itpp::mat STC::mat_pow(const itpp::mat &in_mat, int in_exp)
//square matrix power of integer exponent
{
if (in_exp==0)
{
return itpp::eye(in_mat.rows());
}
itpp::mat out = in_mat;
int abs_in_exp = std::abs(in_exp);
register int n;
for (n=1; n<abs_in_exp; n++)
{
out *= in_mat;
}
return (in_exp>0)?out:itpp::inv(out);
}