Concatenation with another :class:`SLH` object

def concatenate_slh(self, other):
        """Concatenation with another :class:`SLH` object"""
        selfS = self.S
        otherS = other.S
        new_S = block_matrix(
                selfS, zerosm((selfS.shape[0], otherS.shape[1]), dtype=int),
                zerosm((otherS.shape[0], selfS.shape[1]), dtype=int), otherS)
        new_L = vstackm((self.L, other.L))
        new_H = self.H + other.H

        return SLH(new_S, new_L, new_H)