vjp(func, inputs, v=None, create_graph=False, strict=False)¶
Function that computes the dot product between a vector
vand the Jacobian of the given function at the point given by the inputs.
func (function) – a Python function that takes Tensor inputs and returns a tuple of Tensors or a Tensor.
inputs (tuple of Tensors or Tensor) – inputs to the function
v (tuple of Tensors or Tensor) – The vector for which the vector Jacobian product is computed. Must be the same size as the output of
func. This argument is optional when the output of
funccontains a single element and (if it is not provided) will be set as a Tensor containing a single
create_graph (bool, optional) – If
True, both the output and result will be computed in a differentiable way. Note that when
False, the result can not require gradients or be disconnected from the inputs. Defaults to
strict (bool, optional) – If
True, an error will be raised when we detect that there exists an input such that all the outputs are independent of it. If
False, we return a Tensor of zeros as the vjp for said inputs, which is the expected mathematical value. Defaults to
- tuple with:
func_output (tuple of Tensors or Tensor): output of
vjp (tuple of Tensors or Tensor): result of the dot product with the same shape as the inputs.
- Return type
>>> def exp_reducer(x): ... return x.exp().sum(dim=1) >>> inputs = torch.rand(4, 4) >>> v = torch.ones(4) >>> vjp(exp_reducer, inputs, v) (tensor([5.7817, 7.2458, 5.7830, 6.7782]), tensor([[1.4458, 1.3962, 1.3042, 1.6354], [2.1288, 1.0652, 1.5483, 2.5035], [2.2046, 1.1292, 1.1432, 1.3059], [1.3225, 1.6652, 1.7753, 2.0152]]))
>>> vjp(exp_reducer, inputs, v, create_graph=True) (tensor([5.7817, 7.2458, 5.7830, 6.7782], grad_fn=<SumBackward1>), tensor([[1.4458, 1.3962, 1.3042, 1.6354], [2.1288, 1.0652, 1.5483, 2.5035], [2.2046, 1.1292, 1.1432, 1.3059], [1.3225, 1.6652, 1.7753, 2.0152]], grad_fn=<MulBackward0>))
>>> def adder(x, y): ... return 2 * x + 3 * y >>> inputs = (torch.rand(2), torch.rand(2)) >>> v = torch.ones(2) >>> vjp(adder, inputs, v) (tensor([2.4225, 2.3340]), (tensor([2., 2.]), tensor([3., 3.])))