def trmm(self,B,trans='N'):
        r"""
        Multiplication with product-form Cholesky factor. Computes
    
        .. math::
    
            B &:= L B    \text{ if trans is 'N'}

            B &:= L^T B  \text{ if trans is 'T'}
        """
        
        if trans=='N':
            pftrmm(self._V,self._L,self._B,B,trans='N')
            cp.trmm(self._L0,B)            
        elif trans=='T':
            cp.trmm(self._L0,B,trans='T')
            pftrmm(self._V,self._L,self._B,B,trans='T')
        elif type(trans) is str:
            raise ValueError("trans must be 'N' or 'T'")
        else:
            raise TypeError("trans must be 'N' or 'T'")
        return