Hello! On Tue, Dec 07, 2004 at 01:10:09AM +0100, Andrea Bedini wrote:

Hi, I'm new to ginac, I'd like to know if is it possible to unroll indexed objects. As example, I would like to do something like this

a_i a~i = (a_1)^2 + (a_2)^2 + (a_3)^2 + ...

or just substituting a_i values in a_i * b~i

a_i = =(1,0,0) a_i b~i -> b~1

You might try this: #include <iostream> #include <ginac/ginac.h> using namespace std; using namespace GiNaC; int main(int argc, char** argv) { idx i(symbol("i"), 4); idx j(symbol("j"), 4); symbol a_1("a_1"), a_2("a_2"), a_3("a_3"), a_4("a_4"); symbol b_1("b_1"), b_2("b_2"), b_3("b_3"), b_4("b_4"); matrix a_mat(4, 1, lst(a_1, a_2, a_3, a_4)); matrix b_mat(4, 1, lst(b_1, b_2, b_3, b_4)); matrix uni_mat(4, 1, lst(1, 0, 0, 0)); ex res = indexed(a_mat, i)*indexed(b_mat, j)*delta_tensor(i,j); cout << res << endl << " ==> " << res.simplify_indexed() << endl; // This will print // [[a_1],[a_2],[a_3],[a_4]].i*[[b_1],[b_2],[b_3],[b_4]].j*delta.j.i // ==> a_4*b_4+a_3*b_3+a_1*b_1+a_2*b_2 cout << res << endl << " ==> " << res.subs(indexed(b_mat, j)==indexed(uni_mat, j)).simplify_indexed() << endl; // [[a_1],[a_2],[a_3],[a_4]].i*[[b_1],[b_2],[b_3],[b_4]].j*delta.j.i // ==> a_1 return 0; } Best regards, Alexei.