test_gradient.py 文件源码

def test_undefined_cost_grad():

        # Tests that if we say the cost is not differentiable via the
        # known_grads mechanism, it is treated as such by the rest of the
        # system.
        # This is so that Ops that are built around minigraphs like OpFromGraph
        # and scan can implement Op.grad by passing ograds to known_grads

        x = theano.tensor.iscalar()
        y = theano.tensor.iscalar()
        cost = x + y
        assert cost.dtype in theano.tensor.discrete_dtypes
        try:
            theano.tensor.grad(cost, [x, y], known_grads={cost: NullType()()})
        except theano.gradient.NullTypeGradError:
            return
        raise AssertionError("An undefined gradient has been ignored.")