test_gradient.py 文件源码

def test_downcast_dtype(self):
        # Test that the gradient of a cost wrt a float32 variable does not
        # get upcasted to float64.
        # x has dtype float32, regardless of the value of floatX
        x = theano.tensor.fscalar('x')
        y = x * 2
        z = theano.tensor.lscalar('z')

        c = y + z
        dc_dx, dc_dy, dc_dz, dc_dc = theano.grad(c, [x, y, z, c])
        # The dtype of dc_dy and dc_dz can be either float32 or float64,
        # that might depend on floatX, but is not specified.
        assert dc_dc.dtype in ('float32', 'float64')
        assert dc_dz.dtype in ('float32', 'float64')
        assert dc_dy.dtype in ('float32', 'float64')

        # When the output gradient of y is passed to op.grad, it should
        # be downcasted to float32, so dc_dx should also be float32
        assert dc_dx.dtype == 'float32'