Checks whether adding more features to a baseline explanation monotonically increases the model output (Sundararajan & Najmi, 2020). Returns the fraction of features that satisfy this property. ↑ better.
monotonicity
monotonicity(
forward_func: Callable,
inputs: TensorOrTupleOfTensorsGeneric,
attributions: list[TensorOrTupleOfTensorsGeneric] | TensorOrTupleOfTensorsGeneric,
baselines: BaselineType,
feature_mask: TensorOrTupleOfTensorsGeneric | None = None,
additional_forward_args: Any = None,
target: ExplanationTarget | list[ExplanationTarget] = NoTarget(),
frozen_features: list[Tensor] | None = None,
max_features_processed_per_batch: int | None = None,
percentage_feature_removal_per_step: float = 0.01,
multi_target: bool = False,
show_progress: bool = True,
return_intermediate_results: bool = False,
return_dict: bool = False,
) -> tuple | dict | Tensor | list[Tensor]
Implementation of Monotonicity metric by Arya at el., 2019. This implementation reuses the batch-computation ideas from captum and therefore it is fully compatible with the Captum library. In addition, the implementation takes some ideas about the implementation of the metric from the python Quantus library.
Monotonicity tests if adding more positive evidence increases the probability of classification in the specified class.
It captures attributions' faithfulness by incrementally adding each attribute in order of increasing importance and evaluating the effect on model performance. As more features are added, the performance of the model is expected to increase and thus result in monotonically increasing model performance.
References
1) Vijay Arya et al.: "One explanation does not fit all: A toolkit and taxonomy of ai explainability techniques." arXiv preprint arXiv:1909.03012 (2019). 2) Ronny Luss et al.: "Generating contrastive explanations with monotonic attribute functions." arXiv preprint arXiv:1905.12698 (2019).
Parameters:
-
(forward_funcCallable) –The forward function of the model or any modification of it. -
(inputsTensor 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 (aka batch size), and if multiple input tensors are provided, the examples must be aligned appropriately.
-
(baselinesscalar, Tensor, tuple of scalar, or Tensor) –Baselines define reference values against which the completeness is measured which sometimes represent ablated values and are used to compare with the actual inputs to compute importance scores in attribution algorithms. They can be represented as: - a single tensor, if inputs is a single tensor, with exactly the same dimensions as inputs or the first dimension is one and the remaining dimensions match with inputs. - a single scalar, if inputs is a single tensor, which will be broadcasted for each input value in input tensor. - a tuple of tensors or scalars, the baseline corresponding to each tensor in the inputs' tuple can be: - either a tensor with matching dimensions to corresponding tensor in the inputs' tuple or the first dimension is one and the remaining dimensions match with the corresponding input tensor. - or a scalar, corresponding to a tensor in the inputs' tuple. This scalar value is broadcasted for corresponding input tensor. Default: None -
(attributionsTensor or tuple[Tensor, ...]) –Attribution scores computed based on an attribution algorithm. This attribution scores can be computed using the implementations provided in the `captum.attr` package. Some of those attribution approaches are so called global methods, which means that they factor in model inputs' multiplier, as described in: https://arxiv.org/abs/1711.06104 Many global attribution algorithms can be used in local modes, meaning that the inputs multiplier isn't factored in the attribution scores. This can be done duing the definition of the attribution algorithm by passing `multipy_by_inputs=False` flag. For example in case of Integrated Gradients (IG) we can obtain local attribution scores if we define the constructor of IG as: ig = IntegratedGradients(multipy_by_inputs=False) Some attribution algorithms are inherently local. Examples of inherently local attribution methods include: Saliency, Guided GradCam, Guided Backprop and Deconvolution. For local attributions we can use real-valued perturbations whereas for global attributions that perturbation is binary. https://arxiv.org/abs/1901.09392 If we want to compute the infidelity of global attributions we can use a binary perturbation matrix that will allow us to select a subset of features from `inputs` or `inputs - baselines` space. This will allow us to approximate sensitivity-n for a global attribution algorithm. Attributions have the same shape and dimensionality as the inputs. If inputs is a single tensor then the attributions is a single tensor as well. If inputs is provided as a tuple of tensors then attributions will be tuples of tensors as well. -
(feature_maskTensor or tuple[Tensor, ...], default:None) –feature_mask defines a mask for the input, grouping features which should be perturbed together. feature_mask should contain the same number of tensors as inputs. Each tensor should be the same size as the corresponding input or broadcastable to match the input tensor. Each tensor should contain integers in the range 0 to num_features - 1, and indices corresponding to the same feature should have the same value. Note that features within each input tensor are perturbed independently (not across tensors). If the forward function returns a single scalar per batch, we enforce that the first dimension of each mask must be 1, since attributions are returned batch-wise rather than per example, so the attributions must correspond to the same features (indices) in each input example. If None, then a feature mask is constructed which assigns each scalar within a tensor as a separate feature, which is perturbed independently. Default: None -
(additional_forward_argsAny, default:None) –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 the perturbations are not computed with respect to these arguments.
Default: None -
(targetint, tuple, Tensor, or list, default:NoTarget()) –Indices for selecting predictions from output(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 -
(max_features_processed_per_batchint, default:None) –The number of maximum input features that are processed together for every example. In case the number of features to be perturbed in each example (
total_features_perturbed) exceedsmax_features_processed_per_batch, they will be sliced into batches ofmax_features_processed_per_batchexamples and processed in a sequential order. -
(percentage_feature_removal_per_stepint, default:0.01) –The number of steps to process the features in a single batch. This is useful for reducing the computation time for large models. This allows 'percentage_feature_removal_per_step' ascending features to be removed together in each step instead of removing all the features. Therefore, if percentage_feature_removal_per_step=10, instead of removing the features X1, <X2, <X3... in each step, we will remove the features <X1-10, <X10-X20, <X20-X30 ... Default: 1
-
(frozen_featuresList[Tensor], default:None) –A list of frozen features that are not perturbed. This can be useful for ignoring the input structure features like padding, etc. Default: None In case CLS,PAD,SEP tokens are present in the input, they can be frozen by passing the indices of feature masks that correspond to these tokens.
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(multi_targetbool, default:False) –A boolean flag that indicates whether the metric computation is for multi-target explanations. if set to true, the targets are required to be a list of integers each corresponding to a required target class in the output. The corresponding metric outputs are then returned as a list of metric outputs corresponding to each target class. Default is False.
-
(show_progressbool, default:True) –Displays the progress of computation.
-
(return_intermediate_resultsbool, default:False) –A boolean flag that indicates whether the intermediate results of the metric computation are returned. If set to True, the intermediate results are returned as a tuple of tensors. Default is False.
-
(return_dictbool, default:False) –A boolean flag that indicates whether the metric outputs are returned as a dictionary with keys as the metric names and values as the corresponding metric outputs. Default is False.
Returns: Returns: A tuple of three tensors: Tensor: - The monotonicity scores of the batch. The first dimension is equal to the number of examples in the input batch and the second dimension is 1. Tensor: - The forward outputs when features are slowly added to baseline for monotonicity computation. Examples:: >>> # ImageClassifier takes a single input tensor of images Nx3x32x32, >>> # and returns an Nx10 tensor of class probabilities. >>> net = ImageClassifier() >>> saliency = Saliency(net) >>> input = torch.randn(2, 3, 32, 32, requires_grad=True) >>> baselines = torch.zeros(2, 3, 32, 32) >>> # Computes saliency maps for class 3. >>> attribution = saliency.attribute(input, target=3) >>> # define a perturbation function for the input
>>> # Computes the monotonicity scores for saliency maps
>>> monotonicity, asc_baseline_perturb_fwds = monotonicity(net, input, attribution, baselines)
Source code in torchxai/metrics/faithfulness/monotonicity.py
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