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

esarcush esarcush esarcush at gmail.com
Fri Jul 14 11:02:11 CEST 2017

On 7/14/17, Vladimir V. Kisil <kisilv at maths.leeds.ac.uk> wrote:
>>>>>> On Fri, 14 Jul 2017 12:15:49 +0430, esarcush esarcush
>>>>>> <esarcush at gmail.com> said:
>
>     EE> Dear all, What is right way to have something like $$> EE> \frac{\partial A^{i}_{jk}}{\partial x}$$? Indeed, I defined a
>     EE> tensor "A~i.j.k" and want to differentiate from it with respect
>     EE> to "x" e.g.
>
>     For a GiNaC object E its derivative with respect to x is obtained by
>   E.diff(x)
> --
> 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/
>

E needs to depend on x. So,

symbol A("A"), x("x");
symbol i_sym("i"), j_sym("j");
idx i(i_sym, 3), j(j_sym, 3);
ex e = indexed(A, i, j);
ex de_dx = e.diff(x);
cout << de_dx << "\n";

returns 0. Thus, what is the way to depend "e" on "x" like undefined functions?

All the bests,