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HNQ
HNQ
4:10 AM
1
Q: Why is electric field of dipole nonzero?

thetaWhy is the electric field from a dipole nonzero? Intuitively, I know there are electric field lines going from the positive to negative charge, so there should be an electric field. But if I apply Gauss's law, then the enclosed charge should be zero (as the positive and negative charges cancel),...

electrostatics electric-fields dipole
 
 
3 hours later…
Martin Sleziak
Martin Sleziak
7:32 AM
For some context, this is related to the change in Stack Exchange software. Macros defined in the question used to be available also in answers and comments - that is no longer the case.
I have collected some information here: chat.stackexchange.com/transcript/88939/2019/1/29
21
A: The scope of \newcommand is the entire page

Adam LearIt pains me to break this thread by fixing the issue, but here we are. :) We are now inserting \begingroup and \endgroup directives into post and comment bodies, so all command definitions should be scoped to individual posts. For now, I'm only enabling this on Math (and here on meta), but barr...

Examples from Physics and Cross Validated

Jan 16 at 4:24, 2 days total – 133 messages, 1 user, 0 stars

Bookmarked Jan 18 at 13:39 by Martin Sleziak

It would be nicer to try to find all occurrences of the problem - which probably can be done from the data-dump.
However, I'd have to spend some time with programming to do that (I do not have much experience in handling XML files) and I do not have much time to try to do that now.
@EmilioPisanty Since one of the post is yours and you're among the most active editors on the site, I thought it might be worth mentioning this also to you.
However, I suppose that users of this site have noticed this change too.
 
 
3 hours later…
Emilio Pisanty
Emilio Pisanty
10:52 AM
@MartinSleziak Thanks for the heads-up
@MartinSleziak the XML in the data dump is indeed probably the place to go if this needs machine processing
i.e. to find instances where macros are defined in the question and then used in a matching answer
... but.
it's maybe sufficient to find candidate questions that define macros and then inspect by hand to see whether the answers have broken TeX
which can be done using only SQL directly on SEDE
this query indicates there's 150 questions with \newcommand's, which is low enough to go through them manually
 
HNQ
HNQ
2
Q: Scalar QED photon vacuum polarization

fogof mylifeConsider a calculation of photon vacuum polarization in scalar QED. The 1PI diagram which people calculate is this one, But in scalar QED the seagull vertex is also possible Then why not include a diagram like this one, Which would then make the propagator sum to go something like this,...

quantum-field-theory quantum-electrodynamics feynman-diagrams perturbation-theory
 
Martin Sleziak
Martin Sleziak
11:24 AM
@EmilioPisanty Well, I have already posted some examples of posts which have this problem in the link which I gave above: chat.stackexchange.com/rooms/88939/conversation/…
But I do not give any guarantees that it's all of them.
Examples of such posts (and comments) start here;
in Collecting examples of comments and posts with problem caused by begingroup..endgroup, Jan 16 at 4:36, by Martin Sleziak
These answers contain macro defined in the question.
and other posts (and comments) follow after that.
 
 
1 hour later…
Martin Sleziak
Martin Sleziak
12:41 PM
@EmilioPisanty It is interesting that search for newcommand is:q only gives 133 results.
Of course, there are also \DeclareMathOperator, \def, \let, ...
 
Emilio Pisanty
Emilio Pisanty
@MartinSleziak we can look for those (assuming that they even work on MathJax, which I honestly find doubtful) but they'll be rare exceptions
0
Q: The scope of \newcommand changed

Emilio PisantyIt was pointed out earlier today on chat, by Martin Sleziak, that the scope of MathJax new commands changed at some point in the (recent?) past: it was switched for Math SE in January of last year and on this site at some point in the intervening months. The short of it is that answers now start...

discussion mathjax
 
 
2 hours later…
Martin Sleziak
Martin Sleziak
3:04 PM
5
A: The scope of \newcommand changed

Emilio PisantyOK, I've gone through the list of answered questions. There should be no more broken LaTeX caused by this change on the site, but if you find any more, fix it on sight!

Some answers which are still broken:
I made a suggested edit for the first one. For the latter - I was not sure whether it is worth bumping a closed post.
 

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