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visits member for 2 years, 3 months
seen Jun 24 '13 at 0:02

No, his mind is not for rent
to any god or government.
Always hopeful, yet discontent.
He knows changes aren't permanent,
but change is.

— Rush, Tom Sawyer


Taking an externally-imposed and much-needed break from SE activities.

E-mail (flipped ROT13): zqd˙ʎʌuzʇ@ʇɐʌǝɥʇʌssqɹǝɥɟuɹʎɔ
Any code I've posted here I place under the WTFPL.


Jun
23
comment Excel column label from integer
To clarify: if, say, the function is named spreadsheetColumn[], then spreadsheetColumn[27] should return "AA"?
Jun
23
comment How to choose three points on the circle so that the triangle is not a right triangle?
Maybe include Circle[{-2, -1}, 5] too, to facilitate visualization.
Jun
23
comment Solving this system of equations produces an error message about badly conditioned matrix
You'll want to look at Eigensystem[].
Jun
23
comment Measuring the area of non analytical regions in a plot
I don't see you mentioning your "different reasons"; if you have the points comprising your curves, you can at the very least use the "shoelace formula" or fancier methods to get a good estimate of the area.
Jun
23
comment Numerical Integration with InverseErfc
This is an answer, but apparently not for this question.
Jun
22
comment Line perpendicular to a tangent line to a parabola behaves unexpectedly
Of course it will stretch quite a bit; your setting PlotRange -> {0, 100} is hella huge. The thing is, with the default AspectRatio setting, you just won't see lines that are supposed to be perpendicular as actually perpendicular, and the Automatic setting fixes that. See Jens's answer as well.
Jun
22
comment Line perpendicular to a tangent line to a parabola behaves unexpectedly
Add AspectRatio -> Automatic and report back.
Jun
22
comment Trace of FullSimplify
"if it is possible for Mathematica to show the steps" - not in this case, I believe.
Jun
22
comment Trace of FullSimplify
In general, the simplification methods internally used by Mathematica do not necessarily correspond to how one might simplify by hand; remember that a method that is simple for computers to do is not necessarily simple for humans, and vice-versa.
Jun
22
comment How to maximize a function over a rotation matrix?
I don't have Mathematica on me at the moment, but you might try {Array[K, {3, 3}], {p, q, r}, a, b} /. Last[NMinimize[Flatten[{Total[MapThread[SquaredEuclideanDistance, {f[#, Array[K, {3, 3}], {p, q, r}, a, b] & /@ x, y}]], Thread /@ Thread[Transpose[Array[K, {3, 3}]].Array[K, {3, 3}] == IdentityMatrix[3]], Det[Array[K, {3, 3}]] == 1, a > 0, b > 0}], Flatten[{Array[K, {3, 3}], {p, q, r}, a, b}]]]...
Jun
22
comment How to maximize a function over a rotation matrix?
...and some example points would be, y'know, cool too...
Jun
22
comment How to maximize a function over a rotation matrix?
Some more definiteness would be appreciated; in particular, what would your $f$ typically look like?
Jun
22
comment Change of coordinates for an InterpolatingFunction
I'm not sure; after all, this is undocumented functionality...
Jun
22
comment How to maximize a function over a rotation matrix?
In that case, you really should edit your question to talk about your actual problem, and maybe include sample data and expected results...
Jun
22
comment How to maximize a function over a rotation matrix?
You will want to look up FindGeometricTransform[]; it will be able to find the best rigid transformation between your two sets of points.
Jun
22
comment Have the Random functions changed?
No problem; I couldn't contribute much otherwise since I'm not using a machine with Mathematica at the moment...
Jun
22
comment Have the Random functions changed?
Actually, digging deeper into old docs, it would seem that the legacy method in fact uses the rule 30 cellular automaton in the integer case. This is borne out by the fact that "Legacy" and "Rule30CA" give identical results for RandomInteger[]. In short, version 8 uses "ExtendedCA" as the default, while version 9 uses "Rule30CA" by default, for both random integers and reals. Now we wait for somebody from WRI to explain this switch...
Jun
22
comment Simplify $\cos(n \pi)$ and $\sin(n \pi)$ when n is an integer
I'm not quite sure why one works and the other doesn't, even though they are ostensibly equivalent; the reason I left a comment is because I am not at a machine with Mathematica. Might I suggest writing your own answer to your own question instead?
Jun
22
comment Simplify $\cos(n \pi)$ and $\sin(n \pi)$ when n is an integer
Did you already try Assuming[Element[n, Integers], 2/Pi Integrate[Cosh[a x] Cos[n x], {x, 0, Pi}]]?
Jun
22
comment Have the Random functions changed?
Well, for completeness' sake, could you also do tests replacing RandomInteger[{-9, 9}, 10] with RandomReal[1, 10]? Maybe use InputForm[] so that all the digits of the random variates are displayed... BTW, to cover the default method in the results of the Table[], you can use the setting Method -> Automatic.