Art Kalb

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15 years, 206 days

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These are questions asked by Art Kalb

I am trying to get Maple to recognize that

diff(x^n,x) does not equal n*x^(n-1), but rather 0 if n=0, or n*x^(n-1) otherwise.

This comes up when differentiating an infinite sum (power series). The constant term gets transformed into n/x instead of becoming zero. Maybe this is really a bug/lack of feature in how sum/Sum works.

For example: diff(Sum(x^n, n = 0 .. infinity), x) yields


Does anybody have a fix to get the differentiation right (other than expanding some terms of the series before taking the derivative)? 

(edited) Please note I am not trying to get an answer to this specific question. It is just illustrates a simplified example of behavior that leads to other bizarre results. Please see the attached worksheet for more weirdness:


I just upgraded to Maple 2021 and started getting strange results - similar calculations seemed to work in Maple 2020.

I am looking at correlated bivariate normal distributions. When doing a fully symbolic verification of the normalization, I get an incorrect result of infinity. I also get strange results when integrating over a circular region, but the normalization seemed to be a very elementary calculation.

Maybe someone can check this make sure I'm not losing my marbles. I've attached a worksheet.



I am looking to have Maple compute the following:

simplify(diff(diff(Sum(epsilon^k*apply(index(f, k), t)/k!, k = 1 .. infinity), t), epsilon, epsilon))

The return value is:


Is there any way to get this to simplify appropriately? The problem is with the case k=1, which should just be 0.

What is the best way to expand this if I want to see some of the first few terms?


I have been trying to figure out a good way to work with z-transform expressions which display keeping everything in terms of negative powers of z. I am not using the z-transform procedure, but writing the equations directly by hand.

For example, given an expression a*z^(-1), Maple will output this as a/z. This is even more dramatic when dealing with rational forms in z^(-1).

The issue here is that z^(-1) has an explicit meaning in terms of delay blocks and causality.

If anyone has a nice way for Maple to return these in a pretty-printed fashion retaining the z^(-1) terms, that would be great. I still need to be able to manipulate the expressions algebraically.



I would like to control the extents of my 3D parametric plot. Increasing the grid creates too many gridlines and I just get a black plot  (and I still don't get the extent in the y-coordinate that I want).

Any suggestions how I might be able to get this plot from -360 to 0 and -20 to 60 completely filled in? (see attached workbook).

Any suggestions on how to control the gridlines?

An idea of what I am trying to do...I want to plot argument(z/(1+z)) vs. argument(z)*180/pi vs. 20*log10(abs(z)) with contours of argument(z/(1+z)) and 20*log10(abs(z/(1+z))
This is a 3D plot of the output phase of a Nichol's Chart (with the output contours of the Nichol's chart).


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