# Source code for captum.attr._core.layer.layer_gradient_x_activation

```
#!/usr/bin/env python3
from typing import Any, Callable, List, Tuple, Union
from captum._utils.common import (
_format_additional_forward_args,
_format_output,
_format_tensor_into_tuples,
)
from captum._utils.gradient import compute_layer_gradients_and_eval
from captum._utils.typing import ModuleOrModuleList, TargetType
from captum.attr._utils.attribution import GradientAttribution, LayerAttribution
from captum.log import log_usage
from torch import Tensor
from torch.nn import Module
[docs]
class LayerGradientXActivation(LayerAttribution, GradientAttribution):
r"""
Computes element-wise product of gradient and activation for selected
layer on given inputs.
"""
def __init__(
self,
forward_func: Callable,
layer: ModuleOrModuleList,
device_ids: Union[None, List[int]] = None,
multiply_by_inputs: bool = True,
) -> None:
r"""
Args:
forward_func (Callable): The forward function of the model or any
modification of it
layer (torch.nn.Module or list of torch.nn.Module): Layer or layers
for which attributions are computed.
Output size of attribute matches this layer's input or
output dimensions, depending on whether we attribute to
the inputs or outputs of the layer, corresponding to
attribution of each neuron in the input or output of
this layer. If multiple layers are provided, attributions
are returned as a list, each element corresponding to the
attributions of the corresponding layer.
device_ids (list[int]): Device ID list, necessary only if forward_func
applies a DataParallel model. This allows reconstruction of
intermediate outputs from batched results across devices.
If forward_func is given as the DataParallel model itself,
then it is not necessary to provide this argument.
multiply_by_inputs (bool, optional): Indicates whether to factor
model inputs' multiplier in the final attribution scores.
In the literature this is also known as local vs global
attribution. If inputs' multiplier isn't factored in,
then this type of attribution method is also called local
attribution. If it is, then that type of attribution
method is called global.
More detailed can be found here:
https://arxiv.org/abs/1711.06104
In case of layer gradient x activation, if `multiply_by_inputs`
is set to True, final sensitivity scores are being multiplied by
layer activations for inputs.
"""
LayerAttribution.__init__(self, forward_func, layer, device_ids)
GradientAttribution.__init__(self, forward_func)
self._multiply_by_inputs = multiply_by_inputs
@property
def multiplies_by_inputs(self):
return self._multiply_by_inputs
[docs]
@log_usage()
def attribute(
self,
inputs: Union[Tensor, Tuple[Tensor, ...]],
target: TargetType = None,
additional_forward_args: Any = None,
attribute_to_layer_input: bool = False,
) -> Union[Tensor, Tuple[Tensor, ...], List[Union[Tensor, Tuple[Tensor, ...]]]]:
r"""
Args:
inputs (Tensor or tuple[Tensor, ...]): Input for which attributions
are computed. If forward_func takes a single
tensor as input, a single input tensor should be provided.
If forward_func takes multiple tensors as input, a tuple
of the input tensors should be provided. It is assumed
that for all given input tensors, dimension 0 corresponds
to the number of examples, and if multiple input tensors
are provided, the examples must be aligned appropriately.
target (int, tuple, Tensor, or list, optional): Output indices for
which gradients are computed (for classification cases,
this is usually the target class).
If the network returns a scalar value per example,
no target index is necessary.
For general 2D outputs, targets can be either:
- a single integer or a tensor containing a single
integer, which is applied to all input examples
- a list of integers or a 1D tensor, with length matching
the number of examples in inputs (dim 0). Each integer
is applied as the target for the corresponding example.
For outputs with > 2 dimensions, targets can be either:
- A single tuple, which contains #output_dims - 1
elements. This target index is applied to all examples.
- A list of tuples with length equal to the number of
examples in inputs (dim 0), and each tuple containing
#output_dims - 1 elements. Each tuple is applied as the
target for the corresponding example.
Default: None
additional_forward_args (Any, optional): If the forward function
requires additional arguments other than the inputs for
which attributions should not be computed, this argument
can be provided. It must be either a single additional
argument of a Tensor or arbitrary (non-tuple) type or a
tuple containing multiple additional arguments including
tensors or any arbitrary python types. These arguments
are provided to forward_func in order following the
arguments in inputs.
Note that attributions are not computed with respect
to these arguments.
Default: None
attribute_to_layer_input (bool, optional): Indicates whether to
compute the attribution with respect to the layer input
or output. If `attribute_to_layer_input` is set to True
then the attributions will be computed with respect to
layer input, otherwise it will be computed with respect
to layer output.
Default: False
Returns:
*Tensor* or *tuple[Tensor, ...]* or list of **attributions**:
- **attributions** (*Tensor*, *tuple[Tensor, ...]*, or *list*):
Product of gradient and activation for each
neuron in given layer output.
Attributions will always be the same size as the
output of the given layer.
Attributions are returned in a tuple if
the layer inputs / outputs contain multiple tensors,
otherwise a single tensor is returned.
If multiple layers are provided, attributions
are returned as a list, each element corresponding to the
activations of the corresponding layer.
Examples::
>>> # ImageClassifier takes a single input tensor of images Nx3x32x32,
>>> # and returns an Nx10 tensor of class probabilities.
>>> # It contains an attribute conv1, which is an instance of nn.conv2d,
>>> # and the output of this layer has dimensions Nx12x32x32.
>>> net = ImageClassifier()
>>> layer_ga = LayerGradientXActivation(net, net.conv1)
>>> input = torch.randn(2, 3, 32, 32, requires_grad=True)
>>> # Computes layer activation x gradient for class 3.
>>> # attribution size matches layer output, Nx12x32x32
>>> attribution = layer_ga.attribute(input, 3)
"""
inputs = _format_tensor_into_tuples(inputs)
additional_forward_args = _format_additional_forward_args(
additional_forward_args
)
# Returns gradient of output with respect to
# hidden layer and hidden layer evaluated at each input.
layer_gradients, layer_evals = compute_layer_gradients_and_eval(
self.forward_func,
self.layer,
inputs,
target,
additional_forward_args,
device_ids=self.device_ids,
attribute_to_layer_input=attribute_to_layer_input,
)
if isinstance(self.layer, Module):
return _format_output(
len(layer_evals) > 1,
self.multiply_gradient_acts(layer_gradients, layer_evals),
)
else:
return [
_format_output(
len(layer_evals[i]) > 1,
self.multiply_gradient_acts(layer_gradients[i], layer_evals[i]),
)
for i in range(len(self.layer))
]
def multiply_gradient_acts(
self, gradients: Tuple[Tensor, ...], evals: Tuple[Tensor, ...]
) -> Tuple[Tensor, ...]:
return tuple(
single_gradient * single_eval
if self.multiplies_by_inputs
else single_gradient
for single_gradient, single_eval in zip(gradients, evals)
)
```