def solve(self, rhs, method='LDL'):
        """Return solution to self*soln = rhs using given inversion method.

        For a list of possible inversion methods, see the .inv() docstring.
        """
        if not self.is_square:
            if self.cols < self.rows:
                raise ValueError('Under-determined system.')
            elif self.rows > self.cols:
                raise ValueError('For over-determined system, M, having '
                    'more rows than columns, try M.solve_least_squares(rhs).')
        else:
            return self.inv(method=method)*rhs
dataset/ETHPy150Open sympy/sympy/sympy/matrices/sparse.py/SparseMatrix.solve/swapped operands of `<`