I am new to ginac, and I want to simplify some expected values of indexed expressions. As a toy example, I wanted to simplify E[\sum_{i,j} A.i.j ^ 2] where it is known that E[A.i.j * A.i.j] = 1. The answer should be N + E[ \sum{i,j} A.i.j \sum_{k != i,l != j} A.k.l]. I tried to use the following program but it doesnt work. Any help would be greatly appreciated as I need to implement similar but more involved expressions. Thanks! #include <iostream> #include <ginac/ginac.h> using namespace std; using namespace GiNaC; int main() { symbol N("N"); symbol i_sym("i"), j_sym("j"); idx i(i_sym, N), j(j_sym, N); symbol A("A"); ex e = indexed(A,i,j) * indexed(A,i,j); cout << "e = "<< e<< endl; cout << "Free indices = " << exprseq(e.get_free_indices()) << "\n"; // I want to substitute A.i.j * A.i.j = 1, for any i,j // The following gives a run time error //ex e3 = subs(e,indexed(A,wild(),wild()) * indexed(A,wild(),wild()) == 1); // The following doesnt substitute/simplify anything idx i0(wild(),N), i1(wild(),N); ex e3 = subs(e,indexed(A,i0,i1) * indexed(A,i0,i1) == 1); cout << "e3 = " << e3 << endl; cout << "Free indices = " << exprseq(e3.get_free_indices()) << "\n"; }