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location Amherst, MA
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visits member for 2 years, 3 months
seen 8 hours ago

I'm a retired mathematics professor who's used numerous programming languages over the years, including FORTRAN, Pascal, and APL. My current programming interests are Mathematica and J (the jsoftware.com free product), both of which I've used in teaching.


10h
answered Kronecker delta notation
1d
comment Visualization of matrix transformations
@pxc3110: See the added material at the end showing animation.
1d
revised Visualization of matrix transformations
Added section on animating the graphic
Apr
20
comment How do we make a negative integer out of a string of a negative number and vice-versa?
A negative integer is not a digit! For a given base b, the digits are 0, 1, 2, ..., b - 1.
Apr
19
comment Scan vs Map vs Apply
@Mr.Wizard: The whole point is that the link points to animations of how the various operators work! And given that the pages are copyright by Wolfram Research, I'm not sure it's legal to post even a static screenshot (would it be "fair use"?) But the animations are very useful ways to understand what Map, Apply, etc., do -- using a different modality than the usual static examples.
Apr
19
revised Visualization of matrix transformations
Added: use of GeometricTransformation.
Apr
19
revised Visualization of matrix transformations
Added: use of GeometricTransformation.
Apr
19
answered Where can I find a dark stylesheet for mathematica?
Apr
19
revised Visualization of matrix transformations
added 79 characters in body
Apr
19
answered Visualization of matrix transformations
Apr
19
comment How can I calculate the limit without using the L'Hopital's rule
To suggest correctness of the stated Lemma, in Mathematica one might look at Series[((1 + u)^(1/4) - 1)/u, {u, 0, 10}], say. (Mathematically, one still must worry about whether the series in fact converges in some interval about 0.)
Apr
19
comment Difficulties with Importing PDFs in Mathematica
I suspect the file(s) may benefit from being processed by Adobe Acrobat Pro, specifically, its Recognize Text option.
Apr
18
comment Calculating the Lyapunov Exponent/Spectrum for the Duffing Oscillator
Aside from a missing 1 from sol in the line X0[t_] = First[x[t] /. sol];, thing go bad in the 2nd call to solDuffingOscillator (to get sol2[t]). Try it first for fixed values of the parameters: subs = {a -> 0.5, b -> -8.54, c -> 14, dt -> 1, x0 -> 1, v0 -> 0, dx -> 0.5, tlim -> 1000};, sol1 = solDuffingOscillator[a, b, c, x0, v0, tlim] /. subs; X0[t_] = First[x[t] /. sol1], V0[t_] = First[x'[t] /. sol1], then solDuffingOscillator[a, b, c (X0[t] + dx), (V0[t]), tlim] /. subs`.
Apr
17
answered Scan vs Map vs Apply
Apr
11
comment Wrapping a data selection in Mathematica
@Mr.Wizard: thanks!
Apr
9
revised Wrapping a data selection in Mathematica
Add timing comparison for greater-length lists
Apr
9
answered Wrapping a data selection in Mathematica
Apr
9
comment Solving a system of two equations of third degree
I suspect that the O.P. did expect to obtain such a "closed-form explicit". While I'm well aware of Abel's Theorem prohibiting a "general formula" for higher-degree polynomial equations, particular higher-order polynomial equations can be solved, and it might have been the case that the particular system about which the O.P. asked would lead to such.
Apr
8
comment Solving a system of two equations of third degree
But this does still not give any closed-form explicit solution, as the solution still involves Root objects.
Apr
8
comment Solving a system of two equations of third degree
Let's try an example: s = 4; k = 1;. Then Reduce[{eq1 == 0, eq2 == 0}, {x, y}, Reals] yields a set of solutions involving Root expressions for eight degree polynomials!