's really not too hard, and it will be a *lot* more flexible.
Answer: It's in the documentation.
frmvalidator.addValidation("checkbox1","shouldselchk=on");

Answer: First you need to give value to your checkbox as below
<input type="checkbox" name="checkbox1" id="checkbox1" value="1"/>

Then, you need to pass type of validation in second argument of addValidation function as below
frmvalidator.addValidation("checkbox1","shouldselchk=1");


Does having a gimball mean you can disbale stability on action camera

Question: It's common for action cameras to have a lower frame rate when the electronic stability function is turned on.
My question is if you have a gimbal, is it useful/do you need to have electronic stability enabled on the camera itself?
Answer: As Michael Clark pointed out when the question was on photography, it depends on the type of gimbal, how good the gimbal is and how skilled the operator is.
An inertial gimbal works by giving the camera assembly a larger size and mass and then having the operator hold the assembly near the center of gravity.  When the operator moves, inertia slows changes in the orientation of the camera, resulting in smoothing of angular changes.  This requires the gimbal to be very near frictionless to minimize the impact of the operator's movement on the rotational inertia of the camera assembly.  A low quality or poorly maintained gimbal won't properly isolate the assembly and an unskilled operator may improperly balance the assembly or cause excessive motion do to the added weight and complexity of operation.
A robotic or motorized gimbal, such as a Ronan, acts on a slightly different principle.  They do not require the finesse of the operator to execute changes in camera direction as this is accomplished by a joystick (less direct control, but easier to operate).  Additionally, they are not quite as balance sensitive as the orientation correction is provided by gyroscopes and motors which can tell what's actually happening vs a simple passive physics based system.  Additionally, counterweights aren't needed for stabilization so the rig can potentially be lighter overall making it easier to handle.  The down side is the previously mentioned lack of direct control and the power requirements.  Additionally, the quality of the gimbal still becomes a major factor.  If gyroscopes are not sensitive enough or the motors are too imprecise or laggy, then the quality of the stabilization will be greatly reduced.
Both of these types of gimbals are designed for correcting 3 degrees of orientation and do not handle any lateral movement on their own (adding things like vest & arm systems can add some position stabilization as well, but weren't specifically mentioned in your question.)
Image stabilization on the camera depends on the camera.  Some use movement of lens elements (optical image stabilization) to correct the direction the lens is pointed as the orientation changes.  Others use free floating sensors that are able to move in response to motion to keep the sensor in the correct orientation and location in the image circle.
The amount of correction that either of these in-camera systems can provide is extremely limited since they don't govern the actual aiming of the camera body, but they can help with a degree of hand shake.  There is one noteworthy distinction though.  For the floating sensor types of camera stabilization, it is possible to correct of a limited degree of positional stabilization, not just orientation as the sensor can move up and down and side to side a bit.
In general, I would expect that with a half way decent gimbal and even intermediate experience as an operator, you should get much better overall results with the gimbal, but depending on your shooting situation, you may still gain some additional benefit from the camera's built in stabilization if it has a floating sensor particularly.  You really need to try messing with it either way though as the movement may be sufficient to throw off the balance and cause issues with the gimbal as well.
Certainly the effects should be pretty minimal, so if your primary concern is recovering the higher frame rate, then using a gimbal and turning off the in camera stabilization won't give you a major sacrifice in stabilization quality.
Answer: Any type of stabilization requires trade-offs, IMHO. Motorized/Gyro mounts are not cheap, and are bigger and weightier than most action camera scenarios I can imagine using, especially when you get 4 and 5 axis controls. Most action cams seem to have a very short focal length lens so the apparent motion is minimized while the field of view is increased. I think this is a design criterion for them.
In my experience with my action cam (a Garmin VIRB Elite) I found that the built-in stabilization kinda-sorta works. (I have not used a newer Garmin or a GoPro, they may do better.) The stabilized image seems to suffer from block artifacts in the biking videos I have shot, using the stabilization. I finally got a helmet mount instead of the handlebar mount for the VIRB, and use the camera without internal stabilization. This gives me acceptable frame rates with the action camera, all by using my head.
For just walking around and fairly stable shooting, I have my handlebar mount attached to the top of a weighted walking stick. Keeping a firm but soft grip on the stick gives me a very good poor-man's steady mount for the action cam. You can do the same sort of thing with a heavy (i.e. professional) tripod and your "other" camera. (Light-wight computer store or big box store tripods don't have the mass to do this, again IMHO.) Just be sure not to run the bottom of your steady mount into the ground, that really spoils shots.
One last caveat. Read the Fine Manual. There are often specific situations the documentation of good cameras will recommend that certain digital features be turned off. They don't tell you to do things like that if it were not important to help get you good pictures and videos.


MFC resources Vista vs Win7 compatibility

Question: Original app was developed with VS6 MFC for WinXP - then ported to VS 2005 Vista, and runs fine in Vista.  However, when installed in Win7 the app runs without crashing but the UI is scrambled.  Windows controls all seem to line up on left edge of main window.
Can this app created with VS2005 in Vista run properly in Win7?  Or does it need to be compiled and linked in Win7 to run properly in Win7?
Answer: The most likely explanation is that your program has bugs in it, or rather it makes assumptions about Windows that aren't valid: a correctly written program built on an old system with an old version of Visual Studio will work fine on Windows 7. As ever, just because something worked on old versions of Windows doesn't prove it's "right".
There aren't any easy shortcuts for this: you're going to have to debug your application to figure out what is wrong with it.


Can I placed a firewall between a core switch and router running on trunk mode?

Question: Router port facing to Core switch is running trunk mode  allowed vlan 200 & 300.
I am placing a firewall between the trunk connection.
Can I set the firewall as L2 transparent mode or I need to configure the firewall as trunk mode for both ports?
The setup i was wondering whether firewall normal switchport interface can it talk to the router port trunk mode? It is like connecting a PC/L2 switch to the router trunk port. I was wondering whether it works and concept behind.
Thanks guys! I need help!
Comment: What kind of firewall? (Manufacturer, OS?)
Comment: Is it a non-famous brand. Howveer the same concept shld applies for all firewall. The question is does the firewall need to set as transparent or trunk mode in order for traffic to pass through from core sw to router without any interruption
Answer: A firewall can be L2 transparent (depending on configuration), but that's not quite enough.
For full functionality, the firewall needs to recognize VLAN tagged frames and look inside them for IP. It's possible that some types might do this automatically. But others might require a separate virtual "VLAN interface" to be configured on the firewall for each and every VLAN ID.
If the firewall is merely L2 transparent but doesn't understand VLANs, then it won't protect them: either it'll drop the frames as unknown, or bypass them as unknown.


how to accessing gpio from another computer web server

Question: i'm doing a project for face recognition with raspberry pi. but i want my web server is from my laptop and my raspberry pi just accessing the web app. the point is, all of stuff is done in my laptop web server. but i don't know how to send signal to raspberry gpio from another computer web server to raspberry pi ? does anyone has a solution ? pardon my english. Thanks !
Answer: If you use the pigpio library and run it as a daemon on the pi, you can run local Python code that access the GPIO port on the remote pi.
If you are new to this, you might also want to check out the gpiozero project.


Adding to a ASP.NET user control constructor

Question: I've created an asp.net user control and I am trying to add logic to the user control's constructor. When I added the constructor to the user control I received an error telling me there were duplicate constructors. I'm assuming asp.net is creating one for me and then creating mine separately. How do I add logic to my User control constructor?
Answer: Try overloading the constructor....


How are DNA polymerase error rates measured?

Question: It is well known that the first DNA polymerase, Taq, is quite error prone. Newer generation commercial enzymes that have either been isolated from different thermophile species or have been improved by recombination are less error prone. How are these error rates compared? For instance, if this is done by Sanger sequencing, the average signal will dominate in reading the output and so it will be very unlikely to pick up on errors by this method.
Comment: The Taq products could be cloned before sequencing. It's still complicated though, because the same error in two products could represent the same error arising de novo twice, or the propagation of a single error that arose in an early round of amplification.
Comment: This is why I was sceptical about a sequencing-based approach. I suppose the method described by Alan Boyd below is a functional approach, but this still masks synonymous mutations and therefore under-represents the true error rate.
Answer: According to their website New England Biolabs use a version of the approach pioneered by Wayne Barnes, as described in:

Kermekchiev, M.B., Tzekov, A and Barnes, W.M. (2003) Nucl. Acids Res. 31, 6139–6147

This is basically an assay for the mutation rate in a PCR-amplified lacZ (β-galactosidase) gene, assayed by transforming E. coli, plating on the chromogenic β-galactosidase substrate Xgal, and then scoring white colonies as mutated genes. Also according to NEB, Agilent Technologies use a similar mutational assay, but based upon the lacI (lac repressor) gene.
Comment: Thank you for the reference. This seems like the most pragmatic approach to this problem. Even though by design this method under-reports the error rate, it would be a consistent bias across polymerases.
Comment: It's possible that they have calibrated the mutational assay to a more rigorous approach somewhere along the line, but I'm just guessing. As you say, for them the relative fidelity is more important than the absolute value.


How do I use 2 drives on linux on virtualbox?

Question: I failed to increase the actual size of that disk with 30G so I created another drive but I don't know how to access it. How can I access this other hard disk with 100.7G so that the other doesn't complain of space no more.
Answer: In your current setup the only way is to create filesystem and mount it somewhere and use it.
mkfs -t <your preferred filesystem> /dev/sdb1
mount /dev/sdb1 /some/mountpoint

(the above commands must be executed as root or via sudo)
If you had LVM then you can just add this disk to the VG and extend and/or add LV/filesystems
Answer: This does not exactly answer your question "How do I use 2 drives on linux on virtualbox?", but may answer the root problem.
The running OS , looks like Ubuntu, and running programs may not use the newly mounted hard drive for space it needs. Locations like /tmp and /home/user are some of the locations used by linux and the Gnome desktop.
If the new drive is mounted at /mnt/more_space that will not prevent the OS from complaining that it is running out of space.
Fixes include:
You could move some files from the small drive to the larger to free up space on the smaller drive.
You could change the location of your home directory or the tmp directory to the larger drive.
OR
You could increase the size of the smaller drive if it is in VDI or VHD format and dynamically allocated with the cli command VBoxManage modifyhd --resize 100GB.
NOTE: VDI and dynamically allocated are the defaults.
Then resize the partition to fill the new disk space.
OR
If your small drive is not VDI or VHD format and dynamically allocated...
You could create a new virtual drive. Attach it to the VM. (looks as if you have already done this) Clone the smaller drive to the larger drive with a program like Clonezilla.

Attach a bootable DVD to the VM like a older version of Parted Magic. I like it because it has all the tools needed in one place like partition editor and Clonezilla.
Set up new larger HD similar to the older small one. Example the first partition as ext3. Extended partition with a linux swap partition, generally the size of installed RAM. Tool used: Partition editor.
Create an image of the smaller drive. I recommend device-image vs. device-device in Clonezilla. You will need a third place to put the image. It will be compressed so should be much smaller than the 26GB size of the drive. Tool used: Clonezilla. (device-image) (location of place to put image) (Beginner) (saveparts) (...)
Restore the image to the larger drive. Tool used: Clonezilla.
Fix new drive UUIDs in etc/fstab/. Tools used: blkid to get new drive UUIDs. Text editor for fstab. vi /etc/fstab.
NOTE: You can do these changes in Parted Magic before you reboot.


If God created us with the capacity of free will. I choose to leave this life and be up there and watch the world beside him, why is it not happening?

Question: If God created us with the capacity to love and thereby giving us the ability of free will, the ability too choose. He has given us the choise to be a decent human beings but also the choise to commit sin, which he does not like and that is understandabe but he allows it. With my ability to choose why can I not choose to leave this place, my body, this life, and simply sit beside him and watch the world with him?
Comment: Not having the ability to realise any choice you can imagine (like having the ability to fly) doesn't mean the choices you can make aren't real.
Comment: So God allows us to behave the way we want, the actions we commit are real but he does not allow us to realise any choise we have. It's like we have free will but at the same time we do not. God put the rule that you can only leave this place if you are dead. If you are dead God decided that you are unconcious and that you are too await resurrection.
Comment: @MauricioRamirezZavala God is God. He makes the rules for our benefit. Your life is important and there is a big mission for you to fulfill, but you decide whether you take the mission, or do what you want in this life. This life is borrowed. You did not work to create your life, God lent it to you. If you do nothing with it and waste it, as many do, you will be judged according to your work. See the parable of the talents.
Comment: @MauricioRamirezZavala I'm afraid your cavalier attitude toward life and free will is **not** how God our creator intended us to use, just like a parent giving freedom to a teenager.  God loves you and wants you to flourish.  Free will is a gift with responsibility attached.  Free will properly exercised will elevate you to amazing communion with God, not intended to do nothing.  Also remember God is King.  Do you think you can just sit next to Queen Elizabeth without invitation and worthiness?
Answer: This is from an SDA perspective.
That depends on what your belief is of what happens after death. Based on the Bible, when you die, you are unconcious and await the resurrection.
There is Biblical support that supports the idea of death sleep:
The dead do not know anything:

For the living know that they will die; But the dead know nothing, And
  they have no more reward, For the memory of them is forgotten.
Ecclesiastes 9:5

The dead cannot do anything:

Whatever your hand finds to do, do it with all your might; for there
  is no activity or planning or knowledge or wisdom in Sheol where you
  are going.
Ecclesiastes 9:10

The dead cannot praise God, or hope in His faithfulness:

For the dead cannot praise you; they cannot raise their voices in
  praise. Those who go down to the grave can no longer hope in your
  faithfulness.
Isaiah 38:18

There is no mention of God by the dead:

For there is no mention of You in death; In Sheol who will give You
  thanks?
Psalms 6:5

Jesus mentions that Lazarus, who was at the time dead, was simply sleeping:

11 These things He said, and after that He said to them, "Our friend
  Lazarus sleeps, but I go that I may wake him up."
12 Then His disciples said, "Lord, if he sleeps he will get well." 13
  However, Jesus spoke of his death, but they thought that He was
  speaking about taking rest in sleep.
14 Then Jesus said to them plainly, "Lazarus is dead. 15 And I am glad
  for your sakes that I was not there, that you may believe.
  Nevertheless let us go to him."
John 11:11-15

Paul says that those who sleep, or died in Christ, simply wait for His return and their resurrection.

13 But I do not want you to be ignorant, brethren, concerning those
  who have fallen asleep, lest you sorrow as others who have no hope. 14
  For if we believe that Jesus died and rose again, even so God will
  bring with Him those who sleep in Jesus.[b]
15 For this we say to you by the word of the Lord, that we who are
  alive and remain until the coming of the Lord will by no means precede
  those who are asleep. 16 For the Lord Himself will descend from heaven
  with a shout, with the voice of an archangel, and with the trumpet of
  God. And the dead in Christ will rise first. 17 Then we who are alive
  and remain shall be caught up together with them in the clouds to meet
  the Lord in the air. And thus we shall always be with the Lord. 18
  Therefore comfort one another with these words.
1 Thessalonians 4:13-18

From this perspective, you don't watch the world, as mainstream Christianity would have you believe. It is unbiblical and was adopted from Greek Philosophy.
Comment: While many take exception to the doctrine of soul sleep, myself included, I appreciate the depth of this answer, particularly that it refutes the ideas in the question *without* addressing the nature of freewill, and much of your reasoning can be adapted without affirming soul sleep.


Work to time ratio!

Question: Once Valera left the house, walked to the villa, painted 11 fence boards there, and returned home
2 hours after leaving. Another day, Valera went to the villa with Olga, together they painted 8
fence boards (without helping or interfering with each other), left together and returned home
3 hours after leaving it. How many boards can Olga paint alone if she needs to return home an
hour and a half after leaving? The physical abilities of Valera and Olga, their hard work, and
working conditions are unchanged
Answer:
 The only way to make sense of the numbers is to assume that Olga moves much slower than Valera. Let us write tV and tO for the time Valera or Olga needs to get to the villa and back. And let us write vV and vO for their work rates, fence boards per hour. We then get two formulas:
  (1) (2h - tV) x vV = 11
  (2) (3h - max(tO, tV) ) x (vO + vV) = 8

 Because the unknown times and rates are nonnegative this yields inequalities:
  (1') 2h x vV >= 11
  (2') (3h - tO) x vV <= 8

 It follows:
  (3h - tO)/2h <= 8/11
  tO >= 2h x (3/2 - 8/11) = 17/11 h > 3/2 h

The answer is therefore

 0. Olga is too slow to get there and back in the allotted time, hence she cannot get any work done.
Comment: Sorry I did not understand your solution.

What is $3h - t_O$ ? What is $T_0$ ? How did you conclude that $0$ is the answer? Why $2h \times V_v >= 11$ ?
Comment: @MathR as it says in the answer t_O is the time Olga needs to get to travel to the villa and back. Since Olga is the slower of the two it is also the time Olga and Valera need when they travel together. 3h-t_O is the time they have left for working. The inequalities are obtained from the equations by leaving out terms we know are nonnegative.
Comment: 2 x (3/2 - 8/11) = 2 x (33/22 - 16/22) = 2 x (17/22) = 17/11

Work to time ratio!


Why are edits not presented to posters for review before they are approved

Question: It is frustrating to get a notice that your question has been reviewed and some questionable substitution approved, and you were not even aware that your question was even being considered for editing.
Answer: It's a reasonable question, but it comes from a misunderstanding.
Practically, yes, it is your post. You wrote it, your name is on it, and you get credit for it.
Theoretically, it is not really your post. It's not even SE's post. It is the community's post. It belongs to all of us equally and we all have equal right to submit peer reviewed edits. Here's why this theory of editing can work:

All edits are easily seen and can be rolled back if necessary.
Edits bump the post to the top of the active page, where pretty much every frequent user will see it. I personally check this regularly to make sure they are valid edits, and they almost always are.
Edits from low rep users are sent to the review queue where two high rep users must approve it before it is made public. Then it is bumped too.
The user who most recently edited is put at the bottom of the post right there with you, so there are no secret edits that someone should confuse with you having written.
You can always roll it back.

So there is really little reason to worry that the post will be invalidly edited without you or someone else noticing.
However, you might just want to know when this is happening. I personally think that is reasonable, but I bet SE will not make that adjustment to the notification system. You can try, however, to see it they will, by posting a feature request on Meta Stack Exchange. I searched and could not find this already existing, which surprised me.
Comment: @Bye In addition to what fredsbend has already answered, I would recommend you read [this section of the help](http://christianity.stackexchange.com/help/editing), which covers why people can edit your posts, and how it all works.
Comment: just to make the licensing super clear, it's owned by the poster, but licensed in perpetuity to Stack Exchange under a non-revocable CC-by-SA license. See http://creativecommons.org/licenses/by-sa/3.0/ for more info.
Comment: @Fredsbend I have not had a rollback option  on any of the proposed edits to Christianity stack exchange posts, was given one for the edit to this post.
Comment: @Bye Rollback is an option that you can click after going in to the edit history which is enterable on the active link that describes the last edit.
Comment: @Bye See [Caleb's answer](http://meta.christianity.stackexchange.com/a/3784/3961) for how to rollback. He made snapshots.
Comment: @fredsbend I checked out Caleb's post shortly after he posted it. unfortunately my text to speech software is woefully inadequate for the snapshots, but hopefully with what I did elicit along with some personal research I will eventually understand the procedures. While I have a lot of reps I am relatively new to the site, being legally blind I miss a lot of the little things about the site that are quite obvious to sighted users. It takes me little longer to learn things, but in time I will get there. So please do not give up on me, I'm not stupid (even though it may appear that way).
Comment: @fredsbend Please do not perceive any animosity in my last comment, after rereading it I sensed that you could feel that I was abrading you, and nothing could have been further from my mind. Please accept my apologies for any misunderstanding arising from my comment.
Comment: @Bye No apology necessary. I did not know you were so poorly sighted. I will keep that in mind. Textual descriptions will help you the best.
Comment: @Bye I added textual descriptions of the snapshots to [Caleb's answer.](http://meta.christianity.stackexchange.com/a/3784/3961)
Comment: @fredsbend Thanks I was not able get the part about the blue background. maybe now I can at least handle that problem.
Answer: In addition to the points noted by fredsbend I'll add a couple of notes on how the system is implemented:

There are two kinds of edits: suggested edits and edits.

Suggested edits can be done by anybody (even anonymous non-users), but they have to be approved by at least 2 high-rep members of the community. Anybody below 2k rep can only make these kind of edits. The changes do not appear immediately.
Once someone reaches 2k rep it is assumed that they have been around long enough to know generally how the system works and they are trusted to both make immediate edits.

In both cases, as the original author you are notified.

In the case of suggested edits you are notified that an edit has been suggested and, as the author of the post, you can approve or reject the edit unilaterally. If you don't catch this before other reviewers do, it takes 2 voters from the rest of the community to approve an edit.
In the case of normal edits, you are notified that one of your posts has been changed. The revision history is available to show exactly what they changed.

In both cases, edits are subject to review.
fredsbend covered this, but it bears repeating: all edits bump posts back to the home  page for community  review.
All edits can be rolled back. Whether you are the post owner or just reviewing and edit to some other post, checking the revision history for any post will reveal "rollback" links on each previous revision and at your discretion you can revert to an earlier version.
Here is how to access the revision history:

Click on the edited link above the user name that most recently edited at the bottom of the post.
That link is between your user name and the Share, edit, flag links.

And here is a sample that shows how you rollback a revision:

Once you click on the revision history link you will see all the revisions stacked on top of each other, starting with the most recent one.
You can click on the blue background to expand the text of previous revisions.
In the blue background of any previous revision are the links source, edit, and rollback. Clicking rollback changes the post exactly back to that particular revision.


Can I ask for a LOR from a teacher that didn't teach any of my classes?

Question: I want to do a Master's in CS, but I didn't do the undergraduate in CS, so I want to know if I can get a letter of recommendation from a professor that I know but who didn't actually teach me.
Comment: So.. if you didn't have any classes with the professor, what will they know about you and from where - i.e. did you frequently stop by his office to talk about a project of sorts, or were you involved in a club or student organization which he was a part of?
Comment: The deal with letters of recommendation is you've given the author some measure of critique of YOUR character. If all he has to write in this letter is "I knew this individual," there's simply nothing to recommend. Speak in office hours, let this person know your aspirations and abilities so that they have a gleaming letter to send on your behalf.
Comment: @Kendall: While it's not necessary for the interaction to be formal, it would be dishonest for a professor to send a "gleaming" letter concerning someone they just met, merely repeating things the student has told them.  Rome wasn't built in a day, and neither is a mentoring relationship.
Comment: Sometimes professors/researchers ask the candidates to draft a LOR and send it to them, as they are busy people, and would like to optimize their time. So put yourself on his/her shoes, and draft a recommendation letter for yourself from the point-of-view of the professor, if you are struggling to come up with anything concrete, then perhaps you should rethink whether to ask that person for LOR.
Comment: @BenVoigt I poorly worded that, it was my intention to allude that a developed relationship is what would lead to a good letter!
Comment: The only way to figure out is if you ask.
Answer: The general rule when it comes to letters of recommendation is that you should not ask for a letter from someone who does not know you well.
In this particular case, it's not sufficient that the professor you want to ask knows you. It is more important that he knows your work well, and can comment on that to graduate schools regarding your potential as a future student in their program.
Comment: I don't think this is true.  Letters aren't binary, it's not "letter or no letter".  Their length and content matter.  You can write a short letter confirming you think someone is bright or honest or whatever and worth a shot even if you only know them and not their work.  Not for a tenure-track faculty position obviously, but for a masters that might be sufficient.  If the student also has strong marks or good letters from an employer, having an academic say that they've talked to the student for an hour and they seem to understand what an MSc involves could be a useful plus to an application
Answer: You can get a letter from anyone who is willing to write one for you.  They will normally only say they will write the letter if they know something about you.  I've personally written letters a few times for students who had problems with their dissertation supervisor, and I knew something about their work for one reason or another, e.g. they'd tutored for me, I'd second marked their (undergraduate) dissertation, they've turned up regularly to research seminars and asked good questions or even given a talk, they've done research with me or my PhD students.  Actually, some of those can be more important than having taken a class with someone.
If someone asks me for a letter and I don't know them, if they just ask me because I'm well known in my field, and they can't say why they want me to write the letter, then I will tell them I can't write a strong letter. If I have time and they still insist, I write a letter that says "I can confirm that this is a student at my university, their GPA is [whatever, I look it up], and I have no idea why they asked me to write this letter."  Depending what you need the letter for, it's possible that would be enough.
A better plan would be to exploit office hours, sign up and visit a few times, discuss (first read!) their papers, and then asks for a letter.  Then the letter might be made stronger by the impression you've made.
Answer: Keep in mind the overall goal -- you want to convince the admissions committee that you're a great student, and would do well in their program.
Of course you can point out your own strengths yourself, but it's even better if someone they trust testifies to your strengths. If the person your asking hasn't seen your strengths personally, they won't be able to write a personal letter attesting to them.
So get to know people, either by going to office hours (as said above), taking a class, taking up a side project, or working for them.
If you want to stick with people you already know, you should be aware yourself about how your background in ___ prepared you for a CS degree, or shows you're likely to succeed. If you can let the recommenders know how they can help and why you chose them, they might realize they can help rather than thinking they cant.


Is it possible to have an angle of incidence for a vertical stabilizer?

Question: horizontal surfaces in airplane have small angle of incidence in general, Is it possible to have an angle of incidence for a vertical stabilizer?
Please help me to find it. Thanks!!
Comment: NO :the angle of incidence (sometimes referred to as the mounting angle[1]) is the angle between the chord line of the wing where the wing is mounted to the fuselage, and a reference axis along the fuselage (often the direction of minimum drag, or where applicable, the longitudinal axis). The angle of incidence is fixed in the design of the aircraft, and with rare exceptions, cannot be varied in flight.
Comment: You may be french-speaking. In English, you usually use "angle of attack" while in French you use "angle d'incidence"
Answer: Some vertical stabilizers will have a slight angle of incidence to counter left turning tendencies. Older model Cessna 172s and 150/2s have a little metal trim tab that can only be adjusted by manually bending it from the outside. This will serve to adjust the vertical airfoil chord line angle in the aircraft slipstream or relative wind. The degree of incidence will be manufacturer and model specific.
Answer: Yes, but the term "incidence" normally only applies to horizontal surfaces. With a fin it's usually called "fin offset" and is very common on single engine tractor aircraft.
The offset helps align the fin into the spiraling airstream coming off the prop so that a counteracting rudder input isn't required (or at least a smaller input is required) to counteract the offset slipstream trying to push the tail to the side.  It's usually 2 or 3 degrees to the left for an engine turning clockwise from the cockpit where the flow at the fin leading edge is coming from the left, or to the right for an engine that turns counterclockwise.
It's very common but not universal.  Some airplanes just use a fixed trim tab on the rudder to passively do the same thing, or both a tab and an offset fin.
They also often have the engine offset several degrees on the mount, to the right on a clockwise engine.  Look at single engine airplanes from above and it becomes quite apparent how the engine/prop is crooked as well as the fin being angled to the side, like the plane got into a fender bender accident and just drove off like that.  Makes you wonder how the dang things fly straight in the first place.
Answer: I'm no expert, but Wikipedia helps. The angle of incidence is the angle between the chord line and a reference line on the fuselage. [source] Since the vertical stabiliser is on a different geometric plane, there can't be an angle of incidence as there is with the wings.
Comment: FYI, a vertical stabilizer has a chord line. It usually has not much of a net camber. But, it is not perfectly flat. A reference line would imply a 1 dimension aspect. The wings have an angle of incidence to a 2D plane on the aircraft represented by the ref line. The vert stab would have an AoI to a different plane represented by the same or a different ref line. The best ref line to use for both would probably be the longitudinal axis of the aircraft.


What is a quantum computing attack?

Question: As far as i know, a quantum attack is a brute force attack performed by a quantum computer. source: wiki
Is this very simple definition correct ? or the scope of a quantum computing attack is bigger.
Answer: No, it's an attack using algorithms such as Shor's algorithm that cannot be efficiently executed on conventional computers. A sufficiently powerful quantum computer can factor an integer in polynomial time, and many encryption algorithms rely on the difficulty of factoring large numbers.
Answer: First of all, a very big NO.
Saying that a Quantum Computer (QC) simply performs a lot of actions (in this case brute forcing) simultaneously to get the results quickly is a misconception. Quantum Computer doesn't brute force over the available set of actions in order to find the answer. QCs doing a lot of things simultaneously is due to the fact that it is in a superposition state of exponentially many states. NOT that the processor is working very very fast on many different things at the same time. You can find more about how it does it is the link provided below. Apart from that, the logic gates are fundamentally different for QC. In classical computer all logic gates except the NOT gate are irreversible while for QC all gates are reversible.
QCs are fundamentally different than our classical computers as they rely on qubits (instead of bits). One qubit can be in 0, 1, or both at once (superposition of both). Two qubits can represent four states simultaneously, while a hundred qubits can represent 1.3 quadrillion quadrillion states. This allows QCs to find pattern in the data set very quickly.
Asymmetric cryptosystems' security depends on unfeasible factoring of very big numbers by classical computers. While for the QCs it is just a matter of time.
Go over my this answer on Quora. It has a full explanation of what you are looking for plus more. Don't really feel like repeating everything.
Answer: Old topic but Grovers algorithm should be mentioned. With this algorithm it is possible to search an unsorted database faster than linear which means that with grover it could be possible to have more efficient brute force attacks.
https://en.wikipedia.org/wiki/Grover%27s_algorithm
A side note: this is also very interesting in the field of machine learning. For example the storage capacity of neural networks for pattern recognition increases with Grover's quantum neural networks (in analogy to a quantum bit the neuron could fire, not fire or be in a superposition of fire and not fire [as long nobody measures because if you measure/look (or even have the possibility to look) the system loses it's quantum behavior due to decoherence]).
You can play on your own. IBM gave access to their old quantum machines so you could experiment with real quantum technology and not "only" simulated quantum behavior. All you need is an account (which is free) and Python. Take a look ;)
IBM: https://quantumexperience.ng.bluemix.net/qx/experience
Python: https://qiskit.org/
Comment: This answer, too, does not answer the question. Please make sure your answers address the question directly. This is a Q&A site, not a discussion forum.

What is a quantum computing attack?


Test your Mobile App's Code

Question: I am new to game development in HTML5, and I would like to know how I can test my code out to see what I made with an IDE or something. Thanks!
Comment: I imagine this is covered in any basic tutorial. What have you looked for already?
Answer: You should be able to load HTML5 in a web browser or an appropriate emulator or it's targeted toward a specific device

Test your Mobile App's Code


Why green leaf turns brown in Brine solution?

Question: I immersed a semi dry green leaf in glass of concentrated NaCl solution . I left it in mild sunlight for around 3 hours . Solution before was clear but afterwards it became reddish brown and the color of leaf turned brown. I want to know why this happened? Please help.
Answer: It is most likely the $\ce{Na+}$ is formed a complex salt with chlorophyll (bulky group) subsequently displacing $\ce{Mg+}$ cation, even though $\ce{Na+}$ doesn't have extra electronic shells for complex ion stabilisation, instead the chlorophyll (through the $\ce{N}$ atoms with lone pairs) provided extra stabilisation of the positively charged $\ce{Na+}$ cation.
Chlorine dissociated from $\ce{NaCl}$ to form aqueous chloride ions $\ce{Cl-(aq)}$ forming a typically greenish-brown solution you noticed during your experiment.
Comment: Are you saying that chloride ion is greenish brown? If so, why is a sodium chloride solution not brown?
Comment: Not necessarily, because when isolated it exist as pale greenish-brown gas, however due to the presence of different molecules and aqueous environment several solvents are present together with the chloride ions, and may inhibit the Chloride ions to explicitly show it's typical greenish-brown colour, remember other minor products are also present in solution with the Cl- ions.  Also to note in the leaves there is also Fe³+ ions , subsequently can be attributed to the overall color of solution, if we to extract all the "impurities" to leave only chloride ions we would get a color close to green
Comment: NaCl would not be green because of the lack of "outer shells with vast electrons" so would not get excited to 3d states where it absorbs light, emit some to produce color like what transition elements do. For our complex solution above, the chlorophyll group ( with N lone pairs of electrons) allowed the complex salt to be activated hence emit some light energy to produce color.


Foursome intercourse with consent?

Question: Someone asked me a very confusing question.
That if any husband and wife are agree to have intercourse with other husband and wife with each other at the same time in the same room, is it halal in Islam or not?
Please shed some light on this issue if anyone knows about this.
I already told him it's haram but I don't have any proof.
Comment: https://islamqa.info/amp/en/answers/82994 According to this you can't even look at non mahatma awrah never mind having sexual intercourse.
Comment: It is adultery and haram.
Comment: I need to proof him
Comment: Just literally write adultery in Islam or something like that
Comment: Proof that adultery is haram?
Answer: The proof is crystal clear in the qur'an:

And they who guard their private parts (5)
  Except from their wives or those their right hands possess, for indeed, they will not be blamed - (6)
  But whoever seeks beyond that, then those are the transgressors - (23:5-7)

And those who guard their private parts (29)
  Except from their wives or those their right hands possess, for indeed, they are not to be blamed - (30)
  But whoever seeks beyond that, then they are the transgressors - (70:29-31)

So who ever gets intimate or had intercourse with a woman, which he didn't marry (in first place), is committing zina and Allah tells us:

And do not approach unlawful sexual intercourse. Indeed, it is ever an immorality and is evil as a way. (17:23)

Beyond this if a husband asks his wife to do this she is allowed to disobey as Allah says -protecting slave girls!-:

... And do not compel your slave girls to prostitution, if they desire chastity, to seek [thereby] the temporary interests of worldly life. And if someone should compel them, then indeed, Allah is [to them], after their compulsion, Forgiving and Merciful. (24:33)

So protecting married (free) woman should have at least the same level of imporance in Islam.
Finally note that a man is not even allowed to have sex with two of his wives at once in one bed (not mentioning the case of a foreign woman and man sharing it with him and his wife) (See for example: Is a Muslim husband allowed to have sex with his multiple wives simultaneously?). Because Islam has put boundaries to keep us clean and pure these are the rules of mahram-ship which order us to dress differently accoridng different cases like being alone with our spouses or with  mahrams or with foreign people and anybody who is not a mahram is considered a foreigner.

Foursome intercourse with consent?


What minimal resistance should be between an input and output pin not to burn Arduino?

Question: So, I'd like to put a button between input and output pins to read when button is pressed. What minimal resistance should I add to the scheme not to burn Arduino when the button is pressed? Does this value depend on Arduino model?
Comment: Why between an input and output? Have you read the Button tutorial on the Arduino site? https://www.arduino.cc/en/Tutorial/Button
Comment: @Majenko I see, it should probably be "what minimal resistance should be between ground and 5V", I guess..
Comment: @Majenko to make sure I understand you correctly, I've asked another question: http://arduino.stackexchange.com/questions/22672/is-that-correct-that-input-and-output-pins-are-not-supposed-to-have-current-thro
Comment: @YakovL - posting additional closely relations questions is frowned upon, it is better to edit the existing question.
Comment: @ChrisStratton I was going to edit this question after I get an answer to that other question, and "correct" question would be "What minimal resistance should be between 5V and GND pins not to burn Arduino?", but as you have answered this first formulation, I'm not sure what would be more appropriate now..
Comment: "What resistance should be between 5V and GND" pins  has nothing to do with the Arduino's processor, but only its power supply.  It's also a rather pointless question as putting a resistor there does little but drain the power supply capacitor once the supply is off.
Answer: Looking towards the high end of recommended (vs absolute maximum) current and considering Ohm's law at a 5v difference if two outputs are trying to drive each other to opposite values, you would probably get away with as little as 250 ohms.  But in most cases that would needlessly waste power, and in the case of multiple instance you could start totaling towards the limit of power supply current for the chip overall.
Typical values for external pull up resistors are more in the range of 1K-10K though higher is not uncommon - the internal pullup which you can optionally activate by setting the output state of an input pin high has a value of several tens of kilo ohms.  Lower values will consume more power, higher values may be less reliable in a noisy situation.
Answer: To read a button, normally you hook one end of the button to ground and one end to a pin in INPUT_PULLUP mode. Normally the pin reads 'high' because it is connected to +5v with a biggish resistor inside the arduino. When you press the button, it shorts out to ground and the input reads 'low'. The chip already has suitable resistors in it to handle this, and you don't need to worry about it. Just connect one end of your button the the pin, the other to the chassis, INPUT_PULLUP and away you go.
Output pins should have no less than 250Ω on them.
Beats me why you are thinking of connecting an output pin and an input pin together.


Will one become a kafir because of his minor shirk?

Question: Will one become a kafir because of his minor shirk and permanently reside in the hellfire?
Comment: If someone who did minor shirk and became kafir then why is it called minor shirk? Isn't it major shirk then?
Answer: No, not necessarily!
Minor shirk, like doing any action with an intention other than exclusively for Allah, can be very difficult for most people to avoid. It can be subtle, hidden, accidental, or fleeting. Even many people who believe in Allah are guilty of it:

وَما يُؤمِنُ أَكثَرُهُم بِاللَّهِ إِلّا وَهُم مُشرِكونَ
And most of them do not believe in Allah without ascribing partners to Him. [Yusuf, 12:106]

It does not imply kufr! And it certainly does not guarantee eternal punishment.
If you catch yourself committing shirk (minor or major), perhaps while in a state of heedlessness, correct your intentions/behaviour and seek forgiveness.

إِنَّ الَّذينَ اتَّقَوا إِذا مَسَّهُم طائِفٌ مِنَ الشَّيطانِ تَذَكَّروا فَإِذا هُم مُبصِرونَ
When those who are Godwary are touched by a visitation of Satan, they remember [Allah] and, behold, they perceive. [al-A'raaf, 7:201]

Allah can forgive any sin, including shirk (even the major kind!), if the person repents from it.

قُل يا عِبادِيَ الَّذينَ أَسرَفوا عَلىٰ أَنفُسِهِم لا تَقنَطوا مِن رَحمَةِ اللَّهِ ۚ إِنَّ اللَّهَ يَغفِرُ الذُّنوبَ جَميعًا ۚ إِنَّهُ هُوَ الغَفورُ الرَّحيمُ
Say [that Allah declares,] 'O My servants who have committed excesses against their own souls, do not despair of the mercy of Allah. Indeed Allah will forgive all sins. Indeed He is the All-forgiving, the All-merciful. [al-Zumar, 39:53]

Also, be grateful to Allah for making you aware of your flaws and giving you a chance to correct them while you still have a chance.


What is the difference between white and pink ginger?

Question: Some sushi places serve white ginger flakes with their food, while others serve pink colored ginger. There doesn't seem to be any detectable taste difference that I've found. So, what is the difference between the two other than just color, and, why serve one over the other?
Answer: Although white ginger and red (or pink) ginger do exist, the different colors in sushi ginger are from a dye. The color in white sushi ginger comes from the pickling process and the red/pink color in ink sushi ginger comes from an artificial dye (usually E124 -cochineal red- or in other brands beet extract). The generic name for sushi ginger is gari and here's the Wikipedia page.

White gari/sushi ginger on the left and pink gari/sushi ginger on the right.
Comment: Worth noting that traditionally, the pink colour would come from red perilla (shiso) leaves, and thus would have a subtly different flavour
Answer: The bright pink ginger is pink because of food coloring.
http://chowhound.chow.com/topics/599069
http://www.alibaba.com/product-gs/514063793/Pickled_Sushi_Ginger.html?s=p
Answer: Salt and acids (in the case of pickled ginger, vinegar and citric acid) turn ginger pink during the pickling process naturally. However, this hue will eventually fade to pale yellow and then brown in less than 3 months as the ginger gets exposed to UV light and heat. This is why food coloring is added to the pink variety. As for the yellow/white pickled ginger, sodium metabisuphite must be added to stop the product from turning brown. This sulphite is an allergen and must be accordingly labeled.
If you want to preserve the natural pinkish hue of the pickled ginger, keep the product refrigerated at 2 degrees Celsius. Away from UV light and heat, the color will remain for up to 1 year.


Want to be fair to potential employer

Question: I've been offered a job ("JOB A") while waiting to hear on another job ("JOB B").  JOB A is a sure thing and they are just waiting to hear back from me as to whether or not I'll accept.  JOB B felt like a sure thing at one time but they have pushed the start date back again and again for two months now and I'm starting to wonder if it will ever happen. JOB A is a permanent job but only pays about ½ as much as JOB B which is an 8 week contract-to-hire job.  Is it alright to accept JOB A knowing that if JOB B comes along I will have to quit at a moments notice?  I really like the people at JOB A and they are very excited about the possibility of having me work for them.  I just don't feel right accepting JOB A unless I totally forget about JOB B.  Also, I've been out of work for about 4 months and really need to get some money coming in.  What to do?  What to do?
Comment: Your feelings on this are well founded. It would be completely unethical to take Job A if you're willing to cast it aside as soon as you hear back from B. Understandable that the prospect of a much higher rate tempting, having said that. I think you already have one solid answer, hopefully you'll get more.
Answer: From your description, job B has nothing for it except the higher pay and doesn't even guarantee conversion to full-time. They could bait-and-switch you to lower salary once FT. (Been there). Especially given the 4 months off.
Just accept A already. Or go back to A, tell them you are excited by the opportunity, but mention that a competing offer, while not as interesting, if offering significantly more. Raising their offer slightly would cast away any lingering doubt you have. See what you can get. Stay polite and positive, simply mention that a slight increase in the offer would seal the deal.

Want to be fair to potential employer


Photoshop union shapes doesn't show up for SVGs

Question: I have two shapes that I unioned together in Photoshop to create this red outline. When I export as an SVG, it exports the red outline as two separate shapes. Flattening or rasterizing the outline causes the SVG to treat the outline and the image as one whole image. Is there any way to get around this? I need the red outline to be an SVG and the image could be svg, png, anything.
Comment: Unrelated to the question and... I don't know how you made the outline but it looks a little freehandy... To potentially shorten and simplify the workflow in PS you could Ctrl+click the layer thumbnail to get selection of the layer (with no bg), expand the selection, and [convert the selection into a path](https://helpx.adobe.com/photoshop/using/converting-paths-selection-borders.html#convert_a_selection_to_a_path). Or in AI you could auto trace the image and use the "silhouette" preset to get the outline of the person or horse or whatever that is, and then offset it outwards.
Comment: yes, this was made using expand and converting to path
Answer: Looks like you have only Combined the shapes, meaning they are still different paths.  You need to Merge Shape Components.
Example


How to pause a process until memory requirements drop

Question: I'm compiling source code in the terminal but 75% of the time the build will freeze my system and I have to hard reboot or wait for a LONG time until oom kills it. I'm positive it's a memory issue because I leave system monitor running on top and watch it throughout the compilation. Everything runs fine until ram/swap usage is maxed out and then freezes where it is and the CPU use drops back down to zero. I have 4gb of ram and have tried running builds with swapoff and also switching swap size to between 400 mb and 2 gb and the problem still persists. Iwas wondering if I can possibly pause the process until the ram is cleared instead of just killing it?
Comment: what are you trying to compile? This is a strange situation --- are you sure you are not using a full parallelized make (like `make -j`?) - in that case just limit the number of parallel tasks (hardly anything over `make -j4` helps, unless you have a monster machine).
Comment: I haven't built Android, but I'm assuming you're doing so from the root directory, is that correct? Is there a way that you can break the process into more manageable chunks? What I'm thinking is that maybe make itself is keeping resident memory for what I would imaging would be a lot of sub-jobs -- memory that it would keep resident until the relevant piece or group of pieces is finished with their sub-make. However, if you could break it down into smaller jobs, perhaps you could avoid the oom issue.
Comment: @Githlar not running from the root but a sub directory ~/android/build. I split off about 25% by building the kernel separately but thats about all I can do in split jobs AFAIK. Periodically I tried turn swap on and off during the build to free up space for then end. It is near the end of the build process just before everything starts to be packaged into the final compilation that it hangs (yes the most memory/process intensive task).
Answer: Somebody already did it here https://unix.stackexchange.com/questions/68611/whats-the-difference-between-ctrl-z-and-kill-stop

When I run a command (make on a large project) from the shell, I can
  type Ctrl-Z to stop the process and return to the shell. Subsequently,
  I can run fg to continue the process.

I am not sure though if the RAM will auto-clear.
Comment: The RAM does not clear until the process is finished, so suspending doesn't release RAM. However, it might help swap since it can take substantially longer to clear than RAM.
Comment: @rmano thanks but i am not using an unlimited -j, I was only using -j2, -j3, or -j4. And I'm compiling android
Comment: @Githlar the process isn't running anymore though, once the memory hits 100% the whole system freezes and is unresponsive until it gets killed or i hard reboot.
Comment: I understood what you meant by oom. I was just saying that his answer doesn't really fix the problem necessarily. However, since swap is also an issue for you, suspending occasionally may give the kernel time to dump swap. Time that it might not have otherwise because of the quick pace of the make process, thus perhaps preventing the oom to some degree.
Comment: @f01 Will ctrl-z and fq allow it to finish up the most recent process thus freeing up some ram? I'm upgrading to 8 gb of ram soon so that should hopefully help a lot


Java immutable strings confusion

Question: If Strings are immutable in Java, then how can we write as:
String s = new String();
s = s + "abc";

Comment: s is not the string, it's a container which holds a reference to a string. First, it holds the reference to the string returned by new String(), then it is changed to hold the reference of the string which is returned by new String() + "abc" i.e. the reference of another string.
Answer: Strings are immutable.
That means that an instance of String cannot change.
You're changing the s variable to refer to a different (but still immutable) String instance.
Answer: Your string variable is NOT the string. It's a REFERENCE to an instance of String.
See for yourself:
String str = "Test String";
System.out.println( System.identityHashCode(str) ); // INSTANCE ID of the string

str = str + "Another value";
System.out.println( System.identityHashCode(str) ); // Whoa, it's a different string!

The instances the str variable points to are individually immutable, BUT the variable can be pointed to any instance of String you want.
If you don't want it to be possible to reassign str to point to a different string instance, declare it final:
final String str = "Test String";
System.out.println( System.identityHashCode(str) ); // INSTANCE ID of the string

str = str + "Another value"; // BREAKS HORRIBLY

Comment: No, it doesn't. Methods in Java are virtual, casting an object to a super type has no effect here. The `String`'s overriden `toString() `method implementation will still be called. You need to call `System.identityHashCode(str)` in order to get the original identity based hashCode of an object.
Comment: Simple. str.toString() returns... the string. Calling ((Object)str).toString() gives us the actual instance ID. This is for demonstration purposes.
Comment: Argh! Thanks for the tip. I should have tried the code before posting it. Adjusting the post to reflect.
Answer: The first answer is absolutely correct. You should mark it as answered.
s = s+"abc" does not append to the s object. it creates a new string that contains the characters from the s object (of which there are none) and "abc".
if string were mutable. it would have methods like append() and other such mutating methods that are on StringBuilder and StringBuffer.
Effective Java by Josh Bloch has excellent discussion on immutable objects and their value.
Answer: Immutable Classes are those whose methods can change their fields, for example:
Foo f = new Foo("a");
f.setField("b"); // Now, you are changing the field of class Foo

but in immutable classes, e.g. String, you cannot change the object once you create it, but of course, you can reassign the reference to another object. For example:
String s = "Hello";
s.substring(0,1); // s is still "Hello"
s = s.substring(0,1); // s is now referring to another object whose value is "H"

Answer:    String s = new String();

Creates a new, immutable, empty string, variable "s" references it.
   s = s+"abc";

Creates a new, immutable, string; the concatenation of the empty string and "abc", variable "s" now references this new object.
Answer: Just to clarify, when you say   s = s+"abc";
That means, create a new String instance (which is composed of s and "abc") then assign that new String instance to s. So the new reference in s is different from the old.
Remember, a variable is effectively a reference to an object at some specific memory location. The object at that location stays at that location, even if you change the variable to refer to a new object at a different location.
Answer: String s = new String();

An empty String object ("") is created. And the variable s refers to that object.
s = s + "abc";

"abc" is a string literal (which is nothing but a String object, which is implicitly created and kept in a pool of strings) so that it can be reused (since strings are immutable and thus are constant). But when you do new String() is totally different because you are explicitly creating the object so does not end up in the pool. You can throw is in the pool by something called interning.
So, s + "abc" since at this point concatenation of and empty string ("") and "abc" does not really create a new String object because the end result is "abc" which is already in the pool. So, finally the variable s will refer to the literal "abc" in the pool.
Answer: I believe you are all making this much more complicated than it needs to be, and that simply confuses people who are trying to learn!
The primary benefit of making an object immutable in Java is that it can be passed by reference (e.g. to another method or assigned using the assignment operator) without having to worry about downstream changes to the object causing issues in the current method or context. (This is very different than any conversation about the thread safety of an object.)
To illustrate, create an application that passes a String as a parameter to a separate method, and modify the String in that method. Print the String at the end of the called method and then after control returns to the calling method. The Strings will have different values, and that's because they point to different memory locations, a direct result of "changing" the immutable String (creating a new pointer and pointing it to a new value behind the scenes). Then create an application that does the same things except with StringBuffer, which is not immutable. (For example, you can append to the StringBuffer to modify it.) The printed StringBuffers will have the same values, and that is because it is (a) being passed by reference, as Java does with all objects passed to methods as parameters and (b) mutable.
I hope this helps folks who are reading this thread and trying to learn!

Java immutable strings confusion


Are all gold saints supposed to be equally strong?

Question: I've read some comments in internet where they refered to a supposed answer of the creator of Saint Seiya stating that all saints were equally strong. Is this true? This doesnt seem to be what's shown in the series and what fans in general think is saints like Shaka and Saga are usually ranked higher.
Answer: Unless there's an interview I'm not aware of, Kurumada never said that.
What he said is that what he really cared about was trying to create them all cool and powerful, but even him cannot say which one is the strongest.
You can check that here.
Answer: Just thinking at the manga and anime stories, I can say that Saga has much more power that all the other Gold Saints. I am saying this because he is able to force most of them under his will. He is also able to control a couple of puppies saint while he is still in the Grand Master Hall.
Then he is also able to confront and resist to multiple attacks from some gold saints together.
Comment: I agree with part of your arguments, but we have to remember that authority is not a physical force itself ;) but it is like a social force, and, really, it represents more power than the brute force since you can sum all the physical forces of it's followers as his resource.
Comment: I.e., it is a different comparison between the whole power of each one in anime/manga and the power in a man-vs-man combat in a normal-temperature-and-pression-condition-isolated room :)


What is $\lim _{x\to \infty }\left(\frac{e^x}{x^n}\right)$?

Question: What is $\lim _{x\to \infty }\left(\frac{e^x}{x^n}\right)$
?
Comment: It diverges to infinity.
Answer: Recall that
$$
e^x=\sum_{k=0}^{\infty}\frac{x^k}{k!}=1+\frac{x}{1!}+\frac{x^2}{2!}+\ldots+\frac{x^n}{n!}+\ldots
$$
then, for each fixed $n$, as $x \to +\infty$, you get
$$
e^x>\frac{x^{n+1}}{(n+1)!}
$$ and
$$
\frac{e^x}{x^n}>\frac{x}{(n+1)!} \longrightarrow +\infty, \quad\text{as} \quad x \to +\infty,
$$ and the desired limit is $ +\infty$.
Answer: The limit is $+\infty$.
One way to see that is to use L'Hopital's rule. Differentiate numerator and denominator $n$ times, and you get
$$\frac{e^x}{n!}$$
which clearly diverges to positive infinity.
Answer: Exponential function increases faster than any polynomial function. You can imagine it this way - an exponential function consists of polynomials of progressively higher and higher degrees summed together. For any degree $n$ polynomial you are comparing against, exponential will have terms of degree $n+1$ and beyond too. (Agreed with progressively smaller coeffs, but eventually you are taking the limit $x \rightarrow \infty$, so that's hardly helping!)
As $x \rightarrow \infty$, the numerator increases much faster than the denominator, and the expression diverges (tends to $\infty$).
Answer: Another possibility:
$$\lim_{x\to\infty}\left(\frac{e^x}{x^n}\right)=
\lim_{x\to\infty}\left(\frac{e^{x/n}}{x}\right)^n=
\left(\lim_{x\to\infty}\frac{e^{x/n}}{x}\right)^n=\cdots$$


Button for adding an instance of formset in Django

Question: I want to create a button for dynamically adding and removing an instance of formset from the displayed page. It is my first experience with formset in Django and I do not know any JavaScript, so I would be grateful for any help. So, lines for the formset in my view look like this:
strategy_settings = formset_factory(StrategySettings, extra=1)
strategy_form = strategy_settings(request.POST)

I believe it is a matter of changing the value of an "extra" attribute, but I do not know how to achieve it in JavaScript.
here is my template:
{% extends "mainapp/base.html" %}
{% block content %}
<form method="post" id="strategy-form">
    {% csrf_token %}
    {{ simulation_form.as_p }}
    {% for form in strategy_form %}
    {{ form.as_p }}
    {% endfor %}

    <button type="button">Add Strategy</button>
    <button type="button">Remove Strategy</button>

    <button type="submit" name="save">Submit</button>
</form>

{% endblock %}

Thanks to anyone in advance.
Answer: The extra value determines how many additional, empty forms are displayed initially.
As for the dynamic stuff, since you don't know any javascript (yet), I suggest you look into a 3rd party package that does what you want. For example here: https://djangopackages.org/search/?q=formset.