# Utilities¶

## Visualization¶

captum.attr.visualization.visualize_image_attr(attr, original_image=None, method='heat_map', sign='absolute_value', plt_fig_axis=None, outlier_perc=2, cmap=None, alpha_overlay=0.5, show_colorbar=False, title=None, fig_size=(6, 6), use_pyplot=True)

Visualizes attribution for a given image by normalizing attribution values of the desired sign (positive, negative, absolute value, or all) and displaying them using the desired mode in a matplotlib figure.

Parameters
• attr (numpy.array) – Numpy array corresponding to attributions to be visualized. Shape must be in the form (H, W, C), with channels as last dimension. Shape must also match that of the original image if provided.

• original_image (numpy.array, optional) – Numpy array corresponding to original image. Shape must be in the form (H, W, C), with channels as the last dimension. Image can be provided either with float values in range 0-1 or int values between 0-255. This is a necessary argument for any visualization method which utilizes the original image. Default: None

• method (string, optional) –

Chosen method for visualizing attribution. Supported options are:

1. heat_map - Display heat map of chosen attributions

2. blended_heat_map - Overlay heat map over greyscale version of original image. Parameter alpha_overlay corresponds to alpha of heat map.

3. original_image - Only display original image.

5. alpha_scaling - Sets alpha channel of each pixel to be equal to normalized attribution value.

Default: heat_map

• sign (string, optional) –

Chosen sign of attributions to visualize. Supported options are:

1. positive - Displays only positive pixel attributions.

2. absolute_value - Displays absolute value of attributions.

3. negative - Displays only negative pixel attributions.

4. all - Displays both positive and negative attribution values. This is not supported for masked_image or alpha_scaling modes, since signed information cannot be represented in these modes.

Default: absolute_value

• plt_fig_axis (tuple, optional) – Tuple of matplotlib.pyplot.figure and axis on which to visualize. If None is provided, then a new figure and axis are created. Default: None

• outlier_perc (float or int, optional) – Top attribution values which correspond to a total of outlier_perc percentage of the total attribution are set to 1 and scaling is performed using the minimum of these values. For sign=all, outliers and scale value are computed using absolute value of attributions. Default: 2

• cmap (string, optional) – String corresponding to desired colormap for heatmap visualization. This defaults to “Reds” for negative sign, “Blues” for absolute value, “Greens” for positive sign, and a spectrum from red to green for all. Note that this argument is only used for visualizations displaying heatmaps. Default: None

• alpha_overlay (float, optional) – Alpha to set for heatmap when using blended_heat_map visualization mode, which overlays the heat map over the greyscaled original image. Default: 0.5

• show_colorbar (boolean, optional) – Displays colorbar for heatmap below the visualization. If given method does not use a heatmap, then a colormap axis is created and hidden. This is necessary for appropriate alignment when visualizing multiple plots, some with colorbars and some without. Default: False

• title (string, optional) – Title string for plot. If None, no title is set. Default: None

• fig_size (tuple, optional) – Size of figure created. Default: (6,6)

• use_pyplot (boolean, optional) – If true, uses pyplot to create and show figure and displays the figure after creating. If False, uses Matplotlib object oriented API and simply returns a figure object without showing. Default: True.

Returns

• figure (matplotlib.pyplot.figure):

Figure object on which visualization is created. If plt_fig_axis argument is given, this is the same figure provided.

• axis (matplotlib.pyplot.axis):

Axis object on which visualization is created. If plt_fig_axis argument is given, this is the same axis provided.

Return type

2-element tuple of figure, axis

Examples:

>>> # ImageClassifier takes a single input tensor of images Nx3x32x32,
>>> # and returns an Nx10 tensor of class probabilities.
>>> net = ImageClassifier()
>>> # Computes integrated gradients for class 3 for a given image .
>>> attribution, delta = ig.attribute(orig_image, target=3)
>>> # Displays blended heat map visualization of computed attributions.
>>> _ = visualize_image_attr(attribution, orig_image, "blended_heat_map")

captum.attr.visualization.visualize_image_attr_multiple(attr, original_image, methods, signs, titles=None, fig_size=(8, 6), use_pyplot=True, **kwargs)

Visualizes attribution using multiple visualization methods displayed in a 1 x k grid, where k is the number of desired visualizations.

Parameters
• attr (numpy.array) – Numpy array corresponding to attributions to be visualized. Shape must be in the form (H, W, C), with channels as last dimension. Shape must also match that of the original image if provided.

• original_image (numpy.array, optional) – Numpy array corresponding to original image. Shape must be in the form (H, W, C), with channels as the last dimension. Image can be provided either with values in range 0-1 or 0-255. This is a necessary argument for any visualization method which utilizes the original image.

• methods (list of strings) – List of strings of length k, defining method for each visualization. Each method must be a valid string argument for method to visualize_image_attr.

• signs (list of strings) – List of strings of length k, defining signs for each visualization. Each sign must be a valid string argument for sign to visualize_image_attr.

• titles (list of strings, optional) – List of strings of length k, providing a title string for each plot. If None is provided, no titles are added to subplots. Default: None

• fig_size (tuple, optional) – Size of figure created. Default: (8, 6)

• use_pyplot (boolean, optional) – If true, uses pyplot to create and show figure and displays the figure after creating. If False, uses Matplotlib object oriented API and simply returns a figure object without showing. Default: True.

• **kwargs (Any, optional) – Any additional arguments which will be passed to every individual visualization. Such arguments include show_colorbar, alpha_overlay, cmap, etc.

Returns

• figure (matplotlib.pyplot.figure):

Figure object on which visualization is created. If plt_fig_axis argument is given, this is the same figure provided.

• axis (matplotlib.pyplot.axis):

Axis object on which visualization is created. If plt_fig_axis argument is given, this is the same axis provided.

Return type

2-element tuple of figure, axis

Examples:

>>> # ImageClassifier takes a single input tensor of images Nx3x32x32,
>>> # and returns an Nx10 tensor of class probabilities.
>>> net = ImageClassifier()
>>> # Computes integrated gradients for class 3 for a given image .
>>> attribution, delta = ig.attribute(orig_image, target=3)
>>> # Displays original image and heat map visualization of
>>> # computed attributions side by side.
>>>                     ["original_image", "heat_map"], ["all", "positive"])


## Interpretable Embeddings¶

class captum.attr.InterpretableEmbeddingBase(embedding, full_name)[source]

Since some embedding vectors, e.g. word are created and assigned in the embedding layers of Pytorch models we need a way to access those layers, generate the embeddings and subtract the baseline. To do so, we separate embedding layers from the model, compute the embeddings separately and do all operations needed outside of the model. The original embedding layer is being replaced by InterpretableEmbeddingBase layer which passes already precomputed embedding vectors to the layers below.

Initializes internal Module state, shared by both nn.Module and ScriptModule.

forward(*inputs, **kwargs)[source]

The forward function of a wrapper embedding layer that takes and returns embedding layer. It allows embeddings to be created outside of the model and passes them seamlessly to the preceding layers of the model.

Parameters
• *inputs (Any, optional) – A sequence of inputs arguments that the forward function takes. Since forward functions can take any type and number of arguments, this will ensure that we can execute the forward pass using interpretable embedding layer. Note that if inputs are specified, it is assumed that the first argument is the embedding tensor generated using the self.embedding layer using all input arguments provided in inputs and kwargs.

• **kwargs (Any, optional) – Similar to inputs we want to make sure that our forward pass supports arbitrary number and type of key-value arguments. If inputs is not provided, kwargs must be provided and the first argument corresponds to the embedding tensor generated using the self.embedding. Note that we make here an assumption here that kwargs is an ordered dict which is new in python 3.6 and is not guaranteed that it will consistently remain that way in the newer versions. In case current implementation doesn’t work for special use cases, it is encouraged to override InterpretableEmbeddingBase and address those specifics in descendant classes.

Returns

Returns a tensor which is the same as first argument passed to the forward function. It passes pre-computed embedding tensors to lower layers without any modifications.

Return type

embedding_tensor (Tensor)

indices_to_embeddings(*input, **kwargs)[source]

Maps indices to corresponding embedding vectors. E.g. word embeddings

Parameters
• *input (Any, Optional) – This can be a tensor(s) of input indices or any other variable necessary to comput the embeddings. A typical example of input indices are word or token indices.

• **kwargs (Any, optional) – Similar to input this can be any sequence of key-value arguments necessary to compute final embedding tensor.

Returns

A tensor of word embeddings corresponding to the indices specified in the input

Return type

tensor

captum.attr.configure_interpretable_embedding_layer(model, embedding_layer_name='embedding')[source]

This method wraps model’s embedding layer with an interpretable embedding layer that allows us to access the embeddings through their indices.

Parameters
• model (torch.nn.Model) – An instance of PyTorch model that contains embeddings.

• embedding_layer_name (str, optional) – The name of the embedding layer in the model that we would like to make interpretable.

Returns

An instance of InterpretableEmbeddingBase

embedding layer that wraps model’s embedding layer that is being accessed through embedding_layer_name.

Return type

interpretable_emb (tensor)

Examples:

>>> # Let's assume that we have a DocumentClassifier model that
>>> # has a word embedding layer named 'embedding'.
>>> # To make that layer interpretable we need to execute the
>>> # following command:
>>> net = DocumentClassifier()
>>> interpretable_emb = configure_interpretable_embedding_layer(net,
>>>    'embedding')
>>> # then we can use interpretable embedding to convert our
>>> # word indices into embeddings.
>>> # Let's assume that we have the following word indices
>>> input_indices = torch.tensor([1, 0, 2])
>>> # we can access word embeddings for those indices with the command
>>> # line stated below.
>>> input_emb = interpretable_emb.indices_to_embeddings(input_indices)
>>> # Let's assume that we want to apply integrated gradients to
>>> # our model and that target attribution class is 3
>>> # after we finish the interpretation we need to remove
>>> # interpretable embedding layer with the following command:
>>> remove_interpretable_embedding_layer(net, interpretable_emb)

captum.attr.remove_interpretable_embedding_layer(model, interpretable_emb)[source]

Removes interpretable embedding layer and sets back original embedding layer in the model.

Parameters
• model (torch.nn.Module) – An instance of PyTorch model that contains embeddings

• interpretable_emb (tensor) – An instance of InterpretableEmbeddingBase that was originally created in configure_interpretable_embedding_layer function and has to be removed after interpretation is finished.

Examples:

>>> # Let's assume that we have a DocumentClassifier model that
>>> # has a word embedding layer named 'embedding'.
>>> # To make that layer interpretable we need to execute the
>>> # following command:
>>> net = DocumentClassifier()
>>> interpretable_emb = configure_interpretable_embedding_layer(net,
>>>    'embedding')
>>> # then we can use interpretable embedding to convert our
>>> # word indices into embeddings.
>>> # Let's assume that we have the following word indices
>>> input_indices = torch.tensor([1, 0, 2])
>>> # we can access word embeddings for those indices with the command
>>> # line stated below.
>>> input_emb = interpretable_emb.indices_to_embeddings(input_indices)
>>> # Let's assume that we want to apply integrated gradients to
>>> # our model and that target attribution class is 3
>>> # after we finish the interpretation we need to remove
>>> # interpretable embedding layer with the following command:
>>> remove_interpretable_embedding_layer(net, interpretable_emb)


## Token Reference Base¶

class captum.attr.TokenReferenceBase(reference_token_idx=0)[source]

A base class for creating reference (aka baseline) tensor for a sequence of tokens. A typical example of such token is PAD. Users need to provide the index of the reference token in the vocabulary as an argument to TokenReferenceBase class.

generate_reference(sequence_length, device)[source]

Generated reference tensor of given sequence_length using reference_token_idx.

Parameters
• sequence_length (int) – The length of the reference sequence

• device (torch.device) – The device on which the reference tensor will be created.

Returns

A sequence of reference token with shape:

[sequence_length]

Return type

tensor

## Linear Models¶

class captum._utils.models.model.Model[source]

Abstract Class to describe the interface of a trainable model to be used within the algorithms of captum.

Please note that this is an experimental feature.

abstract fit(train_data, **kwargs)[source]

Override this method to actually train your model.

The specification of the dataloader will be supplied by the algorithm you are using within captum. This will likely be a supervised learning task, thus you should expect batched (x, y) pairs or (x, y, w) triples.

Parameters

train_data (DataLoader) – The data to train on

Return type
Returns

Optional statistics about training, e.g. iterations it took to train, training loss, etc.

abstract representation()[source]

Returns the underlying representation of the interpretable model. For a linear model this is simply a tensor (the concatenation of weights and bias). For something slightly more complicated, such as a decision tree, this could be the nodes of a decision tree.

Return type

Tensor

Returns

A Tensor describing the representation of the model.

class captum._utils.models.linear_model.SkLearnLinearModel(sklearn_module, **kwargs)[source]

Factory class to construct a LinearModel with sklearn training method.

1. You have sklearn and numpy installed

2. The dataset can fit into memory

SkLearn support does introduce some slight overhead as we convert the tensors to numpy and then convert the resulting trained model to a LinearModel object. However, this conversion should be negligible.

Parameters
• sklearn_module (str) –

The module under sklearn to construct and use for training, e.g. use “svm.LinearSVC” for an SVM or “linear_model.Lasso” for Lasso.

There are factory classes defined for you for common use cases, such as SkLearnLasso.

• kwargs – The kwargs to pass to the construction of the sklearn model

fit(train_data, **kwargs)[source]
Parameters
• train_data (DataLoader) – Train data to use

• kwargs – Arguments to feed to .fit method for sklearn

class captum._utils.models.linear_model.SkLearnLinearRegression(**kwargs)[source]

Factory class. Trains a model with sklearn.linear_model.LinearRegression.

Any arguments provided to the sklearn constructor can be provided as kwargs here.

fit(train_data, **kwargs)[source]
Parameters
• train_data (DataLoader) – Train data to use

• kwargs – Arguments to feed to .fit method for sklearn

class captum._utils.models.linear_model.SkLearnLasso(**kwargs)[source]

Factory class. Trains a LinearModel model with sklearn.linear_model.Lasso. You will need sklearn version >= 0.23 to support sample weights.

fit(train_data, **kwargs)[source]
Parameters
• train_data (DataLoader) – Train data to use

• kwargs – Arguments to feed to .fit method for sklearn

class captum._utils.models.linear_model.SkLearnRidge(**kwargs)[source]

Factory class. Trains a model with sklearn.linear_model.Ridge.

Any arguments provided to the sklearn constructor can be provided as kwargs here.

fit(train_data, **kwargs)[source]
Parameters
• train_data (DataLoader) – Train data to use

• kwargs – Arguments to feed to .fit method for sklearn

class captum._utils.models.linear_model.SGDLinearModel(**kwargs)[source]

Factory class. Construct a a LinearModel with the sgd_train_linear_model as the train method

Parameters

kwargs – Arguments send to self._construct_model_params after self.fit is called. Please refer to that method for parameter documentation.

class captum._utils.models.linear_model.SGDLasso(**kwargs)[source]

Factory class to train a LinearModel with SGD (sgd_train_linear_model) whilst setting appropriate parameters to optimize for ridge regression loss. This optimizes L2 loss + alpha * L1 regularization.

Please note that with SGD it is not guaranteed that weights will converge to 0.

fit(train_data, **kwargs)[source]

Calls self.train_fn

class captum._utils.models.linear_model.SGDRidge(**kwargs)[source]

Factory class to train a LinearModel with SGD (sgd_train_linear_model) whilst setting appropriate parameters to optimize for ridge regression loss. This optimizes L2 loss + alpha * L2 regularization.

fit(train_data, **kwargs)[source]

Calls self.train_fn