For the limit $\lim_{x\to -1}\frac{\sqrt{x+5}-1}{x+2}$, find $\delta$ that works for given $\epsilon$

Question: The question is:

I've tried it many times and no matter what I do I always get a negative delta.
Comment: How do you get a negative $\delta$ ?
Answer: This will seem a little long, but I'm going to try to break this down as finely as possible, to make the process clearer.
One way to approach this is to go backwards first, starting from the thing you want to prove.  Provided that you use invertible transformations, you should be able to reverse the analysis for your actual demonstration.
We begin with the desired condition
$$
\left| \frac{\sqrt{x+5}-2}{x+1} - \frac{1}{4} \right| < \frac{1}{100}
$$
Both the numerator and the denominator go to $0$ at $x = -1$, but the numerator has that square root in it.  We might therefore get some mileage out of multiplying this fraction by $1$, in the form of $\sqrt{x+5}+2$ divided by itself, in order to produce a difference of squares and eliminate that square root:
$$
\left| \frac{\sqrt{x+5}-2}{x+1} \cdot
       \frac{\sqrt{x+5}+2}{\sqrt{x+5}+2} - \frac{1}{4} \right| < \frac{1}{100}
$$
$$
\left| \frac{x+5-4}{(x+1)(\sqrt{x+5}+2)} - \frac{1}{4} \right| < \frac{1}{100}
$$
$$
\left| \frac{x+1}{(x+1)\left(\sqrt{x+5}+2\right)} - \frac{1}{4} \right|
    < \frac{1}{100}
$$
Now, provided that we assert that $x \not= -1$, we can cancel out the $x+1$ terms, and obtain
$$
\left| \frac{1}{\sqrt{x+5}+2} - \frac{1}{4} \right| < \frac{1}{100}
$$
It may seem as though we've merely exchanged one square root for another, and not gained anything in the process.  However, in this case, the $2$ is added to the square root, so the denominator does not vanish at $x = -1$.  Let's gather the two fractions together at this point:
$$
\left| \frac{2-\sqrt{x+5}}{4\left(\sqrt{x+5}+2\right)} \right| < \frac{1}{100}
$$
Let us multiply again by $2+\sqrt{x+5}$ divided by itself, and we get
$$
\left| \frac{-x-1}{4\left(\sqrt{x+5}+2\right)^2} \right| < \frac{1}{100}
$$
$$
\left| \frac{-x-1}{4\left(x+9+4\sqrt{x+5}\right)} \right| < \frac{1}{100}
$$
At this point, imagine that we set $x = -1+\Delta x$, where $|\Delta x| < \delta$.  We then have
$$
\left| \frac{-\Delta x}{4\left(\Delta x+8+4\sqrt{\Delta x+4}\right)} \right| < \frac{1}{100}
$$
We are now prepared to reverse our analysis to produce the demonstration.  We observe that for small $\Delta x$, the denominator is surely greater than $1$.  Therefore, let us set $\delta = 1/100$, and then
$$
|\Delta x| < \frac{1}{100}
$$
Multiplying the argument of the absolute value by $-1$ doesn't change it:
$$
|-\Delta x| < \frac{1}{100}
$$
And finally, if we divide something by an amount greater than $1$, we must surely reduce its absolute value:
$$
\left| \frac{-\Delta x}{4\left(\Delta x+8+4\sqrt{\Delta x+4}\right)} \right| < \frac{1}{100}
$$
We have now reached a point where we can "go backwards" and obtain the desired condition.
Answer: I repost it because I encountered a fatal error on the first step
$\left|\frac{\sqrt{x+5}-2}{x+1}-\frac{1}{4}\right|$
$=\left|\frac{4\sqrt{x+5}-x-9}{4(x+1)}\right|$
$=\left|\frac{16(x+5)-(x+9)^2}{4(x+1)(\sqrt{x+5}+x+9)}\right|$
$=\left|\frac{-x^2-2x-1}{4(x+1)(\sqrt{x+5}+x+9)}\right|$
$=\left|\frac{x+1}{4(\sqrt{x+5}+x+9)}\right|$
$<\left|\frac{x+1}{4}\right|$, as $x \to -1$
$<\frac{1}{100}$
.......Something like that


Buzzing in first and fifth postion

Question: I bought a used hss squier standard strat and I noticed that there is significant buzzing that goes away when touching any metal part on the guitar. It only happens when the pickup selector is in the first position or the 5th (the humbucker?!) The other three positions are fine. Is this a big problem or will I be able to fix it by myself?
Comment: Sounds like the earthing has come away from a pup or two. Try touching a bit of insulated wire between tops of  pups, and switch. If buzz disappears, then that's the problem.
Comment: Thabks for replying :). I tried doing that and it didnt remove the problem. Weirdly enough the buzz is now present in all postions. Id expect that from the single coils, but not the humbucker. Any ideas?
Answer: You have a bad ground (or earth) connection in your guitar wiring. This can be caused by a "cold solder" joint where not enough heat was applied, or a loose or broken ground wire.   To fix it requires using a soldering iron and identifying the bad connection.  In some cases it is easier to retouch all the solder connections than trying to find the one cold joint.

Buzzing in first and fifth postion


Multi-Select Picklist Alternative

Question: I am looking into the best alternative solution for data capturing and reporting. I am trying to avoid multi-select picklists.
I want to capture at the Opportunity level:

Field1__c (that contains): A, B, C, D, E options.
For each A, B, C, D, E option, there is a set of different options the user can select from

e.g.
<code>A    B
1    4
2    5
3    6
     7
     8
</code>
As a user, I need to be able to select both A and B, but also 3, 6, 7, 8 for example.
I did think of checkboxes, but due to being so many and they could potentially change so often, it is not the best solution.
I have started to create a custom object to store all the values from the multi-select picklist and a junction object that contains the categories: A, B, C, D, E. But the user needs to be able to select more than one option for both category, but also sub-category.
I am looking into the best way to capture this data, but also to create reports.
Answer: option 1: checkboxes
option 2: several single-select pick lists (and a global value set, perhaps)
option 3: custom object, child relationship for options
option 4: free text
option 5: the dreaded multi-select
none is perfect, each has pros and cons, 2 is kind of rubbish

Multi-Select Picklist Alternative


Plugins not getting updates

Question: i installed many Ubuntu on my PC and i couldn't even listen to a single music file or watch even a small video, it always says plugins not installed. If it can't even those small plugins then whast is the purpose of that whole DVD of Ubuntu...?? And what is the difference between CD and DVD of Ubuntu if it can't even install any plugin from the ??
Comment: This sounds like more of a rant then a question. Do you really want an answer? I would suggest editing your question.
Answer: First, be warned that it might not be legal in some countries, because of software patents.
With that being said, here is how to install it, click here:
ubuntu-restricted-extras
Or
you can open up a terminal and run the following command:
<code>sudo apt-get install ubuntu-restricted-extras
</code>
Select yes, and you'll have ubuntu-restricted-extras installed and working
Comment: i tried "sudo apt-get install ubuntu-restricted-extras" way, but its saying unable to locate packages "Ubuntu-restricted-extras" wht do i do now??
Comment: firstly try doing `sudo apt-get update
sudo apt-get dist-upgrade`
Comment: if this work tick this as wright answer a tick below answer

Plugins not getting updates


Shopify Hamburger Menu Button Not Working On Mobile Devices (Debut Theme)

Question: I'm using the Debut theme on my Shopify site and have an issue with the hamburger menu button not working. It will work once but when I navigate to a new page nothing happens when I press the button again. When the page loads the following message is shown on the console for theme.js:
<code>TypeError: $.debounce is not a function. (In '$.debounce(50, function() {
styleDropdowns($(selectors.siteNavHasDropdown));
positionFullWidthDropdowns();
})', '$.debounce' is undefined)
</code>
If I manually empty caches through the browser and reload the page the error no longer appears in the console and the button works again. However, once I navigate away from the page the issue returns.
Any help would be greatly appreciated.
Answer: Check to see if you have your JS files included on all pages


Format Tokens Using HTML?

Question: Is it possible to format the display results of a token? For instance, if the token is (contact.phone), is it possible to make the resulting phone number bold or a specific color?
Answer: The easiest way would be in your document. For example just make the token bold/colored in your wysiwyg editor, or if you are editing html you can do like {contact.phone}
Comment: Thank you so much. The only issue is that I have an email token and I want the resulting email link to be a certain color. But, I can't get the resulting email address link to change. I can only change the color of the token text.
Comment: Nevermind! I just figured it out. Thank you again for your help.

Format Tokens Using HTML?


Confusion in N of N-point-FFT

Question: On what basis, N of N-point-fft is chosen? What can go wrong if I don't select it to be  power of 2? How is this N related to sampling frequency?
Answer: Firstly, you need to know that the FFT computes the DFT (discrete Fourier transform) in an efficient manner. Hence, the output of an N-point FFT and N-point DFT are exactly the same.
Now, especially, if N is a power-of-two, the FFT can be calculated very efficiently. Though, if N can be factorized into rel. small prime numbers (2, 3, 5), still the calculation can be done very efficiently. Strictly speaking, the Radix-2 FFT only works, if N is power-of-two. However, in common implementations in software, N can be any number and the implementation chooses the appropriate algorithms for most efficient calculation.
Hence, if N is power of two, the calculation by FFT is just a bit faster, compared to when N would be a large prime number.
Regarding sampling frequency: If $F_s$ is your sampling frequency and $T$ is the duration of the FFT window, then $N=TF_s$. It's hard to answer more detailed what you mean by relation to sampling frequency, because I dont know exactly what you are asking.
Regarding your comment: The DFT maps a subset of the frequency range $[0,\dots,F_s]$  to the $N$ DFT-bins, which are indexed by $k=0,\ldots,N-1$. Since all frequency bins in the DFT output have the same distance to each other (i.e. they are linearly spaced), you immediately end up with $f=\frac{k}{N}F_s$, i.e. the $k$th bin corresponds to the physical frequency $f=\frac{k}{N}F_s$.
Comment: No, you first define $T$ and $F_s$. Then, within the time window $T$ you get $N$ samples (in time domain), due to sampling with frequency $F_s$.  So, you define $T$ and $F_s$ a priori, and then you get $N$. From this, after DFT, you can calculate that the value in the $k$th bin of the N-point DFT corresponds to the physical frequency $k/N F_s$.
Comment: I'm asking about this mapping formula: **f/fs=k/N**, where **f** is the analog bandwidth. I'm unable to understand it.
Comment: I added a small explanation. Is it still unclear?
Comment: " **T** is the duration of the FFT window, then **N=TFs** ". Here **T=k/N**? For example, if I take **N** =1024 and **k** is the range of samples of signal of interest e.g., **k** =750-290=460, then **f=(0.44921875)* fs**. Am I getting the formula right?

Confusion in N of N-point-FFT


Does the output signal from the FIR filter have transient response?

Question: In matlab, I have shown the signal passed through the FIR filter in the time domain. Then the beginning of the signal is like the transient response. Is the result appropriate?
Answer: Probably. Except for 1-tap filters, if your signal is of finite support, FIR filtering needs to assumes  values outside the support (before and after the values you were given)), and those values are often considered to be $0$. Hence, the extended sequence $(\ldots,0,0,x[0],x[1],x[2]\ldots)$ may produce some artifacts or transients in the output around time $[0]$, depending on the continuity and smoothness of $x$ close to $k=0$.


automatic presence validation where sql constraint doesn't allow nulls

Question: I dislike nulls in the db
I have seen too many bugs arises over the years from the sometimes surprising nature of nulls. Especially for columns we don't expect to contain nulls we can easily fail to think through their implications and get bad results. I am strong believer that emptiness for string fields (if allowed) should typically be represented in the db as an empty strings vs a null. (The worst though is allowing a mix of both where they both mean the same thing.)
So because of my experience with past problems, I've methodically considered each field and added the constraint :null => false to any field in the db that I didn't have a good reason to allow nulls. For cases where I want to allow empty strings, I set that as the default.
So far so good.
I like how ruby treats default values
As I've done this I've noticed that ActiveRecord takes my default defined in the DB and initializes the properties on the object with that value. I love that!
But this has left me wanting more. Because now I find that I am adding code like
<code>validates :name, :presence => true
</code>
every case where I've defined a not-null constraint in the db except those cases where I've chosen to provide a default empty string. But why am I repeating myself? So I'm thinking--wouldn't it be nice if ActiveRecord did this for me?
How can I add validating presence from db properties
Is there a way I can automatically create these validations for every case where there is a not null constraint in the db--except in the special case where I allow empty strings and signal that by setting that as the default?
Bonus: If there is a way to get rails to add a check for different than empty string into the db column and then only automatically add the validation of presence for string fields if they have both the not null constraint and then not empty string check, that would be truly great. Just don't know if that is possible.
Comment: Once you understand NULL-handling its nature will become surprisingly less surprising.
Comment: True, but prevention is also great. Especially when you are talking about managing a team with turnover.
Answer: I guess you can achieve something like that by adding an observer that will do the validation by default. However, I'm not sure if there's a way to cancel the action from the observer method like you could do with callbacks.


Is quiting arbitrary mode possible?

Question: How to exit arbitrary mode x, as it seams for my particular case undo-tree-mode there is no undo-tree-mode related option for undoing it, it there a general solution?
Answer: undo-tree-mode is a buffer-local minor mode, so M-x undo-tree-mode will toggle it in the current buffer.
Note that if you are in fact using global-undo-tree-mode then that is a global minor mode which controls the buffer-local minor mode in all applicable buffers en-masse, and you would want to use M-x global-undo-tree-mode to toggle that, if you wanted to disable the buffer-local mode in all applicable buffers.

Is quiting arbitrary mode possible?


Samsung 840pro SSD in RAID0... caveats?

Question: We have a SuperMicro X9SRI-F-O board that has two 6gb/s SATA3.0 ports. We currently have a single Samsung 840pro SSD hooked up to the first SATA channel. We want to double the storage and bandwidth by adding another 840pro to the other SATA channel and striping our reads/writes with RAID0.
I checked the block diagram for the motherboard, it appears the southbridge has enough bandwidth to support this setup. We'll benchmark this to make sure, and add a controller card if necessary.
First, our current SSD we don't have discard in the fstab, we simply run trim as a daily cron job. The command is fstrim -v / 2>&1 | logger -t trim. Will this work in a RAID setup?
Second, stripe size seems like a critical decision with an SSD. I've read this should be 64kb per SSD due to erase block size... leading me to think that 128k is the minimum correct stripe size. Eh?
Third, we planned to have the raid partitions use the entire SSDs. I suspect we no longer have to worry about partition alignment, since any partitions(swap) will be on top of the virtual raid device. My other thought is there may have to be a boot partition, since it's unlikely we'll have RAID0 support at boot. If this is the case, how do we align the boot and the main partition for this particular SSD?
Answers to any of these questions or advice, caveats etc is much appreciated. Thank you!
Answer: Tested in Ubuntu 14.04 trusty tahr
1) Using the whole disk, fstrim works!
2) No clue as to the correct answer here. Went with 512K.
3) No alignment problems by using the whole disk, confirmed by parted align-check opt.

Samsung 840pro SSD in RAID0... caveats?


Is there a Spanish term for a 'mandated reporter'?

Question: I am trying to describe a situation to my Spanish-speaking mother about how a friend of mine, who works with foster children, is required to report anything that was witnessed as abuse or neglect to a supervisor or the police, depending on whether the person was a child or adult.
Comment: So you are looking for a word that describes "a person that reports abuse (or whatever) but only because it is mandatory"?
Comment: Well, I tried to look for a Spanish translation of the term 'mandated reporter' because I got a court case in English, and I'm trying to translate parts of it to Spanish. It's not mandatory.
Comment: Well, by "mandatory" I meant the fact that the person reports abuse because it is mandatory. I did not mean that it were mandatory for you to translate it. I've fixed the previous comment.
Comment: Yes, all foster parents, teachers, counsellors and psychologists, pastors, and anyone who works with vulnerable children and adults, are required by law to report anything that is considered abuse or neglect. That's what I mean by mandatory.
Comment: I live in the United States, but my parents are in Mexico, so I don't know if they have a term like that in North America.
Answer: The Spanish term used within the US is denunciante obligatorio. See for instance these links:

California mandated reporter training child abuse: "Bienvenidos al Entrenamiento de Denunciante Obligatorio de Abuso de Menores – California."
Denuncias obligatorias - NYS Justice Center: "Además, la Ley de Protección de Personas con Necesidades Especiales identifica a determinadas personas que se definen como denunciantes obligatorios, y les exige a estas personas que denuncien los incidentes que afecten a personas vulnerables ante el Registro Central de Personas Vulnerables (Vulnerable Persons Central Register, VPCR) del Centro de Justicia."
thread Alaska: "Los proveedores de cuidado de niños están obligados a reportar de abuso y negligencia infantil en el estado de Alaska. Esta formación le ayudará a entender sus responsabilidades como denunciante obligatorio [...]"

You can also take a look at these bilingual Child Abuse Reporting slides.
Answer: Google Translate's choice for mandated reporter is reportero obligatorio, which sounds terrible for me. Maybe informante obligatorio could sound better but I personally recommend to use the following:

Mi posición/trabajo/situación [como padre de acogida/persona que trabaja con niños de acogida/profesor/psicólogo/whatever] me obliga a informar de los abusos y neglicencias [a la autoridad competente].

Sometimes you just can't find a proper noun in Spanish that translates a term in English, but you can always describe the situation and translate that description.
Another option could be just:

Estoy obligado a informar de los abusos.

Or:

Tengo la obligación de dar parte de los abusos a la autoridad.


Using mean length and mean weight to calculate mean BMI?

Question: Is it valid to use mean length ($h$) and mean weight ($w$)) from a given population to calculate mean Body Mass Index ($BMI = \frac{w}{h^2}$) for that population?
Comment: The question is not that abstract (per @JoeTaxpayer's comment): typical real-world BMIs (15.0-30.0) are already going to be rounded anyway to 1dp, so if the error in mean BMI due to using the ratio of means is ~ 0.05-0.1 it's mathematically negligible (<1%); for most real-world distributions of (height, weight). We're not talking about Laurel and Hardy...
Answer: Mathematically, it's not the case that these are necessarily close. It would work if it was the case that
$E(Y/X^2) = E(Y)/E(X)^2$ but this is false in general and in some particular situations it might be quite far out.
However, for a fairly realistic set of bivariate height and weight data it looks like the impact will be small.
For example, consider the model for US adult male height and weight in Brainard and Burmaster (1992) [1]; this model is a bivariate normal
in height and log(weight), which fits the height-weight data pretty well and makes it easy to get realistic simulations. A good model for females is a little more complicated, but I don't expect it would make all that much difference to the quality of the BMI approximation; I'm just going to do the males because a very simple model is quite good.
Converting the model there for male height and weight to metric and simulating 100,000 bivariate points in R before calculating individual BMIs and hence mean BMI, as well as calculating mean height on (mean weight)-squared, it turns out the result was that mean BMI was (to four figures) 25.21 and $\bar{h}/\bar{w}^2$ was 25.22, which looks pretty close.
Looking at the effect of varying the parameters, it looks like the impact of using the biased means-of-variables estimator for the women would probably be slightly larger but still not substantial enough that it's likely to be much of an issue.
Ideally something closer to whatever situation you want to use it for should be checked, but it's probably going to be pretty good.
So for a typical situation, it would seem it's unlikely to be much of a problem in practice.
[1]: Brainard, J. and Burmaster, D.E. (1992),
"Bivariate Distributions for Height and Weight of Men and Women in the United States",
Risk Analysis, Vol. 12, No. 2, p 267-275
Answer: It's not completely correct, but it will usually not make a huge difference.
For example, suppose your population has weights 80, 90 and 100kg, and is 1.7, 1.8 and 1.9m tall. Then the BMIs are 27.68, 27.78 and 27.70. The mean of the BMIs is 27.72. If you calculate the BMI from the means of the weights and heights, you get 27.78, which is slightly different, but should usually not make all that much of a difference.
Comment: Quite honestly, I would not go quite as far. Statistics is dealing with noisy data, anyway, and a slight imprecision in measuring heights or weights would dwarf the difference we have here. I'd recommend you simulate something along these lines with the data you are thinking about using, and then think about whether these tiny differences will truly have an impact on your statistical analysis.
Comment: "If you calculate the BMI from the means of the weights and heights, you get 27.78" But that's equal to the maximum of the BMIs! Getting the maximum instead of the mean seems like a big difference to me.
Comment: Thanks a bunch for your answer! So this means that this method of computation would probably not be appropriate for any type of statistical analysis, correct?
Comment: @Acccumulation - Stephan's point was dead on, but the choice of numbers didn't illustrate the situation well. BMI for "normal" is 18.5 to 24.9. The 3 BMIs in the example have a low to high range of .1. A 1/2% difference on this data is noise. A 5'8" man's BMI goes up from 27.4 to 27.5 as his weight rises from 180 to 181. 1lb is the difference between drinking a tall glass of water before or after getting on the scale.
Comment: @JoeTaxpayer: I think your point is that typical BMIs (15.0-30.0) are already going to be rounded anyway to 1dp, so if the error in mean BMI due to using the ratio of means is < 0.05 it's mathematically negligible. Correct?
Comment: The difference will not be big, and both are probably fine, but whatever you do, *please don't say you're doing one and then do the other*.That will confuse the reader who tries to replicate what you did.
Comment: @smci - When entering other data, 180,5'8"...160,5'9"....210,6'3",  the mean of the BMIs is 25.3, but the BMI of the mean data is 25.8. Now we have a divergence of .5, near 2%.  But yes, that's still small compared to the ranges. Thx.
Answer: Although I agree with the other answers that it is likely that this method will approximate the mean BMI, I would like to point out this is only an approximation.
I'm actually inclined to say you should not use the method you describe, as it is simply less accurate. It is trivial to calculate BMI's for each individual and then take the mean of that, giving you the real mean BMI.
Here I illustrate two extremes, where the means of weight and length remain the same, but the average BMI is actually different:
Using the following (matlab) code:
weight = [60, 61, 62, 100, 101, 102]; % OUR DATA
length = [1.5, 1.5, 1.5, 1.8, 1.8, 1.8;]; % OUR DATA
length = length.^2;
bmi = weight./length;
scatter(1:size(weight,2), bmi, 'filled');
yline(mean(bmi),'red','LineWidth',2);
yline(mean(weight)/mean(length),'blue','LineWidth',2);
xlabel('Person');
ylabel('BMI');
legend('BMI', 'mean(bmi)', 'mean(weight)/mean(length)', 'Location','northwest');

We get:

If we simply re-order the lengths, we get a different mean BMI while mean(weight)/mean(length^2) remains the same:
weight = [60, 61, 62, 100, 101, 102]; % OUR DATA
length = [1.8, 1.8, 1.8, 1.5, 1.5, 1.5;]; % OUR DATA (REORDERED)
... % rest is the same

Again, using real data it is likely that your method will approximate the real mean BMI, but why would you use a less accurate method?
Outside the scope of the question: It's always a good idea to visualise your data so you can actually see the distributions. If you notice certain clusters for example, you can also consider getting separate means for those clusters (e.g. separately for the first 3 and last 3 people in my example)
Comment: " It is trivial to calculate BMI's for each individual and then take the mean of that, giving you the real mean BMI." Yes, *if you have the raw data.* If all you have are summary statistics for a population, like the average height and weight, then deriving a "population BMI" from these is the best you can do, and the question of how bad an approximation that is is quite valid.
Comment: +1 Don't aggregate aggregates if you can get the same kind of answer aggregating raw data. There are answers and comments that **in this case** it makes little/no/slim/negligible difference, but don't do it. Learn and use healthy practices about data analysis, do it the right way.


Why when I try to add a point to the curve bezier I duplicate it

Question: When I try to add a point to the curve bezier ( by selecting one of the two endpoints, then holding Ctrl and clicking LMB). Sometimes Blender add a point other times Blender duplicate the same point. The photo shows the duplicate point by selecting one of the two endpoints then holding Ctrl and cliking LMB. Why?
Answer: Consider

You may be unintentionally creating a new disconnected subcurve of the entire curve object.  This happens when the active vertex is not an endpoint of the curve.  Curve objects can have many disconnected subcurves. Flexibility and Complexity.
First select an end point of the curve.  Next control-click  the location  where you want the new point to be. The new point can be moved immediately after.
Optionally Click two points and subdivide to add a new point if that suits your needs better.  The new point will be in the current curve.  Subdivide is on the menu or keystroke w.
Comment: Yes, there is new point but without line, I mean when I change to object mode doesn't appear.
Comment: Yes, there is new point but without a line joining the selected vertex of the curve, I mean when I change to object mode the new point doesn't appear.


Sublime Text URL handler for ubuntu

Question: How can I make sublime text 2 respond to txmt url scheme in ubuntu? This has been possible in OSX through subl-handler and in Windows through SublimeProtocol.
Answer: I asked me the same question today, seeing the txmt protocol with "better_errors" gem for Rails.
I search a long time but found nothing, so I tried to make it by myself.
I write an article and my blog, but I copy it here, for "future-proofness" :
Step 1
Create the file /usr/share/applications/sublime-handler.desktop
[Desktop Entry]
Name=Sublime Text 2 URL Handler
GenericName=Text Editor
Comment=Handle URL Scheme txmt://
Exec=/home/<your_user>/bin/sublime-handler %u
Terminal=false
Type=Application
MimeType=x-scheme-handler/txmt;
Icon=sublime-text-2
Categories=TextEditor;Development;Utility;
Name[en_US]=Sublime Text 2 URL Handler

Step 2: Update the MIME-types database
$ sudo update-desktop-database

Step 3: Create the ~/bin/sublime-handler file
#!/usr/bin/env bash

request=${1:23}               # Delete the first 23 characters
request=${request//%2F//}     # Replace %2F with /
request=${request/&line=/:}   # Replace &line= with :
request=${request/&column=/:} # Replace &column= with :
sublime-text-2 $request       # Launch ST2

Then make it executable : $ chmod +x ~/bin/sublime-handler
Step 4: Test a txmt:// file
If that dosen't work, say me, I'll try to help you.
Comment: Needs an additional step:

`xdg-mime default sublime-handler.desktop x-scheme-handler/subl`
Comment: from Chrome or from console(xdg-open txmt://open?url=file://%2Fhome%2Fguda%2Fclub50plus%2Fapp%2Fadmin%2Fdashboard.rb&line=26) I aways get a new browser window opened. Any ideas why?
Answer: Adding an answer, because I don't have enough reputation for a comment.
For Ubuntu 14.04, Sublime Text 3, the instructions above work. Thank you so much, @ByScripts!
In Step 3, replace:
sublime-text-2 $request # Launch ST2

with:
subl $request # Launch ST3

... and don't forget to add your own username in Step 1:
Exec=/home/<your_user>/bin/sublime-handler %u

Answer: I don't have the reputation to comment, but I would like to add to the accepted answer, that you'll need to also configure your browser to open txmt files with the new ~/bin/sublime-handler
I saved my handler in /usr/bin, which also works btw.
To configure Firefox:

go to Edit > Preferences > Applications or enter the following into the URI field
about:preferences#applications
search for txmt
on the txmt entry click on the action field and browse for your sublime-handler file

Sublime Text URL handler for ubuntu


Why can't questions with open bounty and no answers be deleted?

Question: Why can't questions with open bounty and no answers be deleted?
Comment: By design, questions with an open bounty can't be deleted. Check out the [bounty FAQ](http://meta.stackexchange.com/questions/16065/how-does-the-bounty-system-work/16067#16067) for more information (including a link to even more information).
Comment: The faq doesn't mention the rationale. I am looking for the 'why'?
Comment: Go figure. Through the long chain of links from the FAQ, despite several "Why" questions, none of them actually answer "Why"-ish, they primarily just explain what should be done (typically, flag the post for moderator attention).
Comment: Related (possible duplicate since the same ground is covered?): http://meta.stackexchange.com/questions/38819/what-happens-to-a-bounty-question-if-it-gets-migrated
Comment: More irritatingly, they can't be voted to close either.
Answer: With an open bounty? Presumably because the gauntlet has been thrown down, and someone might be working on that super-complex problem for you. It would suck if they came back for their hard-earned +500 (within the deadline) only to find the OP had deleted the question.
For off-topic / etc, ♦ moderators can still trump the bounty rules. We can even refund the original rep if we're in a good mood.
Answer: Most of the answers I have seen about bounty questions have been with the attitude of "once you open it, the points you offer for the bounty are gone into the bounty system".
This prevents people from gaming the system.
Some bounties take a good amount of work.  I know I would be upset if I saw a bounty question, spent a lot of time on it and then found out that it was gone (or not in bounty status any more).


Are there words other than "friend" where "ie" is pronounced as /ɛ/ ("short e")?

Question: Are there any words in English other than friend where the spelling "ie" corresponds to the "short e" sound /ɛ/?
Comment: To emphasize what @sumelic asked, do you mean same -spelling- as friend or same pronunciation? There are lots of words that rhyme with 'friend' but spell the vowel differently.
Comment: @Bread: do you mean as a special pronunciation just for this word, or are you talking about accents where "pen" is likewise pronounced as "pin"?
Comment: Not any common ones that I can think of, other than ones containing *friend*, such as  *friends*, *friendly*, *friendship*, *girlfriend*, *boyfriend*, etc. Wikipedia gives ***hygienic***. I guess you could try recall your *hygienic friend*.
Comment: @sumelic &Mitch. Yes. Words with 'ie'  that are pronounced with short /e/ like 'friend'.
Comment: A lot of people pronounce friend with a *short I*, as in: **frinned**.
Comment: @sumelic ~ just friend. However the short e and short i sounds are often pronounced interchangeably, depending on the surrounding consonants and other factors. In fact, it is probably the consonant **n** which causes the problem with both friend and pen.
Answer: Not any common words other than ones containing friend, such as
friends
friendly
friendship
befriend
unfriend
girlfriend
boyfriend
the open compounds
girl friend
boy friend, etc.
Wikipedia supplies
hygienic.
I guess you could try to recall if your friend is hygienic. Otherwise, a friend stays until the end. There is also the surname
Friend
as in the baseball player Bob Friend.
Comment: I don't really buy the *hygienic* example. Etymologically, that  represents /j/ (the sound of  in *yes*); it's merely coalesced into the preceding consonant, making it effectively silent. If anything, we should say that the  represents /dʒ/ (the sound of  in *job*), like the  in *region*, *allegiance*, *collegial* / *collegiate*, *theologian*, *religious*, etc. (The only difference is that those words still need the  to keep the  from being pronounced /g/, whereas *hygienic* could now be spelled as  without affecting its pronunciation.)
Comment: @ruakh: "hygiene" and "hygienic" have weird pronunciations. (I asked a [question about it on Linguistics SE](https://linguistics.stackexchange.com/questions/19270)). Normally, an "i" in this position that is not interpreted as part of a digraph, but as a "weak" reduced vowel or glide (/i~j/) would be expected to have a syllabic pronunciation because of the stress on the following syllable (compare *religiosity,* which isn't typically pronounced "relijosity"), and the preceding syllable would be expected not to have a "long i" sound (/ai/). That is, we'd expect the pronunciation /ˌhɪdʒiˈɛnɪk/.
Comment: @sumelic: Hmm, I see what you mean. Still, since etymological /dʒj/ regularly becomes /dʒ/ (as in my previous examples, as well as in the stressed syllables of words like *jury*, *injurious*, *Jew*, *June*, *jewel*), I think the pronunciation of *hygienic* is close-enough-to-regular that we can comfortably identify the  as having been absorbed into the /dʒ/ and become silent, rather than somehow merging into the /ɛ/.
Answer: Lieutenant (in British English)?
A British English pronunciation of the word lieutenant starts with /lɛ/: Collins gives "lɛfˈtɛnənt". This could be seen as a word where "ie" = /ɛ/. But this correspondence is not present for the American English speakers who use the pronunciation " luːˈtɛnənt".
Hemielytron (in American English)?
I think it's just a mistake, but the Collins website gives "hɛˈmɛlɪˌtrɑn" as the American English pronunciation of "hemielytron", and defines it as

alt. sp. of hemelytron

Personally, I would always associate the alternative spelling hemielytron with the alternative pronunciation /ˌhɛmɪˈɛlɪˌtrɑn/, but it's not a word that I use, so I can't say for sure whether anybody uses the spelling "hemielytron" and the pronunciation "hɛˈmɛlɪˌtrɑn" the way that Collins suggests.


How greatly can heat increase resistance?

Question: A conductor has a resistance of 0.001 Ohms, at room temperature, by increasing the heat x100  degrees Celsius how greatly would that effect the conductor's resistance?
I'm trying to find the correlation of heat and wire resistance.
Comment: If the resistor burns out, the resistance could be increased practically to infinity.
Comment: moving from 1 C to 100 c is NOT a 100X increase in temperature.  It only a 36% increase in temperature.  373 Kelvin vs. 273 Kelvin.
Answer: It depends dramatically on the material of the wire.

A temperature coefficient for resistance can be calculated.  See here.
Also, this related thread.
Answer: Elemental metals (e.g. Copper) generally increase in resistance at about +0.4% per Kelvin near room temperature. Alloys are often less. For hundreds of degrees C the temperature coefficient will not be a constant and you'll need to find tables or graphs to get an accurate answer for the particular material.
Answer: Typically, for a conductor, the coefficient that relates the resistivity of the material with temperature is positive. This means that when the temperature increases, the resistivity increases as well.
Here you can find a table with various coefficients, and an online calculator.
The relationship can be described by
$$
\Delta\rho = \alpha\cdot \Delta T + \rho_0
$$
where \$\Delta\rho\$ is the resistivity variation, \$\alpha\$ is the thermal coefficient for the material, \$\Delta T\$ is the temperature increase and \$\rho_0\$ is the original resistivity.
The resistance of a conductor is
$$
R = \rho\cdot\dfrac{L}{A}
$$
where \$R\$ is the resistance, \$\rho\$ the resistivity, \$L\$ the length of the conductor and \$A\$ the cross-section area.
Answer: The temperature linearly increases the resistivity of the materials assuming it doesn't get to cold or becomes so hot the material begins to liquify (as shown in figure below)
Lets say the resistivity of a material is given by
$$
\rho_{Total} = \rho_{T} + \rho_1
\\
where ~ \rho_T ~ is~equal~to~resistivity~due~to~temperature~ and~\rho_1 ~is ~the ~normal ~resistivity
$$
since resistivity is inverse proportional to the mobility of a material
$$\rho_{T}= \frac{1}{\sigma_T}=\frac{1}{en\mu_d}$$
where \$\sigma \$ is conductivity, n is free electrons per unit volume, and \$\mu \$ is the mobility of material
The key point is that
$$ \mu_d ~inversely~ proportional ~to~temperature ~$$
which then implies that the resisitivity is directly proptional to temperture.
$$\rho_T = AT$$
where A is a constant. Different materials of course will have different constants for A, but the underlying theory that temperature increases resistivity still holds
Here is a picture showing what I mean
Answer: It depends on the material of the wire.  Resistivity tables showing how the resistance of various materials vary with temperature are readily available online.


Playing YouTube videos on slow internet connection

Question: I'm using Raspberry Pi B+ model with XBMC (KODI) operating system.
I'm running on slow internet connection hence cannot stream 720p videos and buffering takes more time than playing the video.
Is there any way I can configure XBMC to run all YouTube videos at 240p / 360p (worst case).
Comment: You could always use youtube-dl...
Comment: What sorts of videos are they? If they are trailers I can point you in the direction of a script to download trailers. Otherwise, I would recommend youtube-dl and a script to grab everything from your youtube favourites.
Comment: They are normal videos - like songs / movies etc., I do not want to download them. I've downloaded youtube-dl - but it does not help me select 360p or 240p videos. That is what I want to do
Answer: Even it is an old question, it should be answered for those who come from google.
Set video quality/resolution:
Yes, you can set the quality for all YouTube videos. Because you use the Add-on called YouTube, there is the possibility to configure some settings. Open the settings in the Add-on, just where you open your subcriptions, playlists, login/logout and so on.
In the general tab, you can set the highest video quality used (if an uploaded video has only lower quality available, the lower quality will be used):

Newer Versions of Kodi have the possibility to use MPEG-DASH. If activated, it will override the General settings. There you can achive 1080p with 60fps
But I would not recommend it, if you only want lower quality. Can't even set it to lower than 480p.
youtube-dl:
In youtube-dl you can also select the video quality to download.
My internet connection is also very slow and so I download at night videos from my favorite channels and watch them later.
Configuration for quality selection is described here: https://github.com/rg3/youtube-dl/blob/master/README.md#format-selection
For example: <code>-f bestvideo[ext=mp4][height<=480]+bestaudio[ext=m4a]</code>
I can provide a complete bash script with configuration for youtube-dl if somebody needs one. With downloading thumbnails, delete old videos and embedding informations about the video from youtube in the video file, so Plex can parse them.


What time of day to feed our adult dogs?

Question: Our dogs are four and six years old. We have been feeding them twice a day since each was one year old. Recently I came across a web page that argued quite well on the reasons why it is better to feed an adult dog only once a day. That text did not say (or I missed it) what would be a good time of day for feeding.
On this site I found an answer to another question (motionsickness in a car) where the answerer said "an adult dog only needs to be fed once a day and this is usually, best done in the evening."
Okay, we are now willing to change our routine and start feeding the dogs only once a day.
Why is evening better? The food we give our dogs is dry pellets, which in my imagination makes for easy digestion. Won't the dogs then have empty stomach by the next day and won't that make them restlessly looking for the next bowlful of food? My family is away from home during the day and I'd like our dogs to calmly rest that time. Wouldn't it be good to give them food in the morning before we leave for work and school?
Comment: How long does it take solid food to go through your dogs?
Comment: @James Jenkins - I have no idea. It could be anything between 12 to 36 hours for what I can guess. The older dog eats dried out tree branches when he can, and those come out one or two days later, but I haven't bothered timing it.
Comment: I was thinking there might be a relationship between the time you feed and the time they poop. If so that might be part of the path to your answer.
Comment: There is no pattern in it. Seems more related to the amount (length 'n tempo) of outdoors walks. But even that connection is vague.
Comment: Does anyone know if feeding once a day makes an adult dog more susceptible to bloat or gastric dilatation volvulus? I prefer twice a day just so I don't need to worry (but I don't know if my worrying is founded in science or not).
Answer: Either once or twice a day are fine for most dogs. The timing doesn't matter to much either as long as they have access to an appropriate place to eliminate. One suggestion I like is to feed them a little before a long walk.  That way they can go while on the walk and they are tired and full after the walk so will be ready for a quiet day alone or a good night sleep. Any time you change your feeding schedule or amount be sure to closely monitor your dog's weight so that they don't gain or loose if it isn't desired.
If your dog has motion sickness problems then avoid feeding for a couple hours before the car ride. If it a daily car ride you might choose to feed them after you return so they are always riding on an empty stomach.
Answer: With my dogs, the Vet recommended twice a day (morning and evening), as do most food packages (although the packages usually recommend way too much food).
With water is keep it full, perhaps taking it away in the evening to prevent accidents int he middle of the night. Just as an additional FYI excessive drinking and urination is a sign of problems.
Comment: Do you happen to know if the recommendation from your vet was related to the precise food offered? I'm just wondering if the type of food makes any difference in feeding frequency.
Answer: I think there are pros and cons to feeding at any time of the day. The only thing I agree with completely is that dogs don't need to be free fed. Just like people, they can graze when bored and easily overeat.
Personally, I feed twice a day, but if someone made me choose, I'd choose morning time. I say this based on the reasoning behind feeding people and the thought that people and dogs are pretty similar. Dogs and people are both designed to eat a large meal and then have our system empty out before the next meal. This is opposed to say, a horse, whose digestive tract is designed to have something flowing through it almost constantly. This leads to the opposite problem as people often feed there horses once to twice a day.
Anyway, I know that eating a large meal right before bed can cause people to gain weight. Also, you need food energy available for building muscle and for other similar reasons. Therefore, to me, it makes more sense to feed in the morning. You have that food energy just sitting there waiting to be used. His stomach should still have a little food in it when he goes to bed, but most likely he'll need to potty well before bed and will be less likely to go during the night.
Either way you go, though. I don't think you're going to go wrong. If you look at how pack animals hunt in the wild, they go out hunting in the morning and the evening when it's cool. They rest during the middle of the day and sleep at night. They also may not catch a meal for a couple of days. So either way you choose, you're still following natural patterns.
Answer: I have a biggish dog.

Rural dog feeding strategy over here is:

if you need a more alert watch-dog for the night and prefer the dog to be sleepy during the day: feed in the morning.
if you have a barker, and want your neighbours to get some sleep during the night: feed in the evening.

These big dogs are at risk for turning their stomach, and the recommendation is to avoid activity with full stomach, and not to give too much at a time.

I usually feed him twice although he's now (at 2 1/2) able to do with 1 meal per day.
Feeding times aren't that regular in the sense that the more important rule is: food just before sleeping/nap time.
So if he has the regular morning bike run to the office, he gets his morning ration there and then has his office nap.
In the evening, he's fed last thing I do and then usually turns into his dog house after a "regional call" to the neighbouring dogs and a last inspection round of the premises.
If we're hiking whole day, he's fed afterwards the full day ration.
How much rest after feeding depends not only on the amount but also on the type of food: If you feed, let's say, a raw lung, he may take a digestive nap of 12 h before being ready to run again.
I believe he's an exception in that he's the first dog I've ever known who rarely overeats (and he's singularly unconcerned about someone else stealing his food). Also, he signs quite clearly when he's hungry and that is not always ;-).
Answer: I Personally like to feed my dogs at night because it makes them slightly more responsive to treats during the day for training purposes. Also, I don't starve them all day as I'm sure you do not. I give them interactive toys and fill them with kibble, and treat them, probably more than I should:). Although, as was stated earlier, dogs in the wild may go days before a meal and their system can handle it. We just don't want them to have to. As for weight gain, if they are otherwise healthy, it should not be an issue if you are portioning out their food and giving them plenty of exercise. Not sure about how dogs build muscle, but for humans we achieve the most gains at night. This is because our bodies produce certain hormones at night (human growth hormone for example) that cause our body to repair and grow. For humans it is best, if you are trying to build muscle, to have a meal a little before bed to give your body the energy it needs to grow. Although, you must be careful what and how much you eat. Humans, as with dogs, need to have the proper diet and exercise in order to maintain a healthy weight. It is true that you will most likely loose some weight during the night if you don't eat before bed, but this is literally because you are already starving yourself for 8 hours by sleeping. Like was said earlier, most vets recommend feeding adult dogs twice a day to maintain a healthy metabolism. This is comparable to humans eating many small meals to maintain a healthy metabolism. But, for the best results, put your dog on a routine. Feed them the appropriate amount of healthy food, and get them plenty of exercise and love, and you will be just fine.
Comment: This sounds like a good answer, but it implies the existence of a lot of supporting science, that is not linked in the answer.  Could you include references to the science you are referencing?  I know you are new to the site and not sure about how to format, don't worry about the formatting.  Just put it in there as best you can, and one of us will be happy to clean it up for you.
Comment: Digestion process is very different between dogs and humans.
Answer: I have just acquired a 2/3 year old JRT, who seriously needs expert training which I have already arranged. The Trainer states that dogs should not be fed in the morning, but rather at midday or early evening. This lady has forty years experience in dog behaviour and training. I think part of the reason is that the dog will then be more interested in treats as rewards through the training regime. Hope this helps.  Dave.
Answer: I've found this thread as I was searching for why my 15month old golden is vomiting bile in the morning.  It appears that the reason is because her stomach is empty and the lining becomes irritated.  My girl gets fed about 7.00am and between 5 and 6pm, with supposedly bedtime dog biscuits (2-3 only)about 7.30-8.00pm.  I hate to think what she may be like if I was to move to one meal a day - everyone is different, so I guess it's what suits you and your pooch.
Comment: At 15 months, your dog is (was, seeing I'm quite late to comment here) still far from grown. Once per day should be sufficient for a fully grown dog, so for a retriever may be from age 2 or 2 1/2 on.
Answer: I have two 7 year old small dogs. Have had them just over 3 months and they are rescue dogs. The Rspca only fed them once a day at midday. I feed them twice a day 7am and 4pm ish. I have halved their morning feed as they seem to be more hungry in the pm feed. I have also learnt to mix their biscuits in the wet food as they were not eating the biscuits before. I was following the food guide on the so called top level kibble packet but found they were putting on weight. I am still observing and weigh them from time to time to keep their weight in check. One dog thinks of food all day the other just when hungry.
Answer: My greyhound Missie YoKo is fed at 7.15am 1 hour before a 30 - 45min walk, she has another walk 30 - 45min in the afternoon and is fed again at 5.00pm.I feed her a raw food diet. Only one treat a week 1 single scoop of Yogurt ice cream. She is shown constant love and affection and responds positively to what is asked of her.
Answer: We looked after a dog for 8 weeks some years ago and he was a nervous wreck in the car. My animal practitioner advised giving him a slice of brown bread before a car ride because his gastric juices would have something to work on (digest) instead of them creating more nevous nausea. This worked perfectly well with that dog. Also my 4 dogs get fed at varied times each day because according to advice I got many years ago if dogs have a regular feeding regime their digestive juices are active some time before their dishes are put on the floor. Those juices are acid and can be damaging to the stomach lining unless busy with food digestion. If you feed at varied times then dogs do not learn this digestion regulating habit and therefore run less risk of problems.
Comment: Interesting advice. I disagree with what you were told about feeding due to learned gastric acids. Our human stomachs do not create acids until we eat or drink something requiring digestion. Hence, "fasting vs non-fasting" (blood draws for) lab work. I cannot see how that would differ with dogs, but I am not a Veternarian.
Answer: I have always fed my dogs twice a day at 7:30am and again at 7pm. One of my girls gets acid reflux and throws up sometimes when she has an empty stomach which is why I would feed in the evening. She even gets a little yogurt before bed to settle her stomach
Comment: The question isn't asking when you feed your own dogs. The OP heard that it is best to feed an adult dog once a day, in the evening.  Can you link to any sources online that suggest twice a day is better than once a day?
Comment: The question is asking "_what time of day to feed their adult dogs?_", and specifically "_why is evening better?_". Can you offer an answer to those questions?


Proof of $\angle$ sum of polygon.

Question: First, I know this question might have been asked by several times, see here, for an example.
Before someone may want to mark it as dulplicate, I would like to calrify what I want to ask.
Mainly, I am asking for a rigorous proof, or why it is rigorous enough?
Notes: I will be considering simple polygon.
Consider the answer of this post by Misha Lavrov,

What makes things worse is that people often work with polygons on a
  somewhat intuitive level

I agree with this.
I definitely know that
$$Interior\space\angle\space sum\space of\space a\space N-sided\space polygon=(N-2)180^\circ$$ as every high school text shall states.
Most of the proofs which I have seen about the problem, has a similar idea as the accepted answer of this post.
Main idea of the proof:
For a polygon, we will just select points to join segments, and then we can devide the polygon into several pieces, and by $\angle$ sum of $\triangle$, we can find the $\angle$ sum of the polygon.
This proof is very intuitive, but  I don't think it is rigorous enough, as I wonder, can we still connect every vertex to the point, even for a extremely ugly concave polygon, to seperate the polygon, into several $\triangle$s, such that each of the interior $\angle$ of each of the $\triangle$s is in an interior $\angle$ of the polygon and won't be counted twice. For an explaination and example for what I said right above, see below.
e.g.)
For a 'ugly' 23-sided polygon, which I drew 'randomly':
As in the image above, I discovered a way to divide the polygon into 21 pieces of $\triangle$, while it sounds to be eligible. However, I don't think this will certainly happen, if the polygon is even more ugly. How to explicitly consider the case, when different $\triangle$ share a same interior $\angle$ in the proof?
Also, as I asked above, can we always find a way to devide it properly? (I think it is important to prove it)
I also considered the way in this post.
For the induction part, asumming the $\angle$ sum formula for polygon is true for $N$-sided polygon. Then, consider any $N+1$-sided polygon, I used to think that we can select $2$ vertex which is saperate by one vertex in middle (can I present it more precisely?), join them together, and we form a $\triangle$ (Do we need to consider whether 'convex' or 'concave'?). Then we form a $N$-sided polygon, and by the induction hypothesis and $\angle$ sum of $\triangle$, we can prove the formula holds for $N+1$.
But, moreover, do we need to consider this case and/or this case, when the remaining polygon might not be $N$-sided?
TO SUM UP, How can we consider all possible cases and make a rigorous proof? Most importantly, I want a justification of the constructability(I mean whether the graph is constructable/valid, not for the Compass-and-straightedge construction)and generality of a graph, if there is a graph in the proof.
Remember, as I said above, I am looking for a rigorous proof, not an usual one.
Thank you so much for your answer :)
NOTES:Does the ways in this help?
Comment: Why not use induction. Then all you have to do is to draw a diagonal to reduce to a polygon with few sides?
Comment: @almagest Can you explain what you think with a rigorous proof as an answer?
Comment: @almagest I had been considering induction also, but I cannot complete an rigorous proof, as stated above in the post.
Answer: The key fact is that every simple polygon, not necessarily convex, can be decomposed into $n-2$ triangles by drawing $n-3$ diagonals. Then the sum of the interior angles of the polygon is equal to the sum of interior angles of all triangles, which is clearly $(n-2)\pi$.
The existence of triangulations for simple polygons follows by induction once we prove the existence of a diagonal.
For a proof, see Chapter 1 of Discrete and Computational Geometry by Devadoss and O'Rourke. This chapter is freely available.
The picture below from that chapter that captures the gist of the proof:

See also Diagonals: Feature Column from the AMS by Malkevitch.
Comment: Adapted from https://math.stackexchange.com/questions/1103253/find-a-segment-inside-a-polygon/1103318#1103318.
Comment: Sorry, I just can't find a link of the freely available chapter...
Comment: @TonyMa, see `Resources` in the book page.
Comment: oic, thanks, I will read it later.

Proof of $\angle$ sum of polygon.


Non-jewish woman converting for marriage

Question: If a non Jewish woman converts in order to marry a Jewish man are their children still considered Jewish? Even though the mother is converted and not raised in the religion.
Comment: Might not be a duplicate. The other question is specifically asking about a woman who never intended to keep mitzvot; this question just mentions that her *motivation* was marriage, but for all we know she may have intended to keep mitzvot.
Comment: This is not a duplicate- we can specify that she needs to intend to keep the mitzvot in our answers, but the question as asked is fundamentally different from the one it's purported to be a duplicate of
Comment: @Kazibácsi Whether someone intends to keep mitzvot can be a separate discussion from what their motivation for converting was.
Comment: [Welcome to MiYodeya](https://judaism.meta.stackexchange.com/a/3887/11501) Caroline and thanks for this first question. Great to have you learn with us!
Comment: @Alex If she didn't want to keep the mitzvot, for what else than a marriage did she convert?
Answer: If a non-Jewish woman converts to Judaism, she is considered to be naturalized1. This is of course assuming she had good intentions in her conversion.  If the  person in question never had intentions of keeping mitzvot (commandments) after becoming Jewish there can be complications.
But assuming the woman underwent an Orthodox conversion underneath a valid beit din (Jewish court) and was committed to living the rest of her life as a Jew, if she married a Jewish man and had children their children would be one hundred percent Jewish, no doubt about it.
Note that if the Jewish man she wishes to marry is not Torah observant, and is not willing to become so, there could be complications in the woman's conversion process.
Also, obviously someone wishing to convert to Judaism should discuss their own personal situation with their host rabbi. That way, he will be able to address the situation better.

 1. I.e. as if she were born Jewish.
Comment: And the panel of rabbis overseeing the conversion will likely try to see how sincere her intent to convert is. They may ask something like -- *if your husband disappeared from the picture, would you continue observing Judaism?*
Comment: (To OP) - In short, numerous woman convert only because they love their potential husband so much, are desperate to be married - all sorts of reasons. These reasons are insufficient to go through the conversion. A proper rabbi / bet din, would be able to detect this and not allow the conversion. I.e. the conversion has to be motivated solely by an interest and commitment to live and abide by Jewish rules and values, not just because of marriage.
Comment: It's worth reading [Yevamot 24b](http://halakhah.com/yebamoth/yebamoth_24.html#PARTb)
Comment: @DanF excellent comment overall but the phrase "desperate to be married" lends itself quite easily to misinterpretation, especially on those of the female persuasion...would you consider deleting/changing that one bit?
Comment: @JoshK First of all, I can't edit a comment. Secondly, I'll wait until some reader comments that s/he was offended and explains why, before I would feel a need to change it. It wasn't intended with any malice. FYI, my intention is that the main motive is loneliness or personal "advancement" (i.e. wanting better in life, raising a family, etc.)
Answer: Echoing Ezra's excellent answer, if a candidate is deemed to be sincere despite marriage being a significant motivating factor in her conversion, she is considered wholly Jewish just as if she had been born Jewish once the conversion is complete, except that she cannot marry a Kohain, who are a small subset of Jewish men.
From the Rabbinical Council of America (the main body setting standards and practices for Orthodox Judaism in the United States to the extent that there is one) website (italics my own):
a. Where the Conversion is Primarily for the sake of Marriage
i. Where marriage to a particular Jewish partner is a major incentive to a prospective conversion, there is an increased possibility that the geirus may come with less than the complete commitment necessary for a conversion that would be in keeping with the standards we are trying to set for the regional Batei Din. Nonetheless, experience also shows that such a motivation can result in converts of the highest caliber. Conversion for the sake of marriage therefore requires the Beit Din to constantly reevaluate if the candidate and future partner are likely to subscribe to the requisite beliefs and practices. The Beit Din must be convinced that if the potential spouse were to disappear from the candidate's life, his or her commitment to the Jewish faith and people would not waver. These factors inevitably prolong the process and make examination of the prospective convert more intense. Indeed, should the couple mention a proposed wedding date as a deadline or goal, the Beit Din should respond that the process will take significantly longer than that.
Comment: "the main governing body of Orthodox Judaism" Even in the sense that that is meaningful, it's only so in the Diaspora. In Israel it's a different story
Comment: Is the "the main body setting standards and practices for Orthodox Judaism in the United States to the extent that there is one" disclaimer sufficiently limited to satisfy your taste, @Double AA?


html listbox to show additonal txt in extra field outside of listbox

Question: I have the following db-retrieve which results in the Listbox I like to have.
But I need $desc2 to be shown under the listbox in a separate field and it must change its content when the user clicks on an other item in the list:
Here is the retrieve which works:
echo "<form action=\"admin.php\" method=\"post\">";
echo "Industry:<SELECT name=\"industry\" size=\"10\">";
$result=sql_query("SELECT cat, title, desc, parentid
                   FROM industries
                   WHERE language='english'");
while(list($cid2, $ctitle2, $desc2, $parentid2) = sql_fetch_row($result)) {
     if ($cid2==$userindustry) {
        $sel = "selected";
     } else {
        $sel = "";
     }
     if ($parentid2!=0) $ctitle2=getparentindustry($parentid2,$ctitle2);
    echo "<option value=\"$cid2\" $sel>$ctitle2</option>";
}
echo "</SELECT>

$desc2
 # place to show description of list item
      <input type=\"hidden\" name=\"op\" value=\"save\">
      <input type=\"submit\" value=\"Go\"></form>
";

As I'm now searchin for some time, but didn't found something, hopefully someone here could help me.
The code for the side is in php.
Thanks in advance.
Answer: You would have to store $desc2 to a temporary variable in the loop, and use the temporary variable after the select to show the temporary variable.
I would however, point out that in general, this is probably the wrong way of going about this code, and that your problem is deeper in your implementation :)


Dynamic selection of cache replacement policy

Question: There are some different cache replacement policies could be implemented in CPU. As far as I know, ones have better hit ratio on specific type of code than others, but if that type changes (for example, loops and scan of long file), other replacement policy may become more effective. Did somebody try to investigate how to choose a specific replacement policy at runtime using some statistic information from previous CPU usage? What is this information? Do you know some articles or books about that?
Answer: Various processors have had instructions that affect cache operations. Some examples:

Clear cache line. This takes a memory address, allocates a cache line for it, and sets all data in the memory area contained in that cache line to values with no information content (usually all zeroes). This allows then storing data without reading the cache line.
Uncached read. This takes a memory address, reads the data, but doesn't write it to the cache.
Prefetch: This takes a memory address and loads the data into cache without giving the results to the CPU. So when the data is needed later it's already in the cache, no wait needed.
Streaming: Whenever data is read, the processor starts filling either the next or the previous cache line.
Comment: Thanks. But I mean is there some statistical data or other features, which can help to determine what replacement policy should CPU choose right now?
Answer: "Adaptive Insertion Policies for High Performance Caching" (PDF) uses set dueling (where a portion of sets are assigned to different policies for tracking) to select insertion as LRU (next victim). Intel Ivy Bridge appears to use such.
For streaming accesses, one could exploit the stride-based prefetchers to detect such and choose cache bypassing (where data is not allocated to particular levels of cache), the use of specialized buffers, or the use of LRU insertion. Stride-based prefetchers retain the addresses of recent cache misses — or accesses — and check for constant offset patterns. By itself the ability to prefetch data can justify cache bypassing (the latency cost is avoided and the bandwidth-to-outer-cache cost may be acceptable), but one would typically also want to predict reuse distance (see, e.g., "Instruction-based reuse-distance prediction for effective cache management" PDF) to avoid excess refetching (when reused "soon") or cache contamination (for relatively large reuse distances).


Express the angle between two reference frames as function of other angles

Question: I'm doing my homework on flight mechanics and the first lesson is about non-inertial reference frames. I've learnt there are three basic reference frames to be account in the study of flight mechanics. Body (b), wind (w) and local horizon (h).

Body-local horizon orientation. With three angles: $\psi$ (yaw), $\theta$ (pitch), $\phi$ (roll).
Wind-local horizon orientation. With three angles: $\chi$ (wind yaw), $\gamma$ (wind pitch), $\mu$ (wind roll).
Body-wind orientation. With two angles: $\alpha$ (angle of attack), $\beta$ (slip angle).

I have determined the matrix of conversion to convert any vector from one to another frame of reference by using Euler angles, which is:
$$L_{fi}=$$
$$\begin{pmatrix}
\cos \delta_2 \cdot \cos \delta_3 & \cos \delta_2\cdot \sin\delta_3 & -\sin\delta_2 \\
\sin\delta_1\cdot \sin\delta_2\cdot \cos\delta_3 - \cos\delta_1\cdot \sin\delta_3 & \sin\delta_1\cdot \sin\delta_2\cdot \sin\delta_3 + \cos\delta_1\cdot \cos\delta_3 & \sin\delta_1\cdot \cos\delta_2\\
\cos\delta_1\cdot \sin\delta_2\cdot \cos\delta_3 + \sin\delta_1\cdot \sin\delta_3 & \cos\delta_1\cdot \sin\delta_2\cdot \sin\delta_3 - \sin\delta_1\cdot \cos\delta_3 & \cos\delta_1\cdot \cos\delta_2
\end{pmatrix}$$
Where the subindex ($fi$) indicates the final reference frame (f) and the initial reference frame (i). And the angles $\delta_1,\delta_2,\delta_3$ are to be replaced for the corresponding angles depending on our conversion.
In such a way, that if we have a vector $\textbf{A}_w$ and we want to get $\textbf{A}_h$ we'd do:
$$\textbf{A}_h=L_{hw} \cdot \textbf{A}_w$$

But I have found a problem, and here it's when my question comes, that asks you to write the following:
$$\gamma = f(\theta,\phi,\alpha,\beta)$$
That is, writing the angle $\gamma$ as function of the angles $\theta, \phi, \alpha, \beta$.
How can I do this? I have been thinking of how to do it, but how can I combine two reference frames to express the angle of another reference frame? Should I use the matrix of transformation or should I use another method?
Note: I'm not asking to get my homework done, just obtain a hint on how to do it since I've been stuck for a good deal of time.
Answer: One approach that uses the matrices you've already derived is to set $L_{bh}=L_{bw}L_{wh}$ and then solve for $\gamma$.
Comment: Thank you, I have performed the product $L_{bw}L_{wh}$ and I have equated with $L_{bh}$. In order to solve for $\gamma$, can I choose whatever row/column? I mean, will the results be equivalent?
Comment: They should be. If not, then the rotation matrices are incorrect.


Grothendieck's "Relative" Point of View

Question: I have often read that Grothendieck's insight was to put emphasis on studying the morphisms between schemes as opposed to just the schemes by themselves. What do we gain from this point of view? Why is it important that we study S-schemes, change of base, fibered products, and the like? Are there any specific concrete examples of this point of view in action?
Comment: $S$-schemes are families of schemes over $S$. This is the starting point for understanding things like moduli spaces, deformation theory, etc.
Comment: Thank you very much for this answer. A moduli space is something I can get a mental picture of, so this greatly helps. There seems to be a lot more to it though, as AreaMan's answer below seems to be of a quite different nature. Would you mind giving some more examples, or pointing me towards some references?
Comment: @AntonHilado If you are interested in learning scheme theory Ravi Vakil's notes are really great. I don't know another way to learn about this stuff other than getting into the dirty details.
Answer: Here are some examples of the strength of this point of view, taken from Ravi chapter 18.
A classic theorem: The space of global sections of a coherent sheaf on a projective $k$ variety (regular functions, regular differentials, for example) is finite dimensional over $k$. (The finiteness of the space of differentials is one way that genus can be defined in algebraic geometry.)
A similar result holds in the relative situation, in the following way: If $X$ is a projective $A$-scheme, where $A$ is a Noetherian ring, and $F$ is a coherent sheaf on $X$, then $\Gamma(X, F)$ is finitely generated as an $A$ module.
A useful consequence of this is: A projective and affine morphism to a locally Noetherian scheme is finite (meaning, the induced maps on coordinate rings of affine patches are integral). More generally, the pushforward along a projective morphism to a locally Noetherian scheme sends coherent sheaves to coherent sheaves.
If you like, this is the relative version of the statement that affine and projective varieties over $\operatorname{Spec} k$ are finite over $\operatorname{Spec} k$, i.e. just a bunch of points.
A nice classical geometry fact follows from this: A morphism between two projective varieties with finite fibers is finite.
The proof of this works in the relative projective space of $\operatorname{Spec}(A)$, and uses projective geometry intuition there (complement of a hyperplane being affine) to reach this conclusion by appealing to the aforementioned affine and projective maps are finite, which was also a consequence of the relative point of view.
Comment: Thank you very much for your answer, although I admit I'm still trying to digest this stuff. I'll check back with Ravi's notes (don't you mean chapter 17 instead of 18? Chapter 9 seems like it would be useful too). Further examples would be most welcome.
Comment: @AntonHilado Chapter 17 deals with relative proj and relative spec, which is certainly relevant. But these results about finite generation of global sections, and the corollaries I described, are cohomological results from chapter 18.

Grothendieck's "Relative" Point of View


In "Approval was given, and Ju's art displayed." how can the transitive verb 'display' be used without an object?

Question: I have read a sentence like that from a magazine:

"Approval was given, and Ju's art displayed."

Since the word display is a transitive verb, how can it be used like this without an object?
Answer: It isn't being used without an object. It's in passive voice.
First of all, there's an implied "was" before "displayed".  This disappears via a common mechanism in English grammar called ellipsis.  So the remaining "was" effectively applies both to "given" and "displayed".
And both "was given" and  "...was displayed" are to be understood as passive voice.
The object is Ju's art.
In active voice:
(Somebody) gave approval, and
(somebody) displayed Ju's art.
Comment: elision? What's elision in this?
Comment: What if it goes like this: Approval was not given, Ju's art displayed.
Comment: Ju's art *got* displayed - is there any difference then? You mean 'ellipses'?
Comment: Right you are. My bad. It's Ellipsis.
Comment: Elision is a related process, but usually operates on a segmental level.
Comment: In the negative, you'd need at least a "nor":  Approval was not given, **nor** [was] Ju's art displayed." I'd be inclined to include the "was", but it's not strictly necessary.
Comment: @BrianHitchcock Argh! you beat me to that bit while I was teaching my first lesson. Came back and there it was. However, one niggle. You say it isn't being used without an Object - but it is. *Ju's art* is the Subject of the sentence, not the Object!
Comment: @MaulikV: your example "Approval was not given, Ju's art displayed" is not good English.  Just as in the original case, there was an *and*, similarly, ellipsis of a negative verb needs to be marked with a *nor*.  So you would say "Approval was not given, nor [was] Ju's art displayed."
Comment: @araucaria: intransitive verbs have an object but no (stated) subject.
Comment: @PLL I know that. That's the reason I asked it!
Comment: @brian do you mean "passive clauses have an object but no stated subject"?
Comment: @BrianHitchcock Hi old bean. You really need to change that. The Object in an active sentence becomes the Subject in a passive sentence. We can't say that "it isn't being used without an Object" - It ***is*** being used without an Object!
Comment: @aurucaria: yes, maybe I did mean (or rather, should have said) "passive clauses". As for object vs.subject, please feel free to supply your own answer, which better addresses that aspect.
Comment: @BrianHitchcock Have rearranged my answer to make that clear, but that's not really the problem. We need the answers here to be factually correct and not misleading for learners. This particular point is not about opinions, it's about the facts of the grammar. Your answer would be superb if you corrected this point ( much better than mine). But as it stands it's damaging for learners :(
Answer: The Original Poster's Example

"Approval was given, and Ju's art displayed."

This example might be confusing for learners because it has a word missing! This isn't a mistake. It is an example of ELLIPSIS. Sometimes, we can leave out words from the sentence when the listener can understand them. The grammatical name for this is 'ellipsis'. This often happens if we have two clauses joined by and. The Original Poster's example means:

Approval was given, and Ju's art [was] displayed.

Here the second clause means Ju's art was displayed. The writer does not need to use the auxiliary was a second time. We understand the was from the first clause. This is a passive sentence, so we do not see an Object. The thing that was displayed is the Subject of the passive clause.
Notes on Objects and passives
In a declarative sentence, if the verb usually appears in transitive clauses, we will see an Object:

They shot Bob.

However, if we turn the sentence into a passive sentence, the Object in the first sentence will be the Subject in the new sentence:

Bob was shot.

Here we still understand that someone else shot Bob. Bob was not shooting anybody. He is still receiving the bullet.  But in the grammar Bob is now the Subject. So in a passive sentence, one of the Objects will become the Subject.
If a verb, like GIVE, for example, normally takes two Objects, then we will only see one of them in a passive version:

They gave [Bob] [a book].
Bob was given [a book].

The second sentence above only has one Object. This is because Bob, which is an Object in the first sentence is now a Subject in the second example. The two sentences still give us the same information though.
When we talk about transitive verbs, this is a bit misleading. We really need to talk about transitive clauses, not transitive verbs. Most "transitive verbs" can actually be used in sentences without an Object. For example, think about the verb GIVE. We can use it in an intransitive clause like this:

I'm tired of giving, giving, giving all the time.
Answer: This is to add to the two answers that understand the sentence correctly.

Approval was given, and Ju's art (was) displayed.

is an example of ellipsis (or elliptical construction), where was is omitted. This omission is not a mistake, and the sentence is not ungrammatical. The writer just uses a literary device, ellipsis.
Another matter discussed in some of the comments here is: what if the sentence were Approval was not given, ... The answer is, with ellipsis, it would become Approval was not given, nor (was) Ju's art displayed. Do not write: Approval was not given, Ju's art displayed.

The sentence is in the passive voice.
The verb display in the sentence is indeed used transitively. If it were written in the active voice, it would have been:

(We/They/Someone) gave approval, and displayed Ju's art.

In this active voice version, Ju's art is the object of the verb displayed. (And We/They/Someone is the subject of the sentence.)
IMPORTANT: With displayed being used in the passive voice in the example, Ju's art is the subject of the verb (was) displayed, not the object.

This may sound confusing: how would an object in the active voice version become the subject of an equivalent sentence in the passive voice?
Subject and object are syntactical terms, and it's important for learners to be able to identify them in sentences. Otherwise, subject-verb agreement could be a potential problem. And an object in a sentence in the active voice would become the subject of an equivalent sentence in the passive voice.
Alternately, we can maintain the relationship (thematic relation) between the two nouns in both active and passive voices by using another set of terms: agent and patient. The agent causes an action or an event upon the patient. For example,

The gallery displayed Ju's art. -- The gallery is the subject (agent), Ju's art the object (patient).
Ju's art was displayed. (by the gallery) -- Ju's art is the subject (patient), the gallery the agent.

For more details on agent and patient, this Wikipedia page could be a good starting point: https://en.wikipedia.org/wiki/Passive_voice.
Answer: Here is the original paragraph:

Seeing such promise in his student,Yang arranged an exhibit of Ju's work at the National Museum of History.Because exhibits were only of established artists, the museum director demanded that three local sculptors and one preofessional [sic] Japanese sculptor approve Ju's work.Approval was given,and Ju's art displayed.

I think it misses 'was' (also, some spelling/grammar mistakes are noticed).

Approval was given, and Ju's art was displayed

That's what the closest I can think of.

Added note: display is generally a transitive verb but not always.


What is the best chess site for strong players?

Question: A decade ago, it was clear that if you wanted to play against titled players, ICC was the best way to go. With the rising popularity of free chess servers such as lichess.org and chess.com, is ICC still the best place to play chess if you are looking for games with masters? Does chess.com have more masters/day that visit their site? I suspect that that there are significantly more titled players that play on chess.com these days but since I don't have an ICC account, I cannot verify. Anyone have any thoughts on this? Thanks.
Comment: I think this is "opinion-based". The ratings in ICC are inflated and their service is very expensive. I'll never go back to ICC, even they were free. Lichess is better and much better.
Comment: I've switched to lichess since it is free, has a decent mobile app for playing online, has useful analysis features built in the app, and is fast in finding/kicking cheaters when reported. Chess.com is very slow in dealing with cheaters, and for ICC you have to pay too much money.
Comment: I find that it is very difficult to find strong players in lichess however. It seems that the only way is to play in a tournament and that means that you will have to play many weak players just to play a strong one a couple times.
Comment: Also, SmallChess, I think this question is not entirely opinion base because the question at its core is asking which site has more strong players, which is a objective question. I didn't put lichess up there simply because it isn't popular enough to have enough strong players.
Answer: Honestly I believe that Chess.com is the best site for strong players and to gently and steadily climb up the ladder according to your rating. What I have witnessed in Chess.com is that there is a background algorithm which works for everyone and when you ask for a game it would exactly pair you up in a range which would be +400 & -400 rating points. You can even customize it according to your wish.
The benefit is if you are a 1800+ player, it would show up on the dashboard and other players would also be observing your game which is quite encouraging and you never get someone who would be too much below your rating.
Moreover, the site has infinite material resources about openings and middlegame understanding from top-level players, which makes it a great deal if you want serious progress. Even there are a lot of advertisements and strong players play there regularly, the UI is also superb.
Answer: Playchess.com, hands down, the best by test. The best interface - essentially the same as ChessBase - whereas ICC is clunky, and Chess.com is increasingly for kids.
At Playchess, 2000 players play like 2000 players, and 1400's play like 1400's. I find the rating strengths fairly equivalent to OTB tournament strength.


Marketing Cloud Enhanced FTP logs

Question: Does Enhanced FTP log IP addresses from users? I mean a history of IPs, logins.
Comment: If my answer helped, please mark it as accepted so others can easily see this has been solved. Thank you!
Answer: At least this data isn't available to the user/administrator. However I am sure the data is is being logged, but only accessible by Salesforce Marketing Cloud technical support staff. The "Activity" section of FTP account administration covers changes made to the configuration (e.g. the password, etc.) only.
So if you need any specific data you will have to create a support case in order to have someone retrieve the data for you. (NOTE: I guess this counts as developer support and therefore you need to be enrolled to the premier success plan)

Marketing Cloud Enhanced FTP logs


iPad stolen with LastPass, Should I be worried?

Question: Unfortunately my iPad was recently stolen and I had LastPass installed on it. Both the iPad and the app are protected with TouchID and passcodes. However, LastPass keeps an encrypted offline cache of the passwords and other stuff including secure notes for bank accounts and cards, etc. I understand that it should be very unlikely for someone to get through TouchID and the master password for the app. Just in case, I can go ahead and change the password for all the critical websites, but I can't change anything about the bank accounts and other secure notes already in there. Should I be worried about someone getting the vault decrypted? I'm assuming the everyday petty thief wouldn't go through all that but some advice could still be helpful.
Comment: You answered your own question, unfortunately. It is **unlikely** that someone could break through the protections. It is **unlikely** that the average thief would go through all that work to try. But it's *possible*. I know you want some certainty, but we'd be guessing.
Comment: Did you set up your iPad with "Find My Phone"? You could remotely wipe it.
Comment: @schroeder Yeah, I have that set-up, but it's a wifi only model and they can't connect to any wifi network unless they can unlock it first. Kind of a chicken and egg situation..
Answer: LastPass promises to that your password database can only be decrypted if the attacker knows your master password. So if you trust LastPass, you don't have anything to worry about.
However, given that LastPass is closed-source software, there is no way to actually verify this promise, and hence the security is based upon your trust in the company.
Still, given that you trusted the company enough to become a paying customer, there is no need to change any of your passwords. They simply cannot be uncovered without knowing the master password.
Comment: I'm not sure you're understanding the question.  The asker is concerned about the password cache stored locally on the iPad which is used in the case where the master password is lost. Answering the question would entail knowing how to go about attacking this locally stored password cache and the feasibility of that.


Do FeatureLayers reproject their features to adapt them to the map projection?

Question: I'm working with the ArcGIS Flex API.
For example, ArcGISDynamicMapLayers do reproject their data in order to make it in the same projection as the map.
Do FeatureLayers have the same behaviour?
Comment: Just a small clarification: The ArcGISDynamicMapLayers are not projected in the client's Flash player. The Images themselves are requested in the appropriate projection. It is ArcGIS server which does the reprojection.
Comment: Here's an article I wrote about this. Might be helpful... particularly the performance considerations for mixed spatial references... http://www.spatialexception.org/posts/arcgis-server-spatial-reference-faqs
Answer: The answer is Yes.
Have a look at this sample: Generalized Data.
If you have a look at the Original Services, the Feature service is wkid:4267, while the map and the tiled map service are in wkid:3857/102100.
If you have a look at the service call using Firebug, you will see that the data is requested in wkid 102100:
Comment: This is because wkid=2154 is in a different datum. When you try to project from one datum to another, you need to use a transformation. ArcGIS server by default, uses the default transformation, which might not be the best for your Area. AFAIK, there is no way to ask ArcGIS server to use a particular datum transformation. Your best bet is to publish the original service in WGS84 datum, so as to get proper projection.
Comment: If a default transformation is known. In the case of AGD66/WGS94 or AGD66/GDA94 unless a transformation is supplied the features will be 200m (approx) displaced. I'm sure more cases like this exist, this is just one I've come across. It is always best to keep your features in the same projection if possible and datum if not; the performance cost for project-on-the-fly is less than it used to be but it could still 'cost' in the views-per-second.
Comment: Ok. But it seems that the reprojection is not correctly made in the case of the feature service I'm using ?!
I have a map projected in wkid=102100. A feature service calls some data projected in wkid=2154. The data from the feature service doesn't appear exactly where it should appear. It's moved by ~20 meters.
I made some research and the answer may be that ArcGIS needs the "grid of correction" between the projections Web Mercator and Lambert93.
Is that the answer? If yes, how can I do it?


How to describe the relation between a course instructor to his teaching assistant?

Question: How do you describe the relation between a course instructor to his teaching assistant? Is he the "teaching supervisor" to his TA? This is encountered during PhD application. Thanks!
Comment: @user14449: I wouldn't be so quick to say that a professor wouldn't mentor his teaching assistants with respect to honing their teaching skills. Also, the question is asking for another word to describe "the professor for whom I served as a teaching assistant." While scaaahu's answer isn't 100% correct, it's not completely wrong, either.
Comment: I actually disagree with scaaahu above quite strongly. You are just his/her teaching assistant. There is no need for further description, because quite often, you just grade his assignments, or lead tutorial sessions, or you do other trivial things that helps the course run smoothly. The instructor usually provides minimal directions, and he/she would definitely not think of themselves as your mentor.
Comment: I think the answer is between supervisor and mentor.
Comment: I agree that "mentor" is a terrible choice (never use "mentor" like it's a job title).  I would usually write something like "TA for course MATH XYZ, taught by A. Nobody."  If the professor actually provided some kind of training or something, you can discuss that, but otherwise phrase things in terms of your relationship to the course, not the professor.
Answer: It sounds like the question is that you need to fill in the "In what context have you known the applicant" box on a PhD recommendation letter.
If this is the case, then, for this particular point, I would not list "research supervisor," since this is clearly a teaching situation. However, "student" also doesn't make any sense. So, if there's no specific option which clearly satisfies this, I would check off the "other" box, fill in "teaching supervisor," and then explain the relationship clearly in the text of the recommendation letter itself.
Comment: "I was her teaching assistant" also works.


Change user password while password is empty

Question: I have a realy strange problem in Ubuntu 11.10. I have by accident my password set to empty. If I wan't to install software now the system asks for a password, but I haven't one anymore. If I enter my old password it sais it's wrong and if I leave it empty it also does. Now I wan't to set my password back, but the system asks for the old password before I can change it. That password doesn't exist, so I can't do anything anymore! Can someone help me please?
Comment: I can't understand why Ubuntu accept an empty password if you can't enter it anywhere...
Answer: Try running passwd from a terminal. It'll ask you for your old password, and then for your new one.
If it doesn't accept the old one there, run sudo passwd <username> replacing <username> with your username. That will make sure you can change it without the need for your old one, in the hope that it accepts the sudo password.
Comment: Not if the password is blank! This is useful trick, thanks RobinJ.
Comment: when you try sudo passwd then you need to old-password for execution of passwd command (Due to sudo......)
Answer: You will need to boot in to recovery mode (press shift key after BIOS post and keep it pressed until the grub menu is shown) and drop to a root console. There you will be able to change the password for your current user.
Here you can find a very good example of what to do to reset your password.
Comment: Thank you for the answer. My next problem is that I get an authentication error or something like that. What am I doing wrong?
Comment: Where do you get the fault at? Can you paste the output of the fault, when do you get the fault?
Comment: I get the error when I wrote the password for the second time. I don't have time for trying again so I can't give the whole error now.


Composites from -σις words

Question: How does one form composites from words in '-σις'?
For example, if one wishes to name the fear of vaxing fat,
using πάχυνσις, is it παχυνσοφοβία; or παχυνσεοφοβία?
Answer: My expectation would be that the base stem would be used, thus παχυνσιφοβία.  I haven't found a lot of examples to support this, but there is, for example, πραξι‐κοπεῖν "to take by surprise" from πρᾶξις and στασι‐ωρός "watcher of the station" from στάσις.
P.S. What's "vaxing fat"?

Composites from -σις words


Do dummy variables remove the need for covariates?

Question: This may sound like a rudimentary question, but I am curious if dummy variables reduce or eliminate the need for certain other controls. For instance, if I am looking at the impact of some variable X_1 that is at a CITY level (across several countries) and want to use some X_2 as a control - if X_2 is only available at a COUNTRY level, then wouldn't a COUNTRY dummy variable capture all relevant variance anyway and eliminate the need for X_2 as a control in estimating X_1?
Comment: The general answer is "No". If you want a more specific or detailed answer you should give all the details on the framework. Do you speak about the linear model,
and ask about under which circumstances $\beta$ is significant in
$$ y_{nt} = \alpha + x_{nt}\beta + u_{nt}  $$
but no longer significant in
$$ y_{nt} = \alpha_n + x_{nt}\beta + v_{nt},$$
where the error term $ v_{nt} $ is assumed to be orthogonal to $X$ ?
Comment: Per the below, the data is a cross-section rather than a panel. So I am looking at the difference between:

( y = a + x_1*B_1 + x_2*B_2 + countrydummy*B_n + u )

vs.

( y = a + x_1*B_1 + countrydummy*B_n + v )

I'm not good with latex but you can imagine a subscript of _i for each of these representing city i.

Would the estimate for B_1 be consistent across both?
Answer: No it is not guaranteed it will solve the problem. The fixed country dummy would capture all relevant effects that are time invariant.
Now in principle you could also add time fixed effects but that's still no panacea because time fixed effects assume the time effect is spatially homogenous.
If you believe that $X_2$ is something that varies across time and has heterogenous effect (e.g. output of firm, number of pupils per school etc) then you still need to control for $X_2$.
Comment: The data is a cross section rather than a panel. So let's say X_1 is percentage of people in each city in poverty, X_2 is the country gdp per capita (which is the same for every city in a country in the cross-section) and then we also have a dummy variable for each country. If all I care about is understanding the impact of X_1 on some given Y, do I need to include X_2 or will the dummy suffice to capture all relevant country-level effects?
Comment: @JKim59817 dummy would suffice for the regression to be unbiased but A) you will need a lot of observations in each sub unit in your cross section since every country dummy is another non-deterministic parameter. B) it would be strange not to use easily findable GDP. Even if reg with dummies would be unbiased you would get more from the reg with actual variable interpretation-wise. If I would be conference/workshop participant, and you would say you did this for easily measured variable like GDP I would raise that as an issue
Answer: My answer is "Yes" for your specific question with $X_2$ being available only at the country level. (No if $X_2$ is a general variable.)
Country dummies eliminate the need for $X_2$ as a control because $X_2$ is perfectly predicted by the country dummies. More technically, $X_2$ and $m-1$ country dummies ($m$ = number of countries) are perfectly collinear. If you regress $y$ on $X_1$, $X_2$ and country dummies, $X_2$ or one country dummy will be omitted depending on which of x2 and i.country is specified first.
That said, please make sure that the two models (one with $X_2$ and without country dummies, and the other with country dummies) are two different models because one controls for only $X_2$ while the other controls for all cross-country heterogeneity. You can also compare the $X_1$ coefficients from both models for whether $X_2$ is sufficient as a control, which can be interesting.