Single application of the adjoint projection.

def _apply_adj(self, a):
        # is projection the zero operator?
        if self.V.shape[1] == 0:
            return numpy.zeros(a.shape)
        '''Single application of the adjoint projection.'''
        c = inner(self.V, a, ip_B=self.ip_B)
        if self.Q is not None and self.R is not None:
            c = self.Q.dot(scipy.linalg.solve_triangular(self.R.T.conj(), c,
                                                         lower=True))
        return self.W.dot(c)