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bio website sites.google.com/a/unca.edu/…
location Asheville, NC
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visits member for 2 years, 11 months
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I've been a professor of mathematics at The University of North Carolina - Asheville since 1997. I've been using Mathematica since I started graduate school in mathematics at Ohio State in 1989. At that time, we used version 1.1 (as I recall) to teach calculus in our Calculus and Mathematica classes. I've used it pretty much continuously in my teaching and research since then.

In addition to my posts on SE, you can find some of my papers, teaching notebooks and other Mathematica based oddities strewn throughout my website.

In recent years, I've also worked as a part-time consultant to Wolfram Research focusing on development of mathematical content for WolframAlpha.


Sep
12
comment Strange behaviour of MMA in derivatives of some standard functions
Incidentally, Derivative is not protected, so you can easily define your own DownValues: Thus, Abs'[x_] := Sign[x]; Abs'[0.5] produces 1.
Sep
12
comment Strange behaviour of MMA in derivatives of some standard functions
Well, I guess it's not just D but the general fact that symbolic computation assumes symbols are complex. Many computations performed by Mathematica must be fully understood in this context - from Simplify[Abs[x^2]] to the apparent missing branch of the cube root in Plot[x^(1/3), {x,-1,1}]. There are exceptions, particularly the CubeRoot and Surd functions introduced in V9 but, generally, computations are done in the complex numbers and I assure you that this is the context in which you need to explore your question.
Sep
12
answered Speed of ConvexHullMesh
Sep
12
comment Solve Laplace equation using NDSolve
@SantiCarmesí The gradient field issue is discussed in great detail here.
Sep
12
comment Strange behaviour of MMA in derivatives of some standard functions
A similar thing happens with Re and Im. While those functions are obviously meant to work in the complex realm, I think an understanding of what is going on there is relevant. This discussion might help in that regard.
Sep
12
comment Strange behaviour of MMA in derivatives of some standard functions
It really doesn't matter if you agree or not - the basic fact is that D works in the complex domain and these functions are not differentiable in that context. That, quite simply, is the explanation of the behavior you see. Now, whether you would prefer different behavior and how you might implement it is a different question.
Sep
12
comment Strange behaviour of MMA in derivatives of some standard functions
The functions you explore are all non-analytic as complex functions, thus the derivative is undefined. You might explore the numerical derivative ND as defined the NumericalCalculus package.
Sep
11
comment Homotopy Visualization
I did something like here to illustrate graph isomorphism. That's much simpler, though, really. Shouldn't be to hard to grab a set of points describing the boundaries of the objects but it might be tricky to maintain the topological integrity throughout the animation.
Sep
11
comment Homotopy Visualization
I guess you mean a homotopy, actually.
Sep
10
comment How do I plot the images of oriented curves under complex transformation?
How about Show[r1, r1 /. Line[pts_] :> Arrow[pts, 2]]?
Sep
9
awarded  Nice Question
Sep
9
awarded  Nice Answer
Sep
9
revised Mobius transformations revealed
added 402 characters in body
Sep
9
comment Calculating a potential function using the finite element method
@Hugh There certainly are other ways to make a mesh. In this answer I show how to interface with a free, third party program called triangle that might do what you want. However, I'd think that converting them to the ElementMesh format that you want would be rather involved. Also, V10.0.1 is due out any day and I'm quite certain that bugs in mesh generation have been addressed, though I'm not certain if this specific issue is improved or not. Will definitely be worth checking out, though.
Sep
9
awarded  Self-Learner
Sep
9
answered Mobius transformations revealed
Sep
9
comment Mobius transformations revealed
@YvesKlett Seems like a reasonable expectation. :) I do have an implementation based on simple graphics primitives that I'll post soon.
Sep
9
asked Mobius transformations revealed
Sep
9
comment Calculating a potential function using the finite element method
@s.s.o I didn't notice the {0,0} issue - thanks!
Sep
9
comment Calculating a potential function using the finite element method
@s.s.o The value of MaxBoundaryCellMeasure is ignored in your code, which is why it alleviates the problem. Using ToElementMesh directly on reg allows one to at least reduce the value of MaxBoundaryCellMeasure somewhat before the problem starts.