[GiNaC-list] How to access matrix elements of an indexed expressions

[Christian Bauer]

Hi!

On 11.01.25 10:40, Bastian Abt via GiNaC-list wrote:
>      1: Am I correct, that if i want to compute the Subtraction of two vectors 
> I should use the indexed variant?

Use evalm().

>      2: How do I access elements of an expression?

You could use numeric indices:

#include <ginac/ginac.h>
#include <iostream>

int main(int argc, char **argv) {
     using namespace GiNaC;

     matrix m0 = matrix({{1, 2, 3}}), m1 = matrix({{6, 5, 4}});
     std::cout << (m1 - m0).evalm() << std::endl;
     // -> [[5,3,1]]

     idx i1(1, 3);
     std::cout << indexed((m1 - m0).evalm(), i1) << std::endl;
     // -> 3
}

Bye,
Christian

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