Does the magnitude of a physical quantity have units or is it just a plain number?

Question: Does the magnitude of a physical quantity have units? For example, if a velocity vector is $36\ \mathrm{m\,s^{-1}}\ \hat{u}$, is its magnitude $36\ \mathrm{m\,s^{-1}}$ or just $36$? Also why?
Answer: The magnitude has units. In your example, it's physically how fast you're going, which is measured with units. It doesn't make sense to say you're going "36", and so it doesn't make sense to say the magnitude of your velocity vector is 36.
Saying that the magnitude is 36 is a bad idea, because if you measured in cm/s instead, the magnitude would be 3600, and the magnitude would change depending on what units you had. Instead, we attach units to the magnitude so it can be expressed as 36 m/s or 3600 cm/s, but these are the same quantity, so the magnitude doesn't change with different units. It's a property of the vector, not an accident of the units chosen.
Comment: Incidentally, we can also arrive at the same result from the opposite side: After decomposing into magnitude and direction vector, the latter should have magnitude 1, but 1 is dimensionless.  It wouldn't make sense to have units in your direction vector, so they have to live in the magnitude instead.
Comment: @Kevin I'm actually not so sure about that. I think you could develop a perfectly good mathematical system where units are kept in the direction vector (so it would really be a "direction-unit vector"). The problem is just that it would be less useful than a system where the units are kept separate, because you'd need different unit vectors for different types of quantities.
Comment: @Kevin - I agree. Geometry => the science of measuring the world. To measure the world we use various "yardsticks". A measured distance is a scalar multiple of some agreed upon yarstick and the scalar multiple doesn't carry the units, the yardstick does. It is not just a random stick, it is of a specific measure.
Comment: [Can "speed" be a unit?](https://i.imgur.com/puYcLhl.jpg)
Answer: It makes sense to assign the units to the magnitude and not the direction vector, but it would work either way.
Consider the position vector denoted by $$ \boldsymbol{r} = \pmatrix{ 3\, {\rm m}\\ 2\, {\rm m}\\ 6\, {\rm m}} = \pmatrix{3\\2\\6} {\rm m}  $$
The magnitude of the vector is $ \| \boldsymbol{r} \|  = 7 {\rm m} $, but to decompose it into magnitude and direction we have a choice:
$$ \boldsymbol{r} = (7 {\rm m}) \,\pmatrix{ \frac{3}{7} \\ \frac{2}{7} \\ \frac{6}{7} } = (7) \,\pmatrix{ \frac{3}{7}\,{\rm m} \\ \frac{2}{7}\,{\rm m} \\ \frac{6}{7}\,{\rm m} } $$

The first being the distance $7 \,{\rm m}$ in the direction $\left(\frac{3}{7} , \frac{2}{7} , \frac{6}{7}  \right)$. This is the span interpretation when one spans "x" distance along a particular line.
The second being 7 times the distances $\left(\frac{3}{7}\,{\rm m} , \frac{2}{7}\,{\rm m} , \frac{6}{7}\,{\rm m}  \right)$. This is the ruler interpretation, where one moves "x" number of ticks in more direction and each tick has units.

In fact, there are cases where both the magnitude and unit vector may contain units. For example, consider a planar force acting along a line. Now combine the force components with the equipollent torque at the origin.
$$ \boldsymbol{f} = \left[ \matrix{ \vec{F} \\  \tau } \right] = \left[ \matrix{6.9282\,{\rm N} \\ 4.0 \,{\rm N} \\ 20.0 \,{\rm N\,m}} \right] = (8.0\,{\rm N}) \left[ \matrix{ 0.866 \\ 0.5 \\  2.5\,{\rm m} } \right] = F \,\hat{\ell} $$
The magnitude of the force is $F = 8\,{\rm N}$, acting along a line with equation  $a y - b x + c =0$ where $\hat{\ell} = (a,b,c) = (0.866, 0.5, 2.5)$ and the direction vector $(a,b)$ has unit magnitude $\sqrt{0.866^2+0.5^2}=1$ and thus $c=2.5$ is a distance quantitiy (for $ay-bx+c=0$ to be dimensionally accurate).
Comment: Stating @JiK's point more strongly, I would disagree with this answer. The magnitude is $7\rm{m}$, and that doesn't become negotiable when we "decompose it into magnitude and direction". As such, a direction vector should always have unitless magnitude $1$. (A caveat: I am not a physicist, so it's possible that this is something where physics conventions differ from what would be common in math, so I am refraining from voting.)
Comment: Why did you pick out "7 times the distances $\left(\frac{3}{7}\,{\rm m} , \frac{2}{7}\,{\rm m} , \frac{6}{7}\,{\rm m}  \right)$"? It's no more special than "14 times the distances $\left(\frac{3}{14}\,{\rm m} , \frac{2}{14}\,{\rm m} , \frac{6}{14}\,{\rm m}  \right)$"
Comment: @JiK I'm guessing the reason for choosing $\left(\frac{3}{7}\,{\rm m} , \frac{2}{7}\,{\rm m} , \frac{6}{7}\,{\rm m}  \right)$ is that it's a "unit vector" - not in the usual sense, but in the sense that its magnitude is equal to the chosen unit of length, namely $1\ \mathrm{m}$. On the other hand $\left(\frac{3}{14}\,{\rm m} , \frac{2}{14}\,{\rm m} , \frac{6}{14}\,{\rm m}  \right)$ doesn't have the same property. I also disagree with this answer along similar lines to what Mark said, but I do think I see the logic behind it.
Comment: @JiK - The function of a ruler is to describe the scalar multiple of a unit dimension. Such as "three and a half times one inch" for $3.5\,{\rm in}$. Similarly, the notation $7\;\left(\frac{3}{7}\,{\rm m} , \frac{2}{7}\,{\rm m} , \frac{6}{7}\,{\rm m}  \right)$.
Comment: @DavidZ - when I first thought of this issue, I was like you, in that it was preposterous the assign units to basis vectors. But after some work in projective geometry, I realized that mathematically the two interpretations are identical (dual to each other).
Comment: @DavidZ - in physics there are vectors (with a physical interpretation) where not all the components have the same units. In that case, the magnitude is just a scalar value, and the unit vector carries the units.
Answer: You would quote the speed as $36  \, \rm m\,s^{-1}$ because it is $36$ times $1  \, \rm m\,s^{-1}$.
If you wrote just $36$ what would that mean?
$36$ times what ????
Now what about $36  \, \rm m\,s^{-1}\, \hat u$?
All you have now is extra information about the direction of the velocity and there is no extra information about the magnitude (speed) which is still $36  \, \rm m\,s^{-1}$.
Answer: A velocity vector is some 'arrow' in a mathematical space (Euclidean) which we denote with $\mathcal{R}^3$. The velocity vector is a physical object so therefore we use three dimensions (assuming non-relativistic). This means that we can write:
$v=\sum^3_{i=1}v^ie_i=v^1e_1+v^2 e_2+v^3e_3 \in \mathcal{R}^3$ (the symbol $\in$ means that $v$ is an element of $\mathcal{R}^3$) where $v^i$ is the component in one of the directions so for example the x-direction, which we denote by $v^1=v_x$ and $e_i$ the basis vector in that direction (a standard basis consists of orthonormal vectors, this means that the vectors are geometrically orthogonal and that they have unit length). So what you are doing is write the velocity vector in terms of these basis vectors, and of course in three dimensions you have three basis vectors (imagine up,right and straightforward).
However you are talking about numbers, this means that you talk about the length of the vector. The length of a vector is given by the following equation:
$||v||=\sqrt{(v^1)^2+(v^2)^2+(v^3)^2}=\sqrt{v_x^2+v_y^2+v_z^2} \in \mathcal{R}$.     (1)
$\mathcal{R}$ denotes that it is a (real) number. So once you know for example that the velocity of an object is 36 (=$||v||$). This could really mean anything. The units are arbitrary in mathematics. But of course not in physics. 36 here just means that the numbers corresponding to $v_x,v_y,v_z$ without mentioning units (however we do assume the same units) add up to this number according to equation (1). Once you know for instance that $v_x=10m/s,v_y=1m/s,v_z=0$. For $v_z$ I ignore the units since it is zero for every choice of (velocity) units. In this case the total velocity (see equation (1)) will be $||v||\approx 10.05m/s$ since $\sqrt{(10m/s)^2+(1m/s)^2}=\sqrt{10^2+1^2+0^2}m/s\approx 10.05 m/s$.You see of course that we could just say $||v||=\sqrt{10^2+1^2+0^2}\approx 10.05$ and look for the units afterwards, this is the math way (and advanced physics) of dealing with units.
So take away from this that a vector is not a number/scalar but an object which has a length which is a scalar.
Answer: Some people here seem to be getting hung up on vectors, though they really don't have anything to do with the question. There just happens to be a vector used as part of the use case example, but that is extraneous information which is irrelevant to the question and its answer.
Yes, a quantity has units.

I went to the store earlier and I bought 4.
Four what?
Oh, sorry... I bought 4 apples.

Now an example that is closer to yours:

Do you know why I stopped you?
No sir, I'm not sure. The sign reads "Speed limit: 45" and my speed
  was 41.
That is not true. You were doing 65.
[much arguing and time later...]
So you see sir, I was doing 45 miles per hour. If your city dislikes
  the units that the rest of the country uses, you need to state on your
  signs that the speed limit is 45 kilometers per hour.

That last example also leads us into a good (but false) counter point. Quantities are often given without units. In reality, even a sign which reads only "Speed Limit 65" is providing units even though it does not look like it.
Whenever we are talking, listening, reading, or writing there is practically always a context. Speed limits in the United States are known and understood to be provided in miles per hour even if not specified on the sign. Even if not written the "Speed Limit 65" sign still has units of miles per hour, so the units are provided.
Now let's jump over to a super technical science lab setting. A pair of workers are taking measurements, and one of them asks "How high is it this time?" The other responds "121." The first one writes down "121". Both have omitted the units, but the units are still there, merely assumed. Later, when their boss reads the note left on a nearby work bench, he says to someone nearby "That's great that we got it up to 121 kilowatts today."
For your specific use case, $36\ \mathrm{m\,s^{-1}}\ \hat{u}$, insisting that the magnitude of the velocity is merely 36 and is unit-less would be false. In fact, that does not even make any sense. In fact, this does not even need to be a math or physics question - it is basic English language. A vector is magnitude and direction, and 'm/s' is part of the magnitude.
If you come to me with a formal report in a formal setting that suggests the speed of a velocity is 36, then that report is utterly useless to everyone. I could ask you "Did you measure it in banana-lengths per millennium?" In fact, the report (again, assuming it is completely formal) is in fact complete gibberish and not something that anybody can use for anything. In fact, the report would probably be trashed and you would be asked to write a new one... or at least fix the current one.


How much better would blender be if I upgraded my Ram?

Question: I currently use AMD A6 5200 APU processor, with linux (Zorin OS 15) as operating system. I have 4 GB of ram. I can run blender 2.92 at a good speed however it does slow down when I have over 4000 particles during scenes or complex node groups but I can get around that, however what I can't get around is animation playback in viewport. It gets really slow sometimes with around 2 armatures in scenes even with less complicated animation. All I need is around 24 fps of viewport animation playback.How much better performance can I get if I upgrade to 8 gb of ram (because this is only something I would be able to afford right now so I would like to use my money wisely)
Comment: Generally having more RAM helps improve your performance. But one can't tell when you say you need 24 fps viewport playback if 8 GB will ensure that. Because it all depends on what exactly you are doing. "Less complicated animation" sounds very subjective. Maybe the 2 armatures are simply animated, but what about the rest of the scene? How much geometry is involved? What else is going on there? And do you want 24 fps playback in solid view or rendered view? The viewport playback speed depends on many things.
Answer: Use a System Monitor or Task Manager tool or similar (eg, 'top' on Linux) to see if your system is using all of its memory when you're doing a large, slow operation. If you still have free memory then that isn't the bottleneck. If, however, the memory runs out and the system starts swapping to disk (known as "page faults" or "virtual memory swapping") then you would benefit from adding more memory.
Comment: @JachymMichal RAM is still a requirement regardless of the amount of GPU memory - depending on the complexity of the scene. Adding more main memory will only make things quicker if swapping was causing a bottleneck. I believe if you don't have enough GPU memory then it will simply fail to render rather than slowing down.
Comment: Thanks for replying :). I generally render with Cycles on CPU so my experience with Eevee performance is limited.
Comment: Hey :). How is this handled when using Eevee in viewport? Is RAM still important, or does GPU memory come into play?
Answer: More RAM is generally-speaking better at the 4 GB level; but another thing you should seriously take into account is RAM speed. I have a local rendering machine which has an old (but surprisingly reliable) MSI 760GM-P34 motherboard; which has a cap of 16 GB. I've got all 16 GB now, but it also started out with only 8 GB. The significant improvement came when I threw out the 8 GB stick--which was 1066 MHz--and replaced it with a 1600 MHz stick. Everything is much smoother now.
This is generally true for any software which alters memory on a regular basis, Blender is certainly included whether you're using a CPU or GPU; especially when you're working with physics or particle systems and doing a lot of baking. I suggest you look at the available speeds for your motherboard, check on what you're using now, and consider shifting it up to the fastest available.
Answer: If you use GPU rendering it is not that important, but more RAM is always better if a programm can use it. If you use CPU rendering it will be better to have more RAM.
Answer: If you add more ram both the GPU and CPU will benefit (as you have an APU in your system)
The APU uses system memory for graphical processing and you would notice a great improvement within games and video editing programs, therefore any large scenes in blender that is eating your ram currently would benefit.
The main bottleneck itself (if system memory is not the issue) would be the CPU itself, While AMD APU's are great for the price, there are upgrades you could make to your machine for better results, such as a new CPU, dedicated graphics card, SSD etc, but this is all costly but worth considering in the future if you continue to use blender or even decide to use it to make money.
A recommendation would be to aim for 8-16gb of memory to get the most out of of your system.
this is all based on personal experience with an old APU and gaming/photoshop, a small improvement was there after upgrading from 4gb to 16gb but decided on a total rebuild to achieve much better results.
Answer: Generally you want more than 4 GB of RAM for most jobs, CPU rendering is not too intensive on RAM compared to GPU rendering (in GPU rendering you want bigger tile sizes so its faster). However when doing real-time rendering you probably want at least 8GB of ram.


Collapsing Content in Fluid, Responsive Design

Question: I have a responsive design, which I'm relatively new to, that has a series of fluid images in the primary content area. Below 800px this content area has a large image, that spans its full width, followed by columns of 2 images after that:
<code>body.our_work #work ul {
    list-style: none;
    margin: 0%;
    padding: 0%; }

    body.our_work #work ul li {
        float: left;
        margin: 0% 1.075268817204% 1.075268817204% 0%; /* 10/930 */
        position: relative; }

        body.our_work #work ul li.small {
            width: 49.462365591398%; /* 460/930 */ }

            body.our_work #work > ul > li:nth-child(odd) {
                margin-right: 0%; }
</code>
At and above 800px, the content area turns into a first row of one large image and one small image, followed by rows of 3 images across:
<code>@media screen and (min-width: 800px) {

    /* Convert to 3 Columns */
    body.our_work #work ul li {
        margin: 0% 1.075268817204% 1.075268817204% 0%; /* 10/930 */ }

        body.our_work #work > ul > li:nth-child(odd) {
            margin-right: 1.075268817204%; }

        body.our_work #work ul li.large {
            width: 66.129032258065%; /* 615/930 */ }

        body.our_work #work ul li.small {
            width: 32.616487455197%; /* 303.3333333333333/930 */ }

        body.our_work #work ul li.large + li.small {
            margin-right: 0% !important;
            width: 32.795698924731%; /* 305/930 */ }

        body.our_work #work > ul > li:nth-child(5) {
            margin-right: 0% !important; }
}
</code>
For some reason, about 20-30% of the time this content area will "collapse" such that it and the containing images are only a portion of the full width of this column. The structure (i.e. 1 large and 1 small image in row one and 3 images in all subsequent) is correct, however.
I think this has something to do with the fact that when the browser's painting the page it doesn't know how large the content area is because the images are fluid.
To complicate things, inspecting the HTML in Chrome or Safari or just clicking the content often causes the content area to expand to its expected size. So... it's a little hard to see what's exactly happening. Further, resizing the window, sometimes even just a little bit, corrects the sizing.
Note that I don't encounter the issue on iPhone, iPad, or Kindle Fire.
Any help is greatly appreciated.
jsFiddle: http://jsfiddle.net/p8n9W/
Update 1:
- I can't seem to repeat in Firefox.
- The layout is a fixed sidebar with a fluid second column.
- When the issue does occur, the width of the content area seems to end up being the width of the heading "Our Work".
Answer: Turns out the issue was that the fluid column in a 1 column fixed 1 column fluid layout can't be floated. Floating it left caused the column to collapse when certain content was contained within.


I've reinstalled Xubuntu with old usr .. apt-get problems

Question: I was facing a lot of grub problems which couldn't be solved otherwise, and hence reinstalled. But to keep my old software, I did not format the usr n opt for which I've separate directories. Afterwards, I mounted them in their positions and edited/etc/fstab to get back my previous state .. of course I had to install mono again, since I guess it's stored in bin, lib, et al, rather than usr/bin, usr/lib, et al .. every software is working perfectly as expected. However, I had no idea that the dpkg stuff aren't stored in usr. (/var, /etc was & is in the same partition as / )
Hence, I can't upgrade my kernel or other stuff .. is there any way to make apt-get check all the software in usr and update it's lists, and maybe correct the dependencies of they are available under the repos in /etc/.../sources.list?
Of course, I must add the required ppas, and reinstall stuff outside usr, such as some compilers.
Furthermore, just a suggestion in the wrong place I believe, can't there be 2 or more extra lists, in usr & under /, which store the names of the packages installed under it, and cross location (in or out of usr) dependencies, so that apt-get accesses them such that in case someone does something like what I did, apt searches the list and updates it's main list?
Answer: seems like you messed up your installation with the reinstall, there are complicated methods to fix this, and yet you might end up with a broken installation, which would be very susceptible to future version upgrades,
i won't advice that, given that i tried them a while back and its kind of more work than output, hence keeping usr or other dirs from old installations in not very "cool" so as to say, for reinstalation i now maintain a script of all the stuff(pkgs and repos) i need in a script file and run that after a reinstall, i only catch being you need to have an unlimited(so as to say) data connection.
the simple redundant process would be a complete re-installation, for the grub related problems i'd advice you to get to know grub installations or in case of a dual booting sytem use grub4dos which is much simpler, from a usb live system or checkout the gui distro http://sourceforge.net/p/boot-repair-cd/home/Home/ or boot-repair in general,


~/.ec2/id_rsa-gsg-keypair not accessible: No such file or directory

Question: I'm trying to launch a Hadoop cluster on Amazon ec2, using the instructions in "Hadoop in Action" (also here: http://wiki.apache.org/hadoop/AmazonEC2).
I've set up my private ssh key and configurations, but when I try to launch a cluster using the command-line tools:
hadoop-ec2 launch-cluster test-cluster 2

I repeatedly get this error:
Warning: Identity file ~/.ec2/id_rsa-gsg-keypair not accessible: No such file or directory.
Permission denied (publickey,gssapi-with-mic).

The ~/.ec2/id_rsa-gsg-keypair definitely exists, though, and I did chmod 600 it:
> chmod 600 ~/.ec2/id_rsa-gsg-keypair

> ls -l id_rsa-gsg-keypair
-rw-------  1 my-username

Any idea what's wrong?
Answer: You may have already realized this, but the problem is possibly related to the ~/ path usage. Try using the absolute path /home/username/.ec2


Type of glue for sealing cable entries

Question: I am looking for the name of a type of glue (I think brand recommendations are not permitted, so not that) which will seal an electrical connector to the socket it is plugged into in a reversible and temporary manner. I've scraped this stuff off before and it is usually some form of yellowish translucent gum. The exact use case is sealing a USB plug to a waterproof USB solar-powered power pack (and the other end of the cable to the similarly waterproof thing I'm plugging it into), so this can be used outdoors.
Comment: Silicone caulking?
Comment: I've heard the brand name Silastic (DuPont, I think ) used for this type of non-conductive glue.
Answer: Not what you are describing, but "duct seal" is a (all I've ever seen is gray) non-hardening putty intended for plugging conduits to prevent various things (air, water, rodents, insects) from coming along with the wires, usually at building penetration points. Find it where electrical supplies are sold, though it may not be all that obvious on the shelf.
It is removable and reusable.
What you are describing sounds more like hot glue (which could work, though its performance exposed to sunlight may be dubious.)

Type of glue for sealing cable entries


How to show $n^2+m^2 = a^2+b^2 = (n-a)^2+(m-b)^2$ has no nonzero integer solutions?

Question: How do we prove that
$$n^2+m^2 = a^2+b^2 = (n-a)^2+(m-b)^2$$
has no nonzero integer solutions? I know two ways to prove this by taking a geometric interpretation but I don't want such a version. How can I prove the above by just "looking at the equations"? What is the "natural" approach.
Comment: Related: http://math.stackexchange.com/questions/105330/equilateral-triangle-with-integer-coordinates. Note that the accepted solution is purely algebraic.
Comment: @Micah, that's exactly the motivation behind this problem but I saw it elsewhere. One can use Pick's theorem or draw the smallest enclosing rectangle and either way argue to contradiction that all areas must be rational.
Comment: Hey can you please explain the geometrical interpretation approach to solve this problem?
Answer: Recall that $p^2+q^2$ is of the form $4k$ if $p,q$ are both even, of the form $4k+1$ if they are of different parities, and of the form $4k+2$ if they are both odd.
Let $(n,m,a,b)$ be a solution where $n > 0$ is minimized. As
$$n^2+m^2=(n^2+m^2)+(a^2+b^2)-[(n-a)^2+(m-b)^2]=2an+2bm \, ,$$ $n^2+m^2$ is even.

If $n^2+m^2$ is a multiple of $4$, then $n,m,a,b$ are all even, so we can obtain a solution with smaller $n$ by dividing all of them by $2$: a contradiction.
If $n^2+m^2$ is of the form $4k+2$, then $n,m,a,b$ are all odd. But then $n-a$ and $m-b$ are even, and so $(n-a)^2+(m-b)^2$ is a multiple of $4$: also a contradiction.

So there is no solution with $n>0$.
Answer: From individ's comment, $n^2+m^2$ is even, so $n$ and $m$ are both even or both odd.  So are $a$ and $b$.
If $a,b,m,n$ are all odd, then $2an+2mb$ is a multiple of 4, but $n^2+m^2$ is not.
If $n$ and $m$ are even, then $2an+2bm$ is a multiple of 4, so $a^2+b^2$ is a multiple of 4, so $a$ and $b$ are even.
Then $a,b,m,n$ are all even, so have a common factor, 2.
Divide all of $a,b,m,n$ by 2, and you get a smaller solution in integers.
So there is no smallest solution.  Hence no non-zero solution.
Answer: If this is done, it will run the next system.
$$n^2+m^2=a^2+b^2=2an+2bm$$
And it can't be.
Comment: I know you'll get this system, but I don't know why this cannot have a nonzero solution. Maybe it is simple but I haven't thought about it.


How can I paste commands on Minecraft Command Blocks?

Question: So I have a mac computer but i plugged in a windows keyboard in my mac. I am still trying to figure out how to paste commands into a command block. So how can I paste a command?
Comment: The Mac commands for copy/paste are `⌘` + `C` and `⌘` + `V`. Obviously, the Windows keyboard has no `⌘` key, but usually the windows key is mapped to `⌘`, so try `win` + `C` and `win` + `V`.
Comment: Tried `CTRL`+`V`? I'd guess that you're posting here because that's not working, but just making sure.
Comment: Ok and I did try CTRL+V so I will try win+c and win+v
Answer: This actually depends on what version you're using. Since there's no right-click function in the command block menu, you have to use keyboard shortcuts; however, different versions use different shortcuts. Minecraft 1.7.10 and earlier were all made using the shortcuts for Windows and other systems, so if you're using one of those older versions you have to use Ctrl+V to paste. This gets confusing, because other applications still use ⌘ on Mac. However, if you're using any version of 1.8 or later, you can use ⌘ + V, like the other applications on Mac do.
TL;DR ⌘ + V if you're using 1.8 or higher, Ctrl+V if you're on 1.7.10 or lower
Answer: All you need to do is use ⌘+C after highlighting the command you want to use to copy it, and then go into the command block and use ⌘+V to paste it.
Comment: Do you think you could improve your formatting? (Such as using the  tags?)


Neutrality in Bitcoin Verification

Question: Is there any build-in mechanism to retain neutrality in the verification process for bitcoin miners? I am thinking of a situation where I offer miners a fee not to include transactions from a certain wallet in their blocks to slow down/ fully prevent settlement of certain trades (not that I have a specific use-case in mind, it is more something I consider an interesting game in terms of setting the right incentives for miners).
Comment: All miners mine blocks. If one miner does not mine some transaction other will. How can you offer a fee to all of them?
Comment: Well, as I said, it is more a thought experiment: Assume I can generate of some kind of trust regarding my actions. If I want to prevent bitcoin outflow from a certain wallet I can monitor if a transaction initiated from that wallet is awaiting to become part of the new block. I could offer to pay a fee if specific transaction is NOT included in the next block.
Comment: So, you're trying to delay/censor a third party's payment? AFAIK, there's no built-in support in Bitcoin for that…
Comment: You should be a bit more specific of what would be the way of attack, as you cannot bribe a significant portion of miners. And each of them has the interest in mining that block to get a fee, so you would have to bribe majority of them.
Answer: No, there is no such mechanism. Bitcoin leaves each miner entirely free to decide how to include valid transactions in the blocks they mine however they choose.
With less than 51% of mining power conspiring, at worst they could make transactions take about twice as long. With more than 51% of mining power conspiring, bitcoin loses a lot of its desirable properties.
A lot of things prevent this in practice though. For one thing, if there was evidence that 51% of mining power was actually conspiring to censor or blackmail, the users could get together and change the proof of work algorithm, rendering everyone's mining hardware useless. This is kind of the nuclear option for the users because it will also cost honest miners a lot of money and without honest miners, bitcoin is not useful or secure. Miners know that users have this nuclear option, so they're very unlikely to conspire in such an obvious way.

Neutrality in Bitcoin Verification


Who is a tester in an Agile Team?

Question: In an Agile world, would you consider all of the team members testers? Are they part of defining the quality of the software? How can a team member be a good agile tester in your mind? What are the qualities you are looking for a tester in an Agile world?
Comment: Agile is such a cliche term that encompasses quite a large spectrum of varying methodologies. All of the agile teams I have worked on has had dedicated QA resources (some whom also performed development tasks, some that did not). To get a better answer for this question could you please describe the agile methodology that you're inquiring about.
Answer: If your question is "Who is a tester" my answer will be "anyone who does tests".
But if you are asking who should be a tester, it will depend on the team resources, abilities and strategies.

When team members have different abilities, maybe the easier option is assigning someone the tester role and making him/her accountable for test assets.
On the other hand, homogeneous teams can have a rotating tester role. The main benefit of having a different person creating tests for each sprint is that everyone on the team will become aware of testing activities and when they return to the developer role they will make their code more robust and testable.
Another option for homogeneous teams is not having a tester role, but allocating a 15-20% of everyone's time to testing activities. Similar benefits, but it is important to decide who is going to test what. It's preferable not to test each one's own code to get more defects detected sooner, because we usually become blind to our own errors.
Finally, big projects with many scrum teams often create a cross-wise team dedicated only to QA and integration activities.
Comment: I like the idea of the rotation for the tester. Have you tried that? or have you been part of a team that done that?
Comment: No, I haven't. If I had to do that, I would begin having some pair testing sessions in order to get everyone aligned.
Answer: Agile teams are cross-functional teams. They estimate their work from design to delivery often on a story based level. This includes the testing work, since testing should be part of the definition of done. One of the most popular Agile frameworks Scrum has no dedicated testing role. Everyone is named member of the Development team.
From the Scrum guide:

Individual Development Team members may have specialized skills and
  areas of focus, but accountability belongs to the Development Team as
  a whole.

Now I think anyone in the team should be able to execute the test the work. Keep in mind Agile is not mini waterfall where all the testing is postponed until the end, executed by a certain discipline. Keep in mind a lot of team functions like this. Still do not postpone testing until the end.
Having someone with a QA background in the team is a great plus, now this person can share his knowledge with the rest of the team and get everyone on a high quality level. If not the whole team is up to the task at this moment, try some pair testing until they are.
Qualities to look for are:

Team player
At-least basic programming
Test automation knowledge
Passion for quality
User centric view (instead of technical)
and of-course experience with testing software.

Maybe read following book: http://agiletester.ca/
Answer: In Agile, both the development & testing tasks are done collaboratively, but there is an exclusive tester for exhaustive testing sake.
The exclusive tester can also involve in development which is called pair programming.
The developer writes the tests which is called unit testing.
Hence except from product owner and scrum master everyone are termed as Developers.
Comment: When you are talking about "exhaustive tasking sake" what are you talking about? Can't those be shared with the developers?
Comment: Most of the user stories require exhaustive testing. As 100 percent  test automation for a user story is idle scenario, only the important and reusable test cases are taken for automation and a exhaustive manual testing would be performed. yes, the testcases can be shared.

Who is a tester in an Agile Team?


Do higher resolution laptop displays matter for programmers?

Question: I'm buying a new laptop that I'll be using mainly for programming.  A couple of options that really intrigue me are the Asus Zenbook UX31A and the new Retina Macbook Pro.  It's obvious that the high-resolution displays on these laptops is useful for entertainment, photo-editing, and other things.  My question is this:  Do these displays provide any benefit for programmers?  Do these displays make code any easier to read?  Are they any easier on the eyes after a whole day of staring at the screen?
Comment: Do keep in mind that the Retina Display by default does not give you an effective resolution of 2880x1800. It scales non Retina apps, and keeps Retina apps the same. So your effective resolution is 1440x900. There are third-party apps you can download to change this or use the scaling feature in the display to get a 1900x1200 resolution. But I've found that anything more than 1680x1050 is almost unreadable on a 15" screen.
Comment: Those two laptops are not really comparable.  The Asus has an ordinary 1080P display, while the other laptop has a Retina display (I'm guessing about four times as many pixels).  That said, unless you do detailed graphical design, I'm not sure that much more graphical horsepower is worth it if you're just writing code.  A 1080P display produces pretty sharp 10-point characters.  The amount of available screen real-estate is a more important factor; a larger screen than 15" might justify more pixels.
Comment: Screen real-estate makes a *huge* difference; pixel density not so much.
Comment: Quick answer is 100% no
Comment: I suggest you read the answers I got on apple.stackexchange.com just yesterday  http://apple.stackexchange.com/questions/54905/retina-macbook-pro-fonts-look-terrible
Comment: @Shauna: yes, you're correct, but I wanted to underline that DPI-awerness is not thanks to X server but an effect of interaction between toolkit (Qt, GTK) and how it's used/configured (usually by the desktop environment).
Comment: @RobertHarvey - Well, you can compare the resolutions.  They're much higher than others.  Plus, the pixel density is pretty close (especially compared to other laptops).  http://www.theverge.com/2012/6/11/3077659/retina-display-macbook-pro-comparison-statistics
Comment: I tried different resolutions. Word and Acrobat both looked terrible no matter how I set it. I didn't try any third party apps of course. Could you respond to my question on the apple stack exchange with this info?
Comment: high res monitor is good for browsing pictures + diagrams (such as UML ).
Comment: @AndrewFinnell in Display settings you can change the effective DPI of applications, so you're not constrained to effective 1440x900 even with stock OSX. And yes it is worth it, every OS (Win, OSX, KDE, Gnome) are more-or-less resolution independent. If the text is unreadable because it's too small just increase the DPI. It's quite irritating seeing people assume that 96dpi is the One True DPI™.
Comment: @HubertKario - Pedantic nitpick - Gnome and KDE aren't OSes, they're desktop environments, which run on Linux OSes such as Ubuntu and Fedora.
Comment: Possibly related (especially if you use Linux): [Ask Slashdot: Good Linux Desktop Environment For Hi-Def/Retina Displays?](http://apple.slashdot.org/story/12/11/30/2010203/ask-slashdot-good-linux-desktop-environment-for-hi-defretina-displays)
Comment: They do not matter (unless you are writing graphical software): your shell and vim / emacs windows look good enough on a normal laptop.
Answer: The benefit to a higher resolution is the ability to fit more on a screen. This may or may not be useful to you as a programmer. Having more lines of code can help you grasp some things better, other times its just more clutter. As for eye strain that depends on what color schemes, brightness, contrast, lighting, test size, refresh rates... Text size is really the only thing that resolution affects and even that is adjustable outside of resolution.
Comment: The real benefits of a high res display isn't that you can fit more (even though, obviously, you can). It's that at a given point size, the text will be _much_ more legible on the high res display. So, if I already can fit as much text as I want, going to a higher res means everything is easier to read.
Answer: I'm typing this on a Retina MacBook Pro. The biggest improvement of the high-res screen isn't the available real estate but the greatly improved sharpness and clarity of on-screen text. It looks like print. Programming is one of the activities that benefits most from better looking text.
Comment: I agree. The MacBook Pro Retina actually reduces eye stress, and with all the staring at text that programmers do, the Retina display makes programming so much easier on your eyes.
Answer: tl;dr = yes; code readability decreases sharply with resolution, and I see no reason why making bugs literally harder to see wouldn't result in...making bugs harder to see.
The stats have it. Reading speed is increased by up to 25% on displays of 300dpi (as opposed to the average resolution of PC desktop monitors.) Or so says usability guru Jakob Nielsen, at least. Comprehension is also up sharply, IIRC.
http://www.useit.com/alertbox/web-typography.html is a little OT, but provides excellent context for the somewhat older guidelines at http://www.useit.com/alertbox/9703b.html.
I can already hear gruff geeks trying out some tough-guy line about how real coders have so much screentime behind them that they can read code at any resolution. But of course they can't prove it, because they've never benchmarked their own brains. They just have gut-intuition that they read pretty good on a computer, perhaps better than most, and that it comes with the territory. So file this one under other flights of hypermasculinity and cultural egocentrism. (How do you suppose resolution affects a non-native reader of English? How do you suppose that the industry is affected by restricting the supply of coders to those with unusually precise eyesight?)
Yes, resolution matters -- a lot -- and yes, Apple is slaughtering everyone else as usual, because no one else seems to consider the 'U' in UX. Go buy that Retina MBP. I might bump into you in line.
Comment: one of the few answers "on topic" (not talking about "having more windows open in the bigger amount of pixels").
Answer: Resolution does matter for development even on a laptop. Try to run Eclipse with the Package explorer open and a source file with the MacBook Pro 13". It is not fun. IDE's are not meant to run on low resolution displays. If you are used to vi and tabing around I imagine a low resolution display will work just fine.
The next important thing is to make sure all the text is very clear. Nothing worse than a high resolution on a small screen where you cannot read the source code.
Use SetResX to change the Retina Display to effective 2880x1800, it's not worth killing your eyes over. But the default 1440x900 or even the resolution above that gives nice results.
Also based on what I read about the Asus notebook the MBP beats it hands down in every way. So you are really talking about money here. If you are willing to spend the $2400-$3000 ish get the MBP. If you have to stick with something less than $2k your option is only Asus. If you want the most performant machine the MBP Retina Display has fantastic hardware in it.
Comment: Forget about resolution; if you're trying to do development in an IDE on a 13" screen, there's your problem right there.
Comment: @MasonWheeler: Yep.  One of our architects replaced his desktop box and 19" monitor with a 15" laptop and after a week was complaining about neck pain.  Turns out he was hunching over his desk to see the smaller screen.  If I had to work on a laptop for more than an hour, I think I'd crank the resolution *down*, dump the IDE and go back to vi.  Productivity loss would be about the same either way, and I wouldn't have a headache when I was done.
Comment: Can you confirm that with SetResX, that text looks good on Eclipse? What other tools have you tried?
Comment: @MasonWheeler touché
Comment: @KyleHodgson The text in Chrome looks better at 2880x1800 because it isn't scaling it but its pretty much unusable because of how small everything is. Eclipse appears to be using the DPI routines in the SWT layer as the text looks fine at any resolution. Either that or I'm very tolerate with how text looks. MS Word document text looks bad. But surprisingly MS Outlook looks pitch perfect.
Comment: @AndrewFinnell interesting! So some things have been worked on already. Glad to hear that. I'm going to have to see if I can get RubyMine, Coda or TextMate downloaded and installed this weekend before one of the Genius Bar people runs me off!
Comment: @TMN I would get a 23-27 inch external monitor and use the laptop screen as an extra screen. I would the external screen mainly, and the laptop screen for additional stuff.
Answer: Generally speaking, increased visual real-estate is a good thing with programming.  Most modern IDEs have a number of panels that you'd like to have open and it's nice to be able to see all of that information "at once."
There is a nefarious relationship between resolution and screen size.  The easy rule of thumb is "the higher the resolution, the better" along with "the bigger the screen, the better."  The problem is when one of those elements becomes fixed.  A super high resolution on an itty bitty display will simply be unreadable or will lead to eye strain.
Many developers work with multiple monitors for the above reasons.  It's a reasonable way to balance the relationship between resolution and screen size, but still keep adding to the overall real estate.
As others have pointed out, the two systems you mention have significant differences in the display resolution.  The Mac will have more effective real estate without venturing too far into too-small-to-read territory.
Your questions:
- Yes, there is distinct benefit for programmers with larger screens and higher resolution.
- It won't make the WTF code any easier to understand, but having larger blocks of code available makes it easier to understand overall program flow.
- I don't think you'll see a noticeable difference in eye strain with the two models you mentioned.  OTOH, this answer is pretty particular to your question and not very generalizable.
My ideal setup would be two or three 24" widescreen displays for coding against.  If a laptop was my primary system, I would be happy with one or two 24" widescreens to supplement the laptop display.
Answer: Yes resolution makes a big difference, in that you have crisper text.  Just open up terminal on a retina macbook, turn the font size down and see how easy it still is to read it.
Now if you are using colorful IDE color schemes in anything from VIM to XCode it also makes a big difference.  Fonts are smoothed on most LCD screens using subpixel rendering which takes advantage of the red, green and blue bars in a common LCD pixel, using them as partial pixels, and then compensating for perception of colors at the edge to produce much "clearer" text.  This works really well with black and white text, but much less with colored text, especially at low point sizes.  As a result a low-res laptop displaying a lot of code in a smallish (9-10px) size, looks pretty bad.  Retina displays effectively double the font size and half the screen size (on each dimension) reducing the effects of sub-pixel rendering on color text.
Also, refuting another post, the inverse square law does exactly not apply here - we perceive (size and hence) detail in any given dimension linearly related to our distance from it - this is why we can measure things in minutes of arc/angle in astronomy and marksmanship ( http://en.wikipedia.org/wiki/Minute_of_arc ).  The other post does not actually claim other wise, but may imply that doubling the distance from an object Quaters its clarity, when really its half.
Megapixels in a display, scale in both dimensions (so does cost!) but we can safely consider detail in terms of distance and/or resolution by looking at single dimension proportions.  That makes the retina displays about doubly clear, though maybe 4 times more expensive.
Answer: Yes, the screen resulution is extremally important thing for programmer. While the quality of the colours is the most important for web developers (for SQL programmers etc. it's a minor issue), everyone will benefit from high resolution.
I'm actually working on laptop with screen resolution 1366x768 and it's a big mistake to buy something like that for the programmer. It's hard to work with Eclipse, because not much code fits on the screen. I need the console which is 200 characters wide and it hardly fits on the screen, the Android simulator doesn't fit at all. Fortunatelly I have external screen, but it's not very comfortable to type on laptop keyboard and look on the screen that stays on the side.
Almost everyone I know uses 2 displays when it is possible, and some use even 3. Generally, they are using the biggest display available, 24'' with full HD. Such resolution makes sense, because you can fit more things on screen - and one use a lot of them - IDE, a few consoles, web browser, skype etc. - and what is worse, everything should be visible at once.
So, if you want to make your developers more productive, don't buy the laptop with low resolution, please!
Comment: Get an external keyboard and mouse.
Answer: The higher resolution isn't likely to be particularly useful to you on a notebook.  The reason high-res displays look better on tablets is because you tend to hold them a lot closer to your face than a notebook.  By the inverse-square law, if you hold something flat twice as close, you see twice as much detail in both the X and Y dimensions.
So having a notebook without an ultra-high resolution display, and keeping it at a normal distance from your eyes, will give you the same experience as an ultra-high resolution tablet display held much closer.  Any claims to the contrary (see: MacBook with Retina display) are just marketing hype, and as Kyle pointed out, tend to actually look worse unless they're designed specifically with the ultra-high resolution display in mind.
Comment: they look good because they're using higher DPI setting to draw fonts and icons, not because your holding them much closer
Comment: @Hubert: Yeah, that's what they say in their advertising.  Basic physics, though, says otherwise.
Comment: What basic physics say otherwise?! You have more pixels that take the same amount of physical space. You draw stuff assuming the same physical space (before the letters were supposed to be 3mm in height on screen, now they have to be *too* 3mm in height). If you're using a toolkit (Qt, GTK) that is DPI aware and the OS reports correct DPI for the screen, the whole application will look good. Not Apple's fault that programmers use shit toolkits to make their applications.
Comment: Oh, and for their marketing claims, if you assume 20/20 vision, then iPhone's 5 326ppi at 10 inches, iPad's 3 264ppi at 15 inches and MBP with Retina's 220ppi at 20 inches is above your retina resolution.


Are there standard example research papers for teaching methodology and experiments?

Question: Are there recommended or standard published papers (not books) that show great research methodology/ scientific methods?  I am trying to help out a friend who is in business and they are trying to study aspects of humans (in terms of their clients).  I gave him the book The Craft of Research, but it's long and I wonder if there is a paper that could do the same job.  Basically I want to show him a good example of coming up with a hypothesis, accounting for variables (such as stating that something was done in order to eliminate a problem), and analyzing the results.
Comment: If he is in business and he can't even finish The Craft of Research, I'd rather suggest him budget some consultant money to hire someone (maybe you?) to work with him through the process. Learning and immediately applying research hastily would likely waste time and resources. It's correct that some papers may introduce some 101s about research design and analysis, but papers tend to be concise and use citation extensively; he may still end up needing to reference other publications and articles.
Comment: I know you didn't ask for books, but my answer may be helpful to you (and others). My PhD methodology is Design Science.  An excellent academic scholarly book, is "Design Science Methodology", by Wieringa, Springer, 2014.  There are about 100 references, in the book.  So you can learn from the book, and then find the relevance published papers that you are looking for.
Answer: Qulatrics has a nice concise (and free) guide to doing marketing research. Not a journal article, but I give it to my students in my research methods course because it's practical and comprehensive but not overwhelming. In fact, they have a lot of useful resources here: http://www.qualtrics.com/university/researchsuite/research-resources/other-resources/ebook-downloads/
Answer: I personally find a lot of both elegance and accessibility in the descriptions of well-done infant and animal cognition studies.  A nice source for examples is the Harvard Laboratory for Developmental Studies, and a nice short accessible piece from their library is this one: "Chicks, like children, spontaneously reorient by three-dimensional environmental geometry, not by image matching": it's only 3 pages long, presents the hypothesis, method, and results quite tersely, and the experimental apparatus can be built with common household objects.


Help with the problem of conditional probability

Question: Two friends are students of the subject of Statistics so that when one passes the notes lack other. It is known that the first will attend 80% of classes and the second at 40%, independently. What is the probability that the friends have all class notes?
Comment: How many classes?
Answer: For any particular class, let $A'$ be the event "Alicia did not attend," and $B'$ be the event "Beti  did not attend." The probability of $A'$ is $0.2$, and the probability of $B'$ is $0.6$. Thus by independence the probability neither showed up is $0.12$.
It follows that with probability $0.88$ at least one showed up, so they have the notes for that class.
If there are $n$ classes, the probability they have all the notes is $(0.88)^n$.  Here we are assuming that attending the various classes are independent events. This is probably not a reasonable assumption.
Remark: Or else let $A$ be the even Alicia attended, and $B$ be the event Beti did. Then $\Pr(A\cap B)=0.32$. Now use the formula $\Pr(A\cup B)=\Pr(A)+\Pr(B)-\Pr(A\cap B)$ to conclude that $\Pr(A\cup B)=0.88$. So the probability one or both attended is $0.88$.
Comment: Thanks Andre, Thanks Andre, I understand the approach and solution. I'm settled now another problem relaconado the same issue.
http://math.stackexchange.com/questions/446376/help-with-the-conditional-probability-in-this-problem
I look forward to your help, thank you very much in advance


making a custom installable theme package

Question: I have completed developing my custom theme in magento and now I want to make it installable or I want to package my design like other magento themes so that I can just put it in htdocs and go through the installation steps to install that custom theme. Can any body provide me a clue on how to make the custom theme installable?
Comment: Do you have any example of this?
Answer: Im pretty sure this is what you are looking. Themes are packed just like extensions to be installed with Magento Connect.
The link i posted is the official guide to pack extensions and themes in Magento.


How to talk about "vision problems " and "eye glasses "?

Question: How can we ask a person if one has a vision problems? and what is the other name for "eye glasses?
Answer: It depends on the context, but informally you can ask

How's your vision?

or

How are your eyes?

I'm not sure about other countries, but in the US "good" vision is called "20/20".  So you can ask:

Do you have 20/20 vision?

"Eyeglasses" are called that, or just "glasses".  So you can ask:

Do you wear glasses?

A more formal way to ask this (such as on an insurance form) would be:

Do you wear corrective lenses?
Comment: Many thanks. I hv also heard the word "power " while talking about vision n glasses. Any comments on it?
Comment: @AltafJahangir  There are a number of optometrist terms related to glasses which you would probably know well if you wear them (which I don't).  "Diopter" refers to the *refractive power* of the lenses, but you can sometimes use "power" to refer to the magnification of reading glasses (1.5x, 2x, 3x, etc.)
Answer: What is your vision?
Also you can ask the following questions instead.

How strong are your glasses?
What is the power of your glasses?
What is the strength of your glasses?
Comment: "What is your vision?" would be a good question if you are asking someone about their exact vision (e.g., "My vision is 20/20.") However, that is not what the OP asked.


How do you obtain orchestral/instrumental parts for individual songs from a musical theatre show?

Question: Looking to purchase instrumental or orchestral parts to individual songs from many different musicals in order to perform them in a concert.  All I can find is piano parts written for piano/vocal performances.
Comment: Will you be performing these songs in public? If so there are [other considerations](https://support.easysong.com/hc/en-us/articles/360047682433-What-Is-a-Public-Performance-License-) and costs besides just purchasing the parts.
Comment: I'm not here to discuss all of that.  We have already taken care of rights and licenses to perform.  I'm asking for how to find the orchestral songs of individual songs within a musical.
Comment: Why was this closed exactly? This does not seem to fall into "transcribing or finding a *particular* song" but is easy more general than that.
Comment: Full orchestrations are readily available - at ~£60 per song. But what instruments are you going to use.
Comment: It depends on the song.  We will perform 28 songs from about 15 different musicals.  I wanted to have a small orchestra play along for the songs, maybe 5-9 people (violin, cello, bass, percussion, woodwind, maybe a brass instrument, like trumpet, and probably guitar).
Comment: @Tom Agreed. Closing at a business question, maybe, but I don't think this is included in the spirit of the "transcribing / finding" reason, especially since it isn't for a specific song.
Answer: They either must be rented from the agency responsible for maintaining them, or custom arrangements must be created.
Comment: I have not been able to find any information on renting a single song from a musical.  We are not performing a full musical; just individual songs from many different musicals.
Comment: @HHart You would have to speak directly to the agency that controls the score for each musical and ask. If they don't have a mechanism for performing an individual song, then you would have to go the route of arranging your own version.
Answer: Unless the music theatre show is VERY old it falls under copyright protection. This means that most likely a publisher or another entity holds the publishing and performance rights. You'd need to get into contact with this entity. But quite often such entities do not in fact sell the performance material, but only rent it out for performances. Of course this is not necessarily bad, as it is considerably cheaper to rent the material than it would be to buy it.
Comment: This is one of the primary advantages of the Gilbert and Sullivan musicals.
Comment: We have already applied for and secured all rights and licenses to perform each song.  I am now searching for orchestral parts for these songs, which are not published by the same organizations or names who hold the copyrights.
Answer: I feel like most of the parts I've read from in professional orchestras have been stamped with "Luck's Music Library," a vast and long-standing clearinghouse for renting and purchasing orchestral parts. For instance, you can rent Gershwin's "I Got Rhythm" for $90 or a medley of selections from Annie for $130. Note, you have no guarantee of finding the individual song free-standing—the Annie medley was all I could find when I went looking for "Tomorrow"—but the more popular the song the better the chance.
Answer: Can you name the piece? If so, there are three solutions:

Arrangement: someone already did an arrangement, might as well search for *.mid files, where you can extract the score, although it might have sub-par quality.
There are sheet music vendors with a procurement service.
You can as well search specifically for the score. Try google searches with parameter "filetype:pdf", for example "score [name of song/musical] filetype:pdf"
Comment: There are 28 songs in our concert, from about 15 different musicals.
Answer: Orchs are readily available for downloading/printing. As an example, I've just googled Blue Bossa orchs and lots of youtube performances come up, some with a link to a publishers - $45. There are als dedicated sheet music sites which will sell orchs, in whatever key you specify, for whatever instruments you desire. Rarely for free...
Answer: You can find a lot of sheet music for orchestras and bands on jwpeper.com along with audio samples. They have a lot of arrangements and original sheet music from many genres and artists.


Effects of the Himalaya's absence on the Mongolian plateau

Question: According to the world's map, the Mongolian plateau is almost entirely covered by a desert and I just have discovered that it is north of the Xinjiang deserts, the Tibetan plateau and the even higher Himalayas, which is where monsoon winds stop by due to the elevation. I am asking if removing the Himalayas would be sufficient in order to make most of the desert (including Xinjiang's) fertile enough to support a large population and if a similar process could make central Asia more fertile as well.
Comment: If only there was a large continent with broad flat plains that weren't separated by mountains from its rainy coast. Maybe somewhere in the northern hemisphere...
Answer: Not as much as you might think, but enough to suspend disbelief for a story
If memory serves, the Mongolian plateau is part of the Himalayas. In other words, "realistically" (which isn't really what we do here, but just to point it out), you can't remove the mountains without removing the plateau.
But, fantastically, if you did, you'd get more rain - but not as much as you might think. The average altitude of the plateau is 1.6 km. That's still a lot of vertical climb for storms, which begin at sea level. To give you a comparison, the U.S. Great Plains region has an average elevation of only 450 m, which happens to be close to the lowest elevation on the Mongolian Plateau (Lake Huhk at 560 m).
Consequently, I would expect that you'd see increased fertility as shown on the following map (courtesy Google, click to enlarge):

As one travels toward the central Mongolian plateau (northeast of the purple area), the land becomes less fertile. Those deserts of the high plateau would remain. Part of the problem is that bringing rain across India is a long distance to travel only to have to move uphill onto the plateau.
The only way to make the entire plateau fertile would be to lower the plateau much closer to sea level. It, and the land between it and the sea. (I'm exaggerating that a bit, rain gets over mountains, but the lower the mountains, the more rain gets past them.)
However
I believe the idea would allow me to suspend my disbelief to allow most of the Mongolian Plateau to become fertile.
If where you're going with this is a story about a massive engineering project to remove the plateau's protective mountains... Yowzah! That's a project worthy of the Chinese culture! Keep in mind that you can't just build more beaches with the removed dirt as that would have a consequence for rain as well (it's a LOT of dirt). That's assuming, of course, that I'm right in guessing your plans. I could be wrong. But, yowzah....
Comment: Yes I actually wanted to set this in the future, when the mountains are artificially removed. Well I actually am trying to find a geographic location where to put my new country, either Beringia, Australia or in this case, what corresponds to the region people once called "Tartaria" or at least Inner and Outer Manchuria, I actually am not sure which location would be the most realistic to put my it in as I want a continental climate.
Comment: Th Mongolian Plateau is *not* part of the Himalayas. It might have association with the collision that formed those mountains, but is geologically distinct.
Comment: The Mongolian Plateau was formed by crustal extension as a result of the collision with India and Asia and a subsequent uplift, but again, not part of the Himalayas.
Comment: I'd imagine that absent the Himalayas (i.e., without India smushing into Asia), much of that area would still be either Tethys Sea floor or else its northern shores. Probably not much uplift. Far enough in the future, should India retreat, the Himalayas and the associated highlands will eventually erode, ending up with old and worn down mountains like the Appalachians.
Comment: @KeithMorrison Really? Well, I'm an electrical engineer, not a geologist. What formed the Mongolian Plateau? I'll happily improve the answer.
Comment: @KeithMorrison After watching the videos on the Himalayas posted by the Swedish Academy, my impression is that the Mongolian Plateau was formed by the collision between India and Asia. And without the Himalaya mountains, the weather patterns would be radically different.
Comment: @KeithMorrison Thanks, but can you give me a detail? That sounds like the plateau and the mountain range were formed by the same tectonic action. While the plateau may not be considered part of the range, removing the tectonic action that created the mountains would also remove the plateau, or did I misunderstand you? Thanks.


Can a bow get a non-bow enchantment?

Question: Is it possible in minecraft to enchant a bow with an enchantment that was originally just for non-bows, such as looting?
Answer: Short answer: No
Long answer: No, unless you have a mod.
Comment: I like the difference between long/short.
Comment: can answers be updated because this isn't correct anymore
Comment: Even that mod doesn't give things like looting. But it still looks cool.
Comment: This answer is no longer accurate.
Answer: Yes. If you make an Enchanted Book you can add a non-bow enchantment. If you are in Creative mode, you can enchant a bow with any enchantment; if you are in Survival mode, however, you may only enchant it with Unbreaking.
Comment: Would they take effect on the arrow launched or the bow used in meleé?
Comment: I think it depends. For example, if you tried Knockback instead of Punch on a bow, it would work on melee hit. Not certain about Looting though.
Answer: Here is an easy way to do it on Creative mode, or Survival mode. (No Mod's Required)
1: You get an anvil, and in the first slot put the bow, and in the second slot put the enchanted book of looting there. Then you should have a bow enchanted with looting now. (The Image is from my Minecraft.)
Answer: I think it can happen because of glitches - I had a bow with looting 3, without any mods installed.
Comment: Did you enchant this bow, or get it from a skeleton?
Answer: Yes you can. In survival you can't but in creative you can
There are 2 methods:

Anvil
Place a bow with an enchanted book of any enchantment

Command Blocks(Or chat commands)
you can use /give command in order to get items with any enchantments(And exceed maximum level of the enchantment).
Example:
/give @p stick 1 0 {ench:[{id:0,lvl:4},{id:16,lvl:1},{id:51,lvl:2}]}
this command gives a stick with protection IV, Sharpness I, Infinity II.
(for enchantment IDs, please see the wiki for more information.)

Can a bow get a non-bow enchantment?


How to create a currency independent commodity index

Question: I'm looking for insights on a methodology to create my own bespoke index, specifically a gold index. I'd like to take the price of gold in various currencies, along with the different cross rates between these currencies, and create a kind of fundamental "price of gold" index that is invariant to the changes in the values of each currency wrt the other currencies.
Answer: Create a "currency basket" consisting of: one third of a dollar (USD 0.33), one third of a Euro (i.e. EUR 0.33) and "one third of 100 Yen" (i.e. Yen 33.33). These amounts are chosen because they are worth approximately the same at this time, and because these are the 3 main world currencies (other than 人民币).
Now calculate the price of one ounce of gold in terms of this basket. (In 2 steps: convert these currency amounts into a single currency (for ex. dollars) and then see how many times this amount is needed to buy 1 ounce of gold).
Of course if the basket is chosen differently you get a different commodity index, so there an infinite number of commodity indexes that you can choose from, depending what "basket" you choose. For example you could have a basket where the currency weights are chosen in terms of the importance of the currency in international trade, or on the share of world GDP or whatever).


Twitter API - Determining local time in PHP

Question: The twitter API provides all tweets in UTC time. You can also get the UTC offset and the "time zone" for the logged in user:
e.g.
created_at = Mon Jun 11 13:17:11 +0000 2012
utc_offset = -18000
time_zone = Eastern Time (US & Canada)
I have no problem converting the created_at time to a timestamp and then adding the utc_offset, but the utc_offset does not take daylight savings time into account. So during DST, all of my times are off by 1 hour.
The other problem is that the time_zone value that is provided by Twitter API does not match the php timezone format (http://www.php.net/manual/en/timezones.america.php).
Does anyone have an idea on how to take into account DST to display an accurate local time to the user?
I'm starting to think maybe using client side scripting to convert the UTC time is my best bet.
Answer: I think you are right. You really only have 2 options:

Manually create an array (unless someone else has already done the leg work for you somewhere..) which holds the Twitter API time_zone strings and indices and the PHP equivalent as values, or
Use a simple JavaScript to modify the standardised time string on the client end.

I know what I'd prefer.
The second answer on this post has a nice example for the javascript
Parsing Twitter API Datestamp


How to get list of movies in itunes podcast

Question: I have a link to podcast on itunes that looks like this: http://itunes.apple.com/pl/podcast/[name]/[id].
How can I get list of movies from that podcast.
I can see two ways. First is parsing html to retrieve informations. Second, much better, is using itunes api (http://www.apple.com/itunes/affiliates/resources/documentation/itunes-store-web-service-search-api.html). However i am not able to use this api, so it returns list of movies from certain podcast. Can anybody provide guidelines?
Answer: Itunes podcast is generated from rss feed. Address to this feed can be found in itunes page source. The best way is to just parse this feed and extract all needed data.


Bonferroni correction and discussion of the results

Question: In a study in which I analyze several biomarkers through logistic and linear regressions, should I discuss in the discussion of the paper the results with p <0.05 (they only have a nominal significance) that are not significant after the Bonferroni correction?
Answer: I don't think so, because Bonferroni Correction is just trying to solve this exact issue. In multiple experiments, you might possibly encounter with rare events and correcting your significance level corrects your interpretation as well. While making an experiment, we are assuming that we could have rare events with $0.05$ probability; but if we are making $100$ experiments, then probability of no rare events become $0.95^{100}$, which is very small. But, if we assume a significance level $\frac{0.05}{100}$ and find $0.9995^{0.0005} \approx 0.9512$, we see that we made nearly the same decision for a cohort of experiments. So, as a result, your cases that are still significant after adjusting the significance threshold as $\frac{\alpha}{m}$ are actually important, not the others.
Answer: This depends on the underlying scientific questions for each biomarker and how they are related. If they are of very different kinds and give different information there is no need for any correction for multiplicity. Suppose for example that you were looking at HBA1C, middle upper arm circumference and self-reported quality of life (using biomarker in a wide sense) then you would not adjust. If the biomarkers could potentially be just different ways of saying the same thing then you probably would adjust.


Different feature importance results between DNN, Random Forests and Gradient Boosted Decision Trees

Question: I've been modeling metabolite data with 3 different regressor models. I get similar results from running feature importance with Random Forest model and Gradient Boosted Decision Trees (where I used the scikit-learn built-in feature importance), but with Deep Neural Networks I get very different results (used permutation feature importance). I also ran PCA, and PCA gave me similar results to DNN! Is this normal? Could both of them be accurate still? I have quite a large amount of initial features.
Answer: Few factors that can cause such differences -

A common issue with the default RF FE approach.
It's not reliable in situations where potential predictor variables vary in their scale of measurement or their number of categories
Read

Correlated Features
 When you have correlated features,
RF Tree-based FI approach will divide the importance depending upon how the Tree used the two correlated Features
Permutation based method will assign negligible importance to both as skipping anyone will have no impact on the result

Feature Interaction
 If we have two Features with Interaction,
Tree based approach will catch the Interaction in successive splits and accordingly divide the importance into two Features
Permutation based method will assign high importance to both the Features as dip will be high when anyone is skipped(Assuming additive Interaction)
In this case, this is a question to ponder how the FI should be divided when two Features are interacting. Ideally, a third feature(e.g. X1*X2) should be created and should get all the FI.

You should try -

Identity correlated Features using respective tests e.g.Pearson, Crammers, Spearman etc.
Use Permutation approach for all cases. Sklearn has got the option

<code>#https://scikit-learn.org/stable/modules/permutation_importance.html
from sklearn.inspection import permutation_importance
r = permutation_importance(model, X_val, y_val, n_repeats=30)
</code>

Then if needed, look for any interaction effect (See suggested reading)

Suggested reading
Beware Default Random Forest Importances
Discovering-interaction-effects-in-ensemble
Chapter#7 - Feat Engg
Interpretable-ml-book
Answer: Why would you expect them to be the same?
In one hand Random Forest and Gradient boosting are two types of different ensembles. Even if their estimator is a decision tree and they both seem to measure in scikit learn impurity-based feature importance. The result will be different. Not much is my guess, but different.
For Deep Neural Networks, you are calculating a different "feature importance" metric. So it makes sense that the calculated result is different.
Sadly, feature importance is just aggregation statistics that does not tell you much about the explainability of the model.
Different feature importance in different models is completely fine, no problem with that.


Question about the Weiss variational of gravitational action and related equations of motion

Question: I was reading The Weiss Variation of the Gravitational Action by Feng and Matzner, where the authors take the variations of the gravitational action with respect to the bulk metric $g$, the induced metric $\gamma$, and the displacement $\delta x$ of the boundary. It seems that to do so one requires that $\delta \gamma_{\mu \nu} |_{\partial \mathcal{M}} \neq 0$. I have a hard time understanding the implications of such variations on the equations of motion of the theory (equation $(4.34)$). In particular, while the bulk variation gives the well known Einstein Field Equations in the vacuum, the variation with respect to the induced metric seems to give another equation,
\begin{equation}
K_{\mu \nu}-K \gamma_{\mu \nu}=0, \tag{1}
\end{equation}
where $K_{\mu \nu}$ is the extrinsic curvature and  $K$ its trace. Does this equation determine the induced metric, just like EFE determines the bulk metric? If so, why isn't the induced metric just $g_{\mu \nu}-\epsilon n_{\mu} n_\nu$? Maybe $(1)$ determines $n_\mu$, but then aren't $(1)$ and the equation of motion associated with the variation with respect to $\delta x$ redundant?
Answer: After sending an email to J. Feng, the principal author of the article I linked, it simply appeared that I've misunderstood the purpose of doing such variational. Indeed one doesn't want to find a specific equation of motion but to identify conjugated quantities to the variationals. So the LHS of equation (1) is simply the generalized momentum associated with the induced metric, and for $\delta x$ one identifies the canonical stress-energy-momentum tensor.


Windows Server more vulnerable for password extraction during shutdown?

Question: Is a Windows Server (e.g. Windows Server 2008) more vulnerable during the shutdown process compared to the Server is up and running? Does the process of shutting down Windows introduce additional vulnerabilities concerning password dumps/extractions?
Comment: More vulnerable compared to what ?
Comment: Out of curiosity why do you think so/why this question?
Comment: @Overmind I guess compared  to a normal running machine (not shutting down machine)
Comment: @Maximilian You should edit that into your question and delete the comment afterwards.
Answer: In most scenarios, no.
In the normal working fine scenario, the processes that could cause sensitive data leaks are ended before the general system processes, so there is no danger here.
In the case one such sensitive process is stuck, the OS does not end task the others before action is taken for the stuck one (in this case the well known screen with wait or end task appears).
In the case of operating system getting stuck, there can be indeed a problem depending how complete that halt is, but this should not happen on W2008, unless there's some bad hardware involved or really bad software installed (in which case the system is already compromised).
Comment: this is the correct answer


Could an intelligent alien species reproduce via pollen?

Question: Could a sapient, animal-like alien reproduce with pollen and ovules, rather than directly producing sperm and eggs?
Comment: Why not? That is, the question assumes that it is somehow inconceivable for an alien species which is reminiscent of terrestrial animals, that is, is a mobile heterotroph, to exhibit an alternation of generations reminiscent of terrestrial plants. Unless the question spells out what logical difficulties are to be addressed the only answer can be, yes, of course, it is an alien species and has an alien life history. (For people who no longer remember their middle school botany: pollen is the male gametophyte generation of land plants; the plant as usually known is the sporophyte generation.)
Comment: related https://worldbuilding.stackexchange.com/q/113527/30492
Comment: Perfectly possibly. Not *very* likely, as the main purpose of pollen is its mobility, to make up for the host's lack of mobility.
Answer: Why not
Reproduction via pollen works. There is no reason why you couldn't imagine an alien using that form of reproduction
But it's very inefficient
This mode of reproduction consumes a lot of energy because you have to disseminate an enormous quantity of pollen in order to get a small result. Moreover, if you want to use other animals to help disseminate your pollen (as trees do), you have to create an incentive in the form of flower nectar, which costs energy.
The reason why trees use this type reproduction is because they cannot move, so they cannot use a more efficient one.
Conclusion
You need a reason why your aliens would evolve that type of reproduction.

Either they cannot meet their counterparts of the other sex (or lay eggs in some place like fish do) for some reason (or it is difficult for them).
Or maybe they rapidly evolved from plants (or other lifeform unable to move) that used this method of reproduction, and have not yet evolved another method. But then they would need to have other characterestics of plants
Comment: They probably could, but that would be very different from what we call pollen. The particularity of pollen (of trees) is that it is long-distance and non-targeted
Comment: What if the aliens make fewer, larger pollen grains that only travel a short distance between the main individuals
Comment: Evolution is constrained by existing morphology and behaviour; the only reason it needs to be like that is because it was already like that. Our reproductive system replicates the original water-borne reproduction of plankton, fern spores swim even after 400 million years on land. Reproductive behavioural filters can also amplify otherwise suboptimal traits. Also conifers are wind pollinated.  Further, pollen does offer a tremendous advantage: the ability to fertilise multiple thousands of partners simultaneously and from a great distance, no moving animal can match that.
Answer: Some plants and some sea creatures like corals and sea urchins spread their gametes and let the chance take care of the reproduction.
Therefore it is in principle possible that also other creatures keep the same way of doing it. However you need a good evolutionary reason for this to happen.
A possible motivation might be that seeking a partner and mating is less favorable than blowing it in the wind: this can be maybe because of a very sparse population and/or an high risk of being eaten during the act, resulting in a more precautionary approach to reproduction.
Answer: Probably
If it evolved from a pollen wielding ancestor then it could have retained this characteristic. In fact, if a distant common ancestor had been pollen reproducing then perhaps there is an entire class of ambulatory plants which reproduce this way.
Some things to consider might be

Are they monoecious or dioecious?
Are they synchronously monoecious or consecutively monoecious?
Are they wind pollinated or animal pollinated?

Pollination has massive implications for behaviour / culture / society - not least because pollination implies distance reproduction. The above traits will heavily influence culture and behaviour.

Assuming they are dioecious then there is no concept of father as we understand it. Children never meet their genetic father and if they do they don't notice / care. The emergence of gene sequencing is the only thing which would really allow a child to identify their parent but it would have zero cultural relevance as the culture would have evolved to be sexually divergent to the extent that males and females may never meet as adults.

There is no concept of courtship, no romance, no mating displays, no physical competition for partners. Competition takes place at the microscopic level in terms of whose pollen is most effective.

Instead of partnership they might have evolved completely different pollination-specific behaviours, such as they may be compelled to climb to high points outdoors when in season if they are wind pollinators. In this case a completely different form of competition may have evolved revolving around securing the highest point.

If they reproduce in large numbers like seed plants then males may live longer than females because the reproductive burden on females is heavier (heavier than with humans, if you think growing a baby is difficult try growing 80,000 of them at once). Child mortality rate would also be extremely high and children may not begin to have value until they are a certain age. Killing children might not be illegal.

If they are consecutively monoecious wind pollinators then they may have an aggressive climbing "male" phase where they fight over the summit of the nearest hill and a child bearing "female" phase where they stay out of danger and eat a lot.
Answer: Many animals essentially do reproduce this way.  That is, one or both parents release gametes into the environment, and fertilisation takes place externally.  It generally happens underwater (I'm not aware of any land-based animal with airborne sperm), and the parents are usually not very far from each other, but it would obviously be physically possible.
If individuals of a species are able to meet in person, then it is much more  evolutionarily favorable for them to exchange gametes directly, because (a) it is more efficient and (b) it allows for mate selection.  Even if trees learned to walk around, then you would expect them to almost immediately evolve to only release pollen when they are right next to another tree.  So, barring some extremely contrived condition, I'd expect that these aliens release pollen because, for whatever reason, they never actually meet other individuals of their species.
That raises the question of how they could have a civilisation.  I'm pretty sure there have been questions here before about how sentience might evolve in a species that never knows its parents, but this is more specific, because not only do these aliens not know their parents, they never know anyone at all.
The obvious suggestion would be that they can encode their experiences in their genome, and are born with their parents' memories.  Another possibility is that they are separated by time rather than distance – perhaps fertilised eggs lay dormant until a rare warm season occurs, and when the individual hatches it finds some kind of library left by its long-dead ancestors (although how would it learn to read?).
Or a simpler answer, which the question doesn't rule out, is that these are sessile animals, like sea anemones.  They might be able to talk to their neighbors 30 centimeters away, but simply unable to move (like the Skroderiders in Vernor Vinge's A Fire Upon the Deep).  Possibly they are also able to use pollen for long-distance communication as well as reproduction.


What are some good general strategies to get past the moon levels in Revenge of the Titans?

Question: I can't get further than the moon levels in Revenge of the Titans.  I don't seem to be able to end each game with enough money to purchase more than the basic weapons and upgrades.  Does anybody have any good general strategies for this game?
Answer: One thing that I didn't realize was that the money used in-game, used to research, and the money you start a mission with was all the same pool - I don't know why I didn't make the connection, but realizing that helped me a ton.
Anyways, some bullet points, I just recently started the game myself so there's a lot of fundamentals - I hope it's not too patronizing.

You get money back for buildings still around after the mission, so I build the better guns because having fewer guns with the same amount of firepower in most cases is easier to keep them alive. Also easier to pack together around power-up buildings.
Destroyed buildings are lost cash after the mission is over. For a while I didn't know why my money was going down even though I didn't research.
Keep out of the Titans' general walking path (usually roads) to get attacked less, and mine everything you can because that money caries over to the next missions. I prefer to build things that I end up not needing and getting refunded over not getting all the money I can from the mission because of fear of over-mining.
Use high quality barriers to block them from attacking your buildings, but don't block their path unless you need to, and be clean about placement because there's a limit to how many you can have at one time.
In order to make sure you have a good early foundation to buy those good buildings, giving you a critical level of power from the start that the enemy can't break, skip researching if you're going to start with too little money. The game will usually warn you about those things before a boss level.
For the Moon/Mars, get the blast cannons, use the blast cannons, as early as possible.
Up to 4 of the same power-up buildings can stack their effects an any given building, so if you need to, build a few in the same area.
If you have half a second of extra idle time, harvest those refineries early and reload turrets that aren't in an area with too much action, even if it's not really too low on ammo.
Comment: Side note: research no longer costs you money, you just get to research one widget per level.  Otherwise, great advice!
Answer: there is a nice little tips guide over here.  Also, it's worth noting that if you mine all crystals before the enemy spawning progress bar on the right runs out, you get a bonus $500.  And don't be afraid to use a powerup now and then, berserk on the big guys can really make all the difference.
Answer: The baddies don't start coming until after you build your refineries.  This allows you to carefully place your first few turrets (or some expensive gun power ups) before the titans start moving.  Don't spend too much cash on research if you want to maximize this advantage.
On the other hand, getting too far behind in research is bad for your campaign in the long run, so don't underspend on research either.
Comment: This is a good tip.  Note that building a droid factory also brings the enemies in my experience.
Answer: The number one tip I've found is to HOLD THE LEFT MOUSE BUTTON DOWN.  Seriously.  I try to build my refineries in a circle, so whenever I have a few seconds to spare, I hold the button down and swirl over them, again and again.  You can also reload towers without having to lift your finger.
I have also found that scanners are your turrets' best friends.  I'll throw up a half dozen plus a bunch of cheap guns to clear out the weaker enemies at long range, then, when I've gotten some more cash, I'll drop some heavier guns in to take out the big boys to have pushed closer in.
Finally, I found a tech tree that someone made up.
Have fun!!
Answer: If you are having trouble with the campaign, try playing "Endless" mode for a while.  It's fun and it seems easier to advance along the tech tree.  I was stuck on the Moon and kept restarting the campaign, but when I started playing in Endless mode I made it all the way up the tech tree without much trouble.
Answer: This is exactly my problem as well. I started from scratch two times now trying to earn/safe every bit of money but it is not enough for advanced research. At some point most enemies are heavily armored and you need the expensive guns to damage them at all. At this point it is hard to research anything anymore.
In general you should try to built the right number of refineries to mine all minerals when the last enemies are defeated. Additionally some cheap concrete barriers help your towers to survive longer as some enemies are actively searching and attacking them even if they are not in their path. You can also try to exploit the fact that the towers can be sold for their full cost up to 10 seconds after they were built.
Answer: There is almost nothing to add to guys answers except: use short-keys while harvesting, and building. it will save your expensive time. In the critical moment it is important to build fast.
Another trick is to right click on building, when you want to build the same one.
Answer: I've been playing with almost the opposite opinion - I get as many refineries down as quickly as I can at the start, starting with the most vulnerable areas first later on.
My cash builds up quickly, and with occasional use of the 20% cash booster, I can turn grouped crystals into a huge, fast influx of cash. I try and sell buildings that are in danger, but especially in the later levels, are a crucial time buffer for building up my defenses. I make heavy use of the shotgun and high-powered turrets, the disruptor, and am fairly certain things would be working out better if I would have gone for the Missile turret rather than the laser. Laser's are just so cool though.
Most missions go incredibly well - I'm only having real trouble on the last few missions of Titan. I've never run out of money though... I actually had no idea a shared cashpool was even a part of the game. I always research, every turn, without fail, and if I had a better idea of what was effective or not, I'd probably be better off.
Starting my third playthrough with that in mind.
Answer: It's worth noting that the entire game is procedurally generated. The level difficulty is a product of how much cash you have and the technologies you have researched. Therefore, you'll get an easier level with less money. Horses for courses :)
Edit: Oh, the newest version of the game doesn't require money to purchase technology. But still, the statement still stands!
Comment: *"the newest version of the game doesn't require money to research technology"* - What?  Yes it does.
Comment: I stand by what I say. None of the available research on the research selection screen when a level is about to be started has *any* cost. Previously, you'd have to pay cash. Now it's just tirered. An update removed the cost.

"Possibly making research free, meaning you simply get to choose one upgrade per level." -- 13th Dec 2010.

"Research is now free" -- 18th Jan 2011.
Comment: See http://www.puppygames.net/blog for details. Perhaps you have an old version, but it warns you when you start up.
Comment: Oh I see; the technologies are free, but the actual upgrades still cost money.


How are "first" and "second" books of the Bible pronounced?

Question: The Bible has several books in multiple parts (e.g. 1 Corintios, 2 Pedro, 3 Juan). How are these books said out loud? For example, is 1 Pedro pronounced Primer de Pedro, Primero de Pedro, Primera de Pedro, Pedro Uno, or something else?
Answer: Old Testament: All of them are "Libro de..." except for "El Cantar de los Cantares"

Books named after someone (ex: Job) While talking about it you would say "El Libro de Job" but if you are locating a reading or a quote you could say "Job 26:7"
Other titles depends, some of them are usually referred as "Libro de..." (éxodo, reyes...) and others just by the name (Génesis, Levítico, Deutoronomio...)

New Testament:

The Gospels: "Evangelio según  San...", if you want to quote them it's usual " En Lucas X:X..."
Acts is "Hechos de los Apóstoles", "Hechos" for short.
The Epistles: "X Carta de San... a ..." for example "Primera carta de San Pablo a los Corintios" for short "Primera a los Corintios"
Revelation: "Apocalipsis según San Juan" "Libro del Apocalipsis" for short "Apocalipsis"
Comment: So what would the "spoken" forms be for 1 Crónicas, 1 Pedro, and 1 Juan? Those don't seem to fit into any of those cases.
Comment: Primer libro de las Crónicas. Primera (segunda) carta de San Pedro, Primera (segunda, tercera) carta de San Juan. How they don't fit? Maybe in english Peter and John are not considered epistles? By the way Crónicas is called too "Libro de los Paralipómenos"
Comment: They are considered epistles, I just asked because your example was a letter "to" the Corinthians, not "from" a person like Peter and John. That does clear it up, so "books" are "primer de" and "letters" are "primera de."


How do I reset/change my security questions on my Apple Id

Question: I have an Apple ID and I know my password, but forgot the answer to the security question. I tried to change it at appleid.apple.com but we don't have a link to reset it. See the picture. Please help me ASAP.
Answer: You can't see the link as you only get a few attempts at getting the answers correct.
Apple Support Document

If you can't reset your security questions
Contact Apple Support in either of these circumstances:

You don't see the link to send a reset email, which means you don't have a rescue address.
You see the link to send a reset email, but you don't have access to email at the rescue address.

A temporary support PIN isn't usually required, but Apple may ask you to generate a PIN if your identity needs to be verified.


What happens when I "offline" a disk and is there a difference between diskpart.exe and the disk management snap-in?

Question:
What actions does Windows take when I "Offline" a disk in the Disk Management GUI?
What actions does Windows take when I "Offline" a disk in Diskpart?
Are there any differences between the two scenarios?
Comment: Taking a disk offline in diskpart is the same as taking it offline in the management GUI.  You may see different behavior based on the GUI having an open "session" to the offlined-disk that errors out, which is not a problem you'll encounter using disk part, or the PowerShell v4 cmdlets.
Answer: They work the same. One thing to note is sometimes the two can get out of sync.
In that case you'll need to restart the logical disk management service and restart at least the GUI.
(I feel that the cli version is less likely to trip in that situation, but it's also been a while since I last managed to sufficiently break things.)
Comment: Do you know what processes occur in either case? ACL changes, a bit flipped in the kernel, etc?


alternative to one hot encoding

Question: Hi I am working on a movie recommendation system and I have like 80.000 movies in my data set. The problem is there are like thousands of directors which is a problem when I represent a movie as a vector. One of the features of a movie is its director and I do not want my movie vector to be like 5000 in length. One hot encoding is advised everywhere but I want to do something else that will make my movie vectors small in length. I heard integer encoding but I have never seen an example of it nor it is advised. One thing that comes to my mind is to create a small interval like from 0 to 5 and let's say I have 6000 directors and I will assing first director to 0 and the next director will be assigned to 0+6/6000 and third one will be assigned to 0+2×6/6000 etc. However, I have a lot of doubts. what can you suggest? I am a rookie and not well-versed on the topic.
Answer: There are many other options instead of doing one-hot encoding. You can do target encoding, count encoding and many others. Here is a nice library for encoding categorical variables. Explore all the operations in here. Here's the link.
Target encoding would be my bet.

alternative to one hot encoding


Evaluate the following contour integral...

Question: Let $\gamma(z_0,R)$ denote the circular contour $z_0+Re^{it}$ for $0\leq t\leq 2\pi$.  Evaluate: $$\int_{\gamma(0,1)} \frac{\cos(z)}{z^2}dz$$
Comment: What have you tried? Cauchy's integral formula or the residue theorem work well here.
Answer: I don't know what you mean by $\gamma(0,1)$ but I will assume you want the closed line integral over $\gamma$. If $D=\left\{\left|z-z_0\right|<R\right\}$ then:
If $0\in D$, by Cauchy's differentiation formula,
$$\oint_{\gamma}\frac{\cos z}{z^2}dz=2\pi i f^{\prime}(0)$$
where $f(z)=\cos z$
If $0\notin D$ then $0\notin \gamma([0,2\pi])$ (so that your integral is defined) and by Cauchy's Integral Theorem,
$$\oint_{\gamma}\frac{\cos z}{z^2}dz=0$$
($f$ is analytic in $D$)
Comment: Shouldn't it be $f(z) = \cos z$? (and thus your distinction into cases isn't really necessary)
Comment: @Fabian Yeah I will edit my answer
Answer: ${\cos(z)\over z^2}={1\over z^2}(1-{z^2\over 2!}+{z^4\over 4!}-...)={1\over z^2}-{1\over 2!}+{z^2\over 4!}-...\implies$ Coefficient of ${1\over z}$ in the Laurent series expansion of ${\cos(z)\over z^2}=0\implies$ $\int_{\gamma(0,1)} \frac{\cos(z)}{z^2}dz=2\pi i\times0=0.$


Calling C function by generic pointer

Question: Is there any method to call a function, by just knowing its address in a pointer, lets say a pointer of type "void *(*)(void *)", and number and type of its parameter?
The function could have any number of parameters!
Answer: No, not in any portable or standard way.
However, there is a standard way to pass a variable number of arguments between functions.  Have a look at vsprintf.  Basically, you need a version of the function that accepts a va_list.
Answer: Roughly, no.
You have to know the number of parameters before you can write the call, and therefore the types too.  Therefore, you cannot write one line of code that accurately calls a function that takes 0 parameters or 1 parameter or 2 parameters.  You could always provide 2 and trust things will work - but the compiler will (justifiably) give warnings.

Calling C function by generic pointer