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location Amherst, MA
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visits member for 2 years, 9 months
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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.


Oct
26
comment Solving/simplifying a trig function
What does a, whose tangent and quadrant is given, have to do with B or $\theta$?
Oct
15
comment Why does taking advantage of Listable change the results of a numerical computation slightly?
But exactly what is "compensated summation"?? Is it what's described in hal.archives-ouvertes.fr/file/index/docid/517618/filename/… ?
Oct
15
comment Total much slower in version 10
@Fred Simons: Understood why you wanted to use very same list for all 500 evaluations. I suggested varying the list just to eliminate anything special about the particular list of random numbers you might generate.
Oct
15
comment Subsitute symbolic function
In using the dot, Mathematica is just extending the traditional mathematical notation for dot products to matrix products or matrix-vector products.
Oct
15
answered Difference between double quotes
Oct
15
comment Total much slower in version 10
Just a comment that if you're trying, in effect, to average the summation over 10^7 random reals, would it not make more sense to use ls := RandomReal[{0, 1}, {10^2}], that is, with a SetDelayed?
Oct
15
comment Subsitute symbolic function
Are you mistaking matrix multiplication, which is denote with a period (.), with ordinary element-by-element multiplication, which one would denote with a space or explicit use of * ?
Oct
14
comment Integrate yields complex value, while after variable transformation the result is real. Bug?
The Assumption should be unnecessary. You'll get the same, unexpected, complex value without it, too.
Oct
8
comment Contour integration *directly*
@Dror: That's the trouble about implicit assumptions in traditional mathematical notation and understanding. One can't expect a computer language to understand such things unless you tell it.
Oct
8
comment Contour integration *directly*
@Dror: Just a bijective parametrization (except for endpoints) is not enough: use parametrization $\gamma(t) = \exp(-2 \pi i t)$ for $0 \leq t \leq 1$ to obtain $-\,2 \pi i$ for the value of the contour integer. Not so simple!
Oct
8
comment Calling Sage functions from Mathematica
Take a look at Sage functions in algebraic geometry, etc.: sagemath.org/doc/tutorial/tour_advanced.html
Oct
8
comment Contour integration *directly*
The left-hand side of the original equation is an ambiguous notation. By definition, as others have said, a contour integral requires a curve with a particular parameterization. After all, you could parametrize the unit circle by doing around it, say, twice, and then you'd get $4 \pi i$ as the value. Notation that a computer language understands is necessarily more precise than traditional mathematical notation. How is Mathematica supposed to "know" what $|z| = 1$ means??
Oct
8
comment Mathematica 10 unable to Simplify[Cos[2 ArcCos[A]]]
Comment: situations like this, where specialized functions such as TrigExpand or TrigToExp are needed, often pop up. They are seemingly counterexamples to one of the Mathematica core principles: "Automate as much as possible." (wolfram.com/language/principles)
Sep
30
revised Getting table headings when creating a table with two variables
Add example with non-default increments and example with specific value-generating function.
Sep
30
answered Getting table headings when creating a table with two variables
Sep
24
awarded  Autobiographer
Sep
22
comment Visualization of matrix transformations
Would be nice to include controls for plot range, so that so much of image wouldn't disappear when the default parameters of the linear transformation part are changed.
Sep
22
comment Visualization of matrix transformations
@DanielLichtblau: Perhaps. But I follow the lead of a classic book on differential equations & dynamical systems (was it by Arnold & Aziz) that used a cat's face to illustrate the "baker's transformation".
Sep
15
comment Incorrect result with SemanticImport
@RunnyKine: Ouch, I should have thought of Normal since it works in so many other similar situations where one has extra stuff in an object. (Series, SparseArray, GraphicsComplex, ...)
Sep
14
comment Incorrect result with SemanticImport
Setting dset = Dataset[AssociationThread[First @ data, #] & /@ Rest @ data] and din = SemanticImport["data.csv"], note that dset === din gives False, because as the FullForms reveal, they have different values for Association[Rule["ID".... What's the best way to extract just the datasets, without their IDs, so as to be able to compare?