[GiNaC-list] matrix::solve(): how to use?

Hi guys, I am tryng to solve a linear system with lsove(), with many variables being zero, so lsolve() tell that is indeterminate, but some of these entries are of interest. So, I am looking for matrix::solve and construct a matrix to solve this. Somebody have a piece of code how to make a linear system a matrix to matrix::solve ? Thanks, Marco