# tf.contrib.eager.gradients_function

tf.contrib.eager.gradients_function(
f,
params=None
)


Returns a function which differentiates f with respect to params.

Example:

# f(x, y) = (x ^ 3) * y - x * (y ^ 2)
# Therefore, the 1st order derivatives are:
#   df / dx = 3 * (x ^ 2) * y - y ^ 2
#   df / dy = x ^ 3 - 2 * x * y
# The 2nd order derivatives with respect to x is:
#   d^2 f / (dx)^2 = 6 * x * y
def f(x, y):
return x * x * x * y - x * y * y

# Obtain a function that returns 1st order gradients.
grad_fn = tfe.gradients_function(f)

x = 2.0
y = 3.0

# Invoke the 1st order gradient function.
x_grad, y_grad = grad_fn(x, y)
assert x_grad.numpy() == 3 * (2 ** 2) * 3 - 3 ** 2
assert y_grad.numpy() == (2 ** 3) - 2 * 2 * 3

# Obtain a function that returns the 2nd order gradient with respect to x.
gradgrad_fn = tfe.gradients_function(lambda x, y: grad_fn(x, y)[0])

# Invoke the 2nd order gradient function.
x_gradgrad = gradgrad_fn(x, y)[0]
assert x_gradgrad.numpy() == 6 * 2 * 3

# To obtain a callable that returns the gradient(s) of f with respect to a
# subset of its inputs, use the params keyword argument with
# gradients_function().
ygrad_fn = tfe.gradients_function(f, params=[1])

(y_grad,) = ygrad_fn(x, y)
assert y_grad.numpy() == (2 ** 3) - 2 * 2 * 3


#### Args:

f: function to be differentiated. If f returns a scalar, this scalar will be differentiated. If f returns a tensor or list of tensors, by default a scalar will be computed by adding all their values to produce a single scalar. If desired, the tensors can be elementwise multiplied by the tensors passed as the dy keyword argument to the returned gradient function. params: list of parameter names of f or list of integers indexing the parameters with respect to which we'll differentiate. Passing None differentiates with respect to all parameters.

#### Returns:

function which, when called, returns the value of f and the gradient of f with respect to all of params. The function takes an extra optional keyword argument "dy". Setting it allows computation of vector jacobian products for vectors other than the vector of ones.

#### Raises:

ValueError: if the params are not all strings or all integers.