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16h
comment Transform Spherical coordinates to Cartesian?
This is just a matter of looking up the help under VectorAnalysis/tutorial/VectorAnalysis. The command you need is CoordinatesToCartesian.
16h
comment Intersection of two vector spaces
To give a useful answer, it would help to know what have you tried and what you mean by "manually" computing matrices (i.e., does a sequence of Mathematica commands count as "manual"?).
1d
comment How to “Copy as Unicode” from a Notebook?
On my Mac this answer works fine (including the copy button) in Mathematica versions 8 and 10.
2d
comment Export[] performance
On my Mac, with Mathematica version 8, the h5 export is still faster than the BinaryWrite: the result were: {0.575183,test.h5}, and {0.588023,Null} respectively.
2d
comment Problems with plotting the imaginary part of an eigenvalue
Yes, I would answer the same way. Maybe you can add that k=0 is a point of degeneracy, which causes the kink in the plot: the eigenvalue is not required to follow a differentiable curve through such a point. However, you could define the "correct" plot by switching between eigenvectors 3 and 4 at k=0.
Sep
18
comment Solution to a T+U = E equation
I've added some more explanation and also addressed your original InverseFunction approach in my edited answer.
Sep
17
comment HoldForm doesn't hold form
@Mr.Wizard I'll look at it when I get a chance to upgrade. I'm currently happily using a computer with only version 8 installed.
Sep
17
comment Conceptual understanding of patterns
You seem to be talking more about Maxima than Mathematica. Are you aware that in Mathematica, both x_ and _x have a meaning as patterns (but are different)?
Sep
16
comment Strange opacity behavior
Thanks for doing the comparison of approaches in your answer here, which I strangely overlooked until now.
Sep
15
comment Strange behaviour of MMA in derivatives of some standard functions
I tried to figure out what the question is about, but I honestly can't think of any way to answer here.
Sep
15
comment Strange opacity behavior
I think you should do the second code block first. Lately I've been using that trick in the form of a function, see e.g. here.
Sep
13
comment Mathematica isn't sure whether a sum of two positives is positive or not
@jim Since I don't know what prevents Refine from working, it will be very hard to give a general cure for this problem. Here is another idea: see if you get an empty set by applying Assuming[0 < x < 1 && 0 < y < 1 && 0 < z < 1, FindInstance[$Assumptions && Not[statement], {x, y, z}]]. That's all I can think of right now.
Sep
12
comment Plotting an orbit using first principles
If the goal is to do the time-stepping yourself, then I think it's a duplicate of RK4 Gravity Simulator.
Sep
12
comment What is the equation to plot a vertical line?
A related question is Calling Correct Function for Plotting DiracDelta. Not the same because the plot has value 0 away from the spike.
Sep
12
comment Solve Laplace equation using NDSolve
@SantiCarmesí For the gradient and field strength, you can use my answer here. The error message in the potential plot appears because the inner boundary isn't sampled quite accurately. One can get rid of this by first defining rm=RegionMember[\[CapitalOmega]] and then replacing the plot argument sol[x,y] by If[rm[{x,y}],sol[x,y],100].
Sep
12
comment How to get an Excel-like surface plot with ListContourPlot3D
Isn't "Excel" - "like" a contradiction in terms?
Sep
11
comment Is there a built-in function which detects singularities in a function?
@Artes I agree on the closeness because the intention here was originally to find points of non-differentiability, too. But I interpreted the usage of "singularity" here to be more general. E.g., Abs[x]^2 would be differentiable but still singular.
Sep
11
comment Is there a built-in function which detects singularities in a function?
Clearly FunctionDomain can yield True for non-analytic functions, such as the third one (or anything with singularities in higher derivatives). But it does detect the Tan singularities (as does my answer).
Sep
11
comment Is there a built-in function which detects singularities in a function?
@Dr.WolfgangHintze I added the arbitrary c because I can't specify a numerical expansion center, since that may happen to be a special point of singularity. E.g., 1/x can't be expanded around 0, but it can be expanded around c. So I avoid unnecessary error messaged this way. Maybe this could be eliminated if instead I catch such errors differently...
Sep
11
comment Is there a built-in function which detects singularities in a function?
@Szabolcs That's true - it may even be part of the symbolic processing step. For example, if I define ff[x_?NumericQ] := Sign[x] then Plot[ff[x], {x, -1, 1}, ExclusionsStyle -> Red] doesn't show any detected exclusions.