[GiNaC-list] How to differentiate from a Tensor?

[Vladimir V. Kisil]

>>>>> 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/