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

[Bastian Abt]

Hi,

I want to use ginac to evaluate some complex expressions that evolve 
some vector algebra. However, have some trouble working with the matrix 
class. I have 2 questions:

     1: Am I correct, that if i want to compute the Subtraction of two 
vectors I should use the indexed variant?

     2: How do I access elements of an expression?

I have included a small file that illustrates my problem?


Kind regards,

Spooky

#include <ginac/ginac.h> #include <iostream> int main(int argc,char **argv) {
     using namespace GiNaC;
     idx d(symbol("d"),3);

     matrix m0 = matrix({{0,0,0}}), m1 = matrix({{1,0,0}});
     indexed v0 = indexed(m0,d), v1 = indexed(m1,d);

     // This seems wrong: std::cout<< (m1-m0).eval()<< std::endl;
     // -> [[1,0,0]]-[[0,0,0]] // This seems right: std::cout<< (v1-v0).simplify_indexed()<< std::endl;
     // -> [[1,0,0]].d // I can normally access matrix element using std::cout<< m1(0,0) << std::endl;
     // -> 0 // But how can I access matrix elements of an expression? // 
does not compile: // std::cout << "(v1-v0)(0,0): " << (v1-v0)(0,0) << 
std::end; return 0;
}
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