Compute the expectation:
    expectation[n] = <m(x_n)^T K_{x_n, Z}>_p(x_n)
        - m(x_i) = A x_i + b :: Linear mean function
        - K_{.,.}            :: Kernel function

    :return: NxQxM

def _expectation(p, linear_mean, none, kern, feat, nghp=None):
    """
    Compute the expectation:
    expectation[n] = <m(x_n)^T K_{x_n, Z}>_p(x_n)
        - m(x_i) = A x_i + b :: Linear mean function
        - K_{.,.}            :: Kernel function

    :return: NxQxM
    """
    with params_as_tensors_for(linear_mean):
        N = p.mu.shape[0].value
        D = p.mu.shape[1].value
        exKxz = expectation(p, mean_functions.Identity(D), (kern, feat), nghp=nghp)
        eKxz = expectation(p, (kern, feat), nghp=nghp)
        eAxKxz = tf.matmul(tf.tile(linear_mean.A[None, :, :], (N, 1, 1)),
                           exKxz, transpose_a=True)
        ebKxz = linear_mean.b[None, :, None] * eKxz[:, None, :]
        return eAxKxz + ebKxz