Explicitly computes the Ritz residual norms.

def get_explicit_resnorms(self, indices=None):
        '''Explicitly computes the Ritz residual norms.'''
        res = self.get_explicit_residual(indices)

        # apply preconditioner
        linear_system = self._deflated_solver.linear_system
        Mres = linear_system.M * res

        # compute norms
        resnorms = numpy.zeros(res.shape[1])
        for i in range(resnorms.shape[0]):
            resnorms[i] = utils.norm(res[:, [i]], Mres[:, [i]],
                                     ip_B=linear_system.ip_B)
        return resnorms