[GiNaC-list] How to differentiate from a Tensor?
Vladimir V. Kisil
kisilv at maths.leeds.ac.uk
Tue Jul 18 10:09:24 CEST 2017
>>>>> On Mon, 17 Jul 2017 19:56:44 +0200, "Richard B. Kreckel" <kreckel at in.terlu.de> said:
RK> On 07/14/2017 11:18 AM, Vladimir V. Kisil wrote:
>> To maintainer: I have run into similar situation working with
>> differential operators. Shall we add "generic" functions to GiNaC
>> with 1, 2, 3, 4 variables?
RK> Isn't that there already?
RK> <https://www.ginac.de/ginac.git/?p=ginac.git;a=blob;f=ginac/function.cppy;h=a7e3649c7c195e93ae5886c66202ad9fdc1bbd6c;hb=HEAD#l744>
It seems, not. Assume, I want to calculate the Laplacian in polar
coordinates. Then the expression
f(sqrt(x*x+y*y),atan2(y,x)).diff(x,2)+f(sqrt(x*x+y*y),atan2(y,x)).diff(y,2)
does it, provided that f is a function of two variables without
defined derivatives. For one variable the step function is (the only?)
example of such function.
So my proposition is to add to GiNaC a family of "generic functions"
of 1-4 variables without any specific properties. Advises "derive your
own class" or "define your own function" is a certain barrier for a
set of GiNaC users, I think (from my own experience).
Best wishes,
Vladimir
--
Vladimir V. Kisil http://www.maths.leeds.ac.uk/~kisilv/
Book: Geometry of Mobius Transformations http://goo.gl/EaG2Vu
Software: Geometry of cycles http://moebinv.sourceforge.net/
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