Function isDiagonal

tests/utils/linalg.cpp:239–247

bool isDiagonal(qmatrix m) {

    for (size_t r=0; r<m.size(); r++)
        for (size_t c=0; c<m.size(); c++)
            if (r!=c && m[r][c] != 0_i)
                return false;

    return true;
}


bool isApproxUnitary(qmatrix m) {