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22h
comment Using If statement for more than two cases
In the Help browser, look up If and follow the links under "See Also".
1d
comment Computing with matrix differential operators
Ah yes, that's because Plus inside Thread is not held unevaluated when its arguments have values that are known at the time of evaluation. To make it works for such cases it's probably best to avoid Plus - I'll edit the answer to deal with the example you gave.
2d
comment nintegrate too slow for coulomb wave functions
Please post a minimal example showing the speed issue. The loops you posted are far too long for anyone to wait through.
Dec
7
comment How to solve time dependent Optical Bloch Equations for a three level system?
Can't say anything without seeing the equations, but first order of business has to be to eliminate all unnecessary parameters by suitable rescaling. But purely symbolic solutions are unlikely to be viable for high dimensions. I don't understand whether you're using numerical coefficients or not.
Dec
6
comment 3d phase portrait for a system of DEs
@SjoerdC.deVries Terminology always depends on the context of the field. What you mean is a phase-space portrait.
Dec
6
comment 3d phase portrait for a system of DEs
@SjoerdC.deVries Yes, it's standard terminology in differential equations.
Dec
6
comment 3d phase portrait for a system of DEs
@SjoerdC.deVries In the terminology of the linked package, phase plot just means a portrait of the flow in real space.
Dec
2
comment How to “undo” SetOptions (restore defaults)
Something like this was used here, although that was about Attributes, and not Options... (+1)
Dec
2
comment How to “undo” SetOptions (restore defaults)
possible duplicate of How to restore function attributes to default
Nov
26
comment Function to calculate finite difference
@user21 Great - thanks. That's a valuable resource, I think.
Nov
26
comment Function to calculate finite difference
To answer your question, check the documentation (not very easy to find online): tutorial/NDSolveMethodOfLines - explicit formulas are above the heading for FiniteDifferenceDerivative. Maybe this should be closed as "easily found in the documentation" - but it's not that easy to find, so I could also post an answer if needed (or even better: answer your own question).
Nov
25
comment What are the steps using boolean algebra for transforming one equation into another?
Ah, sorry but that's not possible with built-in functions. You can only do it in a single step: BooleanConvert[Ykmin] gives you Ydmin except in a different order.
Nov
25
comment What are the steps using boolean algebra for transforming one equation into another?
Now the question does make sense for this forum. Not a complete answer, but a way to verify this problem is simply this: Simplify[Equivalent[Ydmin, Ykmin]] and the result indeed is True.
Nov
24
comment Getting an InterpolatingFunction from a ContourPlot
@Lou thanks - I saw there was a duplicate question just now, and marked it as such...
Nov
24
comment What are the steps using boolean algebra for transforming one equation into another?
Could you please post the Mathematica code that you've already tried. Your equations aren't in Mathematica syntax.
Nov
17
comment Negative integral of a positive function
This definitely looks like a bug that should be reported. In version 8.0.4 the integral stays unevaluated, which is better than giving a wrong result...
Nov
14
comment Labelling a subset of contours using ListContourPlot
possible duplicate of Custom contour labels in ContourPlot
Nov
13
comment Should we invest in Apple?
It depends on the weather.
Nov
8
comment What are the Mathematica functions to plot in a 3D version of elliptical coordiante system?
A Mathematica answer can not be given until the mathematical purpose of the question is clarified. It seems to be mainly a mathematics issue to which the answer would be quite broad. Is it supposed to be an orthogonal coordinate system? What, if any, symmetries is it supposed to have?
Nov
8
comment Plotting in Elliptical coordinate system
The meaning of the term "elliptical coordinate system" is that it provides a parametrization of points in a Cartesian frame, where every point is the intersection of an ellipse and a hyperbola. So to plot in this coordinate system is synonymous to forming Cartesian plot in the end, and therefore it is not clear at all what you mean by not having elliptical coordinates linked to the Cartesian ones. The name "elliptical coordinates" itself comes from the elliptical shape of the coordinate lines when drawn in Cartesian coordinates!