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8h
comment How to detect loops in a vector field?
@nikie I was just trying to get as much info as possible before going in the wrong direction. I see you've already answered based on an assumption such as what I was asking for... There could be different assumptions - it could bee the curl of a vector, or you could be thinking of limit cycles in a nonlinear system, etc.
19h
comment How to detect loops in a vector field?
But the example you're using is not a physical system, and is in fact just not even a vector field because it is a discrete set of data points. So We first have to construct an interpolation. Are there any physical properties of the vector field that have to be satisfied in the interpolation? Whether lines will be closed for a given starting point will in general depend sensitively on the interpolation.
20h
comment How to detect loops in a vector field?
Do you have any particular application for this? Usually, whether flow lines are closed or not isn't really of practical importance, but one can sometimes make up special interpretations for them, see here.
1d
comment How can I evaluate untrusted Mathematica code in a sandbox?
Somewhat related: Automatically check student answers in tests
1d
comment How to get the meaning of a Mathematica symbol you don't know ?
possible duplicate of What are the most common pitfalls awaiting new users?
2d
comment 2D Fourier transform
The reason why NFourierTransform gives you an empty box is that it can only handle one-dimensional integrals. For a more robust numerical approach, you may want to look at 2D Fourier transform of a few (4) disjoint discs on a plane
Aug
24
comment Curl expression does not evaluate
Paste VectorAnalysis/tutorial/VectorAnalysis into the Help browser and go to the bottom of the page. The three cylindrical components of the function are called f, g, and h there. See also my answer here.
Aug
24
comment Curl expression does not evaluate
@Willinski Although you are correct, I don't think the question needs to be closed, because the pertinent version-8 syntax is hard to find.
Aug
21
comment How to find numerically all roots of a function in a given range?
@ShutaoTang Try adding the options ,PlotTheme->"Classic",Frame->True to Plot.
Aug
21
comment How to find numerically all roots of a function in a given range?
Very interesting! You got a mix-up in the naming: comrade should be colleague in the expression for rts. Actually, maybe one should call it companion.
Aug
21
comment Lens profile in a grid
I'm voting to close this question as off-topic because it's asking to fix code that's based on incorrect relations.
Aug
20
comment Lens profile in a grid
As @xzczd mentions, your starting equations are incorrect. Specifically, you're missing one of the in-plane magnetic field components that arise when the electric field is allowed to depend on x and y. Do you really need to use this low-level approach, or are you also interested in higher-level solutions using NDSolve? You may also want to look into RotateRight and RotateLeft.
Aug
19
comment Getting Boston Marathon Data
Perhaps you can add details of what you have already done manually, if you think it can be automated.
Aug
19
comment Getting Boston Marathon Data
If there's no public API for automated requests, this is basically a question about hacking their form submission interface to scrape the data. Therefore, the main issue is really quite unrelated to Mathematica. Have you tried anything?
Aug
18
comment Symmetrise a complicated expression
For non-polynomials, you can always use the method in my answer to What is the command to find function invariant?. But you seem to be looking for some kind of "visual" symmetry. This should be defined more clearly, I think.
Aug
18
comment Symmetrise a complicated expression
What would you do with an expression like Abs[Log[a/b]? I don't think the problem is well-defined in this form.
Aug
18
comment Can't get rid of vertical background color
I don't see this on Mac. It looks like this is an operating-system dependent bug. Are you using Linux?
Aug
17
comment Shadowing issue with DeleteDuplicatesBy
Have you tried a simpler test such as DeleteDuplicatesBy[{{a,y},{b,y},{c,z},{d,y}},Last] before doing the more complicated example in your screen shot? Or is there a reason you posted the more complicated example? Maybe it would also help to know your OS.
Aug
17
comment How to increase font size in front-end UI Menus
Help windows are notebooks, different from the menus you mention. So the answer to @MarcoB s question is quite important for a useful answer.
Aug
17
comment Using Padding with Text and Style
Yes to both. E.g., try Graphics3D[myText["{1,0,0}",{0,0,0},Padding->20,Background->Directive[Opacity[.‌​5],Red]],Background->LightBlue]. Or SetOptions[myText,Background->LightOrange].