Package: captum
Captum is a model interpretability and understanding library for PyTorch.
Captum means comprehension in Latin and contains general purpose implementations
of integrated gradients, saliency maps, smoothgrad, vargrad and others for
PyTorch models. It has quick integration for models built with domain-specific
libraries such as torchvision, torchtext, and others.Captum is currently in beta and under active development!About CaptumWith the increase in model complexity and the resulting lack of transparency, model interpretability methods have become increasingly important. Model understanding is both an active area of research as well as an area of focus for practical applications across industries using machine learning. Captum provides state-of-the-art algorithms such as Integrated Gradients, Testing with Concept Activaton Vectors (TCAV), TracIn influence functions, just to name a few, that provide researchers and developers with an easy way to understand which features, training examples or concepts contribute to a models' predictions and in general what and how the model learns. In addition to that, Captum also provides adversarial attacks and minimal input perturbation capabilities that can be used both for generating counterfactual explanations and adversarial perturbations.Captum helps ML researchers more easily implement interpretability algorithms that can interact with PyTorch models. Captum also allows researchers to quickly benchmark their work against other existing algorithms available in the library.Target AudienceThe primary audiences for Captum are model developers who are looking to improve their models and understand which concepts, features or training examples are important and interpretability researchers focused on identifying algorithms that can better interpret many types of models.Captum can also be used by application engineers who are using trained models in production. Captum provides easier troubleshooting through improved model interpretability, and the potential for delivering better explanations to end users on why they’re seeing a specific piece of content, such as a movie recommendation.InstallationInstallation RequirementsPython >= 3.6PyTorch >= 1.6Installing the latest releaseThe latest release of Captum is easily installed either viaAnaconda(recommended) or viapip.withcondaYou can install captum from any of the following supported conda channels:channel:pytorchcondainstallcaptum-cpytorchchannel:conda-forgecondainstallcaptum-cconda-forgeWithpippipinstallcaptumManual / Dev installIf you'd like to try our bleeding edge features (and don't mind potentially
running into the occasional bug here or there), you can install the latest
master directly from GitHub. For a basic install, run:gitclonehttps://github.com/pytorch/captum.gitcdcaptum
pipinstall-e.To customize the installation, you can also run the following variants of the
above:pip install -e .[insights]: Also installs all packages necessary for running Captum Insights.pip install -e .[dev]: Also installs all tools necessary for development
(testing, linting, docs building; seeContributingbelow).pip install -e .[tutorials]: Also installs all packages necessary for running the tutorial notebooks.To execute unit tests from a manual install, run:# running a single unit testpython-munittest-vtests.attr.test_saliency# running all unit testspytest-raGetting StartedCaptum helps you interpret and understand predictions of PyTorch models by
exploring features that contribute to a prediction the model makes.
It also helps understand which neurons and layers are important for
model predictions.Let's apply some of those algorithms to a toy model we have created for
demonstration purposes.
For simplicity, we will use the following architecture, but users are welcome
to use any PyTorch model of their choice.importnumpyasnpimporttorchimporttorch.nnasnnfromcaptum.attrimport(GradientShap,DeepLift,DeepLiftShap,IntegratedGradients,LayerConductance,NeuronConductance,NoiseTunnel,)classToyModel(nn.Module):def__init__(self):super().__init__()self.lin1=nn.Linear(3,3)self.relu=nn.ReLU()self.lin2=nn.Linear(3,2)# initialize weights and biasesself.lin1.weight=nn.Parameter(torch.arange(-4.0,5.0).view(3,3))self.lin1.bias=nn.Parameter(torch.zeros(1,3))self.lin2.weight=nn.Parameter(torch.arange(-3.0,3.0).view(2,3))self.lin2.bias=nn.Parameter(torch.ones(1,2))defforward(self,input):returnself.lin2(self.relu(self.lin1(input)))Let's create an instance of our model and set it to eval mode.model=ToyModel()model.eval()Next, we need to define simple input and baseline tensors.
Baselines belong to the input space and often carry no predictive signal.
Zero tensor can serve as a baseline for many tasks.
Some interpretability algorithms such asIntegratedGradients,DeepliftandGradientShapare designed to attribute the change
between the input and baseline to a predictive class or a value that the neural
network outputs.We will apply model interpretability algorithms on the network
mentioned above in order to understand the importance of individual
neurons/layers and the parts of the input that play an important role in the
final prediction.To make computations deterministic, let's fix random seeds.torch.manual_seed(123)np.random.seed(123)Let's define our input and baseline tensors. Baselines are used in some
interpretability algorithms such asIntegratedGradients, DeepLift, GradientShap, NeuronConductance, LayerConductance, InternalInfluenceandNeuronIntegratedGradients.input=torch.rand(2,3)baseline=torch.zeros(2,3)Next we will useIntegratedGradientsalgorithms to assign attribution
scores to each input feature with respect to the first target output.ig=IntegratedGradients(model)attributions,delta=ig.attribute(input,baseline,target=0,return_convergence_delta=True)print('IG Attributions:',attributions)print('Convergence Delta:',delta)Output:IG Attributions: tensor([[-0.5922, -1.5497, -1.0067],
                         [ 0.0000, -0.2219, -5.1991]])
Convergence Delta: tensor([2.3842e-07, -4.7684e-07])The algorithm outputs an attribution score for each input element and a
convergence delta. The lower the absolute value of the convergence delta the better
is the approximation. If we choose not to return delta,
we can simply not provide thereturn_convergence_deltainput
argument. The absolute value of the returned deltas can be interpreted as an
approximation error for each input sample.
It can also serve as a proxy of how accurate the integral approximation for given
inputs and baselines is.
If the approximation error is large, we can try a larger number of integral
approximation steps by settingn_stepsto a larger value. Not all algorithms
return approximation error. Those which do, though, compute it based on the
completeness property of the algorithms.Positive attribution score means that the input in that particular position
positively contributed to the final prediction and negative means the opposite.
The magnitude of the attribution score signifies the strength of the contribution.
Zero attribution score means no contribution from that particular feature.Similarly, we can applyGradientShap,DeepLiftand other attribution algorithms to the model.GradientShapfirst chooses a random baseline from baselines' distribution, then
adds gaussian noise with std=0.09 to each input examplen_samplestimes.
Afterwards, it chooses a random point between each example-baseline pair and
computes the gradients with respect to target class (in this case target=0). Resulting
attribution is the mean of gradients * (inputs - baselines)gs=GradientShap(model)# We define a distribution of baselines and draw `n_samples` from that# distribution in order to estimate the expectations of gradients across all baselinesbaseline_dist=torch.randn(10,3)*0.001attributions,delta=gs.attribute(input,stdevs=0.09,n_samples=4,baselines=baseline_dist,target=0,return_convergence_delta=True)print('GradientShap Attributions:',attributions)print('Convergence Delta:',delta)OutputGradientShap Attributions: tensor([[-0.1542, -1.6229, -1.5835],
                                   [-0.3916, -0.2836, -4.6851]])
Convergence Delta: tensor([ 0.0000, -0.0005, -0.0029, -0.0084, -0.0087, -0.0405,  0.0000, -0.0084])Deltas are computed for eachn_samples * input.shape[0]example. The user can,
for instance, average them:deltas_per_example=torch.mean(delta.reshape(input.shape[0],-1),dim=1)in order to get per example average delta.Below is an example of how we can applyDeepLiftandDeepLiftShapon theToyModeldescribed above. The current implementation of DeepLift supports only theRescalerule.
For more details on alternative implementations, please see theDeepLift paper.dl=DeepLift(model)attributions,delta=dl.attribute(input,baseline,target=0,return_convergence_delta=True)print('DeepLift Attributions:',attributions)print('Convergence Delta:',delta)OutputDeepLift Attributions: tensor([[-0.5922, -1.5497, -1.0067],
                               [ 0.0000, -0.2219, -5.1991])
Convergence Delta: tensor([0., 0.])DeepLiftassigns similar attribution scores asIntegratedGradientsto inputs,
however it has lower execution time. Another important thing to remember about
DeepLift is that it currently doesn't support all non-linear activation types.
For more details on limitations of the current implementation, please see theDeepLift paper.Similar to integrated gradients, DeepLift returns a convergence delta score
per input example. The approximation error is then the absolute
value of the convergence deltas and can serve as a proxy of how accurate the
algorithm's approximation is.Now let's look intoDeepLiftShap. Similar toGradientShap,DeepLiftShapuses
baseline distribution. In the example below, we use the same baseline distribution
as forGradientShap.dl=DeepLiftShap(model)attributions,delta=dl.attribute(input,baseline_dist,target=0,return_convergence_delta=True)print('DeepLiftSHAP Attributions:',attributions)print('Convergence Delta:',delta)OutputDeepLiftShap Attributions: tensor([[-5.9169e-01, -1.5491e+00, -1.0076e+00],
                                   [-4.7101e-03, -2.2300e-01, -5.1926e+00]], grad_fn=<MeanBackward1>)
Convergence Delta: tensor([-4.6120e-03, -1.6267e-03, -5.1045e-04, -1.4184e-03, -6.8886e-03,
                           -2.2224e-02,  0.0000e+00, -2.8790e-02, -4.1285e-03, -2.7295e-02,
                           -3.2349e-03, -1.6265e-03, -4.7684e-07, -1.4191e-03, -6.8889e-03,
                           -2.2224e-02,  0.0000e+00, -2.4792e-02, -4.1289e-03, -2.7296e-02])DeepLiftShapusesDeepLiftto compute attribution score for each
input-baseline pair and averages it for each input across all baselines.It computes deltas for each input example-baseline pair, thus resulting toinput.shape[0] * baseline.shape[0]delta values.Similar to GradientShap in order to compute example-based deltas we can average them per example:deltas_per_example=torch.mean(delta.reshape(input.shape[0],-1),dim=1)In order to smooth and improve the quality of the attributions we can runIntegratedGradientsand other attribution methods through aNoiseTunnel.NoiseTunnelallows us to useSmoothGrad,SmoothGrad_SqandVarGradtechniques
to smoothen the attributions by aggregating them for multiple noisy
samples that were generated by adding gaussian noise.Here is an example of how we can useNoiseTunnelwithIntegratedGradients.ig=IntegratedGradients(model)nt=NoiseTunnel(ig)attributions,delta=nt.attribute(input,nt_type='smoothgrad',stdevs=0.02,nt_samples=4,baselines=baseline,target=0,return_convergence_delta=True)print('IG + SmoothGrad Attributions:',attributions)print('Convergence Delta:',delta)OutputIG + SmoothGrad Attributions: tensor([[-0.4574, -1.5493, -1.0893],
                                      [ 0.0000, -0.2647, -5.1619]])
Convergence Delta: tensor([ 0.0000e+00,  2.3842e-07,  0.0000e+00, -2.3842e-07,  0.0000e+00,
        -4.7684e-07,  0.0000e+00, -4.7684e-07])The number of elements in thedeltatensor is equal to:nt_samples * input.shape[0]In order to get an example-wise delta, we can, for example, average them:deltas_per_example=torch.mean(delta.reshape(input.shape[0],-1),dim=1)Let's look into the internals of our network and understand which layers
and neurons are important for the predictions.We will start with theNeuronConductance.NeuronConductancehelps us to identify
input features that are important for a particular neuron in a given
layer. It decomposes the computation of integrated gradients via the chain rule by
defining the importance of a neuron as path integral of the derivative of the output
with respect to the neuron times the derivatives of the neuron with respect to the
inputs of the model.In this case, we choose to analyze the first neuron in the linear layer.nc=NeuronConductance(model,model.lin1)attributions=nc.attribute(input,neuron_selector=1,target=0)print('Neuron Attributions:',attributions)OutputNeuron Attributions: tensor([[ 0.0000,  0.0000,  0.0000],
                             [ 1.3358,  0.0000, -1.6811]])Layer conductance shows the importance of neurons for a layer and given input.
It is an extension of path integrated gradients for hidden layers and holds the
completeness property as well.It doesn't attribute the contribution scores to the input features
but shows the importance of each neuron in the selected layer.lc=LayerConductance(model,model.lin1)attributions,delta=lc.attribute(input,baselines=baseline,target=0,return_convergence_delta=True)print('Layer Attributions:',attributions)print('Convergence Delta:',delta)OutputsLayer Attributions: tensor([[ 0.0000,  0.0000, -3.0856],
                            [ 0.0000, -0.3488, -4.9638]], grad_fn=<SumBackward1>)
Convergence Delta: tensor([0.0630, 0.1084])Similar to other attribution algorithms that return convergence delta,LayerConductancereturns the deltas for each example. The approximation error is then the absolute
value of the convergence deltas and can serve as a proxy of how accurate integral
approximation for given inputs and baselines is.More details on the list of supported algorithms and how to apply
Captum on different types of models can be found in our tutorials.Captum InsightsCaptum provides a web interface called Insights for easy visualization and
access to a number of our interpretability algorithms.To analyze a sample model on CIFAR10 via Captum Insights runpython -m captum.insights.exampleand navigate to the URL specified in the output.To build Insights you will needNode>= 8.x
andYarn>= 1.5.To build and launch from a checkout in a conda environment runconda install -c conda-forge yarn
BUILD_INSIGHTS=1 python setup.py develop
python captum/insights/example.pyCaptum Insights Jupyter WidgetCaptum Insights also has a Jupyter widget providing the same user interface as the web app.
To install and enable the widget, runjupyter nbextension install --py --symlink --sys-prefix captum.insights.attr_vis.widget
jupyter nbextension enable captum.insights.attr_vis.widget --py --sys-prefixTo build the widget from a checkout in a conda environment runconda install -c conda-forge yarn
BUILD_INSIGHTS=1 python setup.py developFAQIf you have questions about using Captum methods, please check thisFAQ, which addresses many common issues.ContributingSee theCONTRIBUTINGfile for how to help out.Talks and PapersNeurIPS 2019:The slides of our presentation  can be foundhereKDD 2020:The slides of our presentation from KDD 2020 tutorial can be foundhere.
You can watch the recorded talkhereGTC 2020:Opening Up the Black Box: Model Understanding with Captum and PyTorch.
You can watch the recorded talkhereXAI Summit 2020:Using Captum and Fiddler to Improve Model Understanding with Explainable AI.
You can watch the recorded talkherePyTorch Developer Day 2020Model Interpretability.
You can watch the recorded talkhereNAACL 2021Tutorial on Fine-grained Interpretation and Causation Analysis in Deep NLP Models.
You can watch the recorded talkhereICLR 2021 workshop on Responsible AI:Paperon the Captum LibraryPaperon Invesitgating Sanity Checks for Saliency MapsSummer school on medical imaging at University of Lyon. A class on model explainability (link to the video)https://www.youtube.com/watch?v=vn-jLzY67V0References of AlgorithmsIntegratedGradients,LayerIntegratedGradients:Axiomatic Attribution for Deep Networks, Mukund Sundararajan et al. 2017andDid the Model Understand the Question?, Pramod K. Mudrakarta, et al. 2018InputXGradient:Not Just a Black Box: Learning Important Features Through Propagating Activation Differences, Avanti Shrikumar et al. 2016SmoothGrad:SmoothGrad: removing noise by adding noise, Daniel Smilkov et al. 2017NoiseTunnel:Sanity Checks for Saliency Maps, Julius Adebayo et al. 2018NeuronConductance:How Important is a neuron?, Kedar Dhamdhere et al. 2018LayerConductance:Computationally Efficient Measures of Internal Neuron Importance, Avanti Shrikumar et al. 2018DeepLift,NeuronDeepLift,LayerDeepLift:Learning Important Features Through Propagating Activation Differences, Avanti Shrikumar et al. 2017andTowards better understanding of gradient-based attribution methods for deep neural networks, Marco Ancona et al. 2018NeuronIntegratedGradients:Computationally Efficient Measures of Internal Neuron Importance, Avanti Shrikumar et al. 2018GradientShap,NeuronGradientShap,LayerGradientShap,DeepLiftShap,NeuronDeepLiftShap,LayerDeepLiftShap:A Unified Approach to Interpreting Model Predictions, Scott M. Lundberg et al. 2017InternalInfluence:Influence-Directed Explanations for Deep Convolutional Networks, Klas Leino et al. 2018Saliency,NeuronGradient:Deep Inside Convolutional Networks: Visualising
Image Classification Models and Saliency Maps, K. Simonyan, et. al. 2014GradCAM,Guided GradCAM:Grad-CAM: Visual Explanations from Deep Networks via Gradient-based Localization, Ramprasaath R. Selvaraju et al. 2017Deconvolution,Neuron Deconvolution:Visualizing and Understanding Convolutional Networks, Matthew D Zeiler et al. 2014Guided Backpropagation,Neuron Guided Backpropagation:Striving for Simplicity: The All Convolutional Net, Jost Tobias Springenberg et al. 2015Feature Permutation:Permutation Feature ImportanceOcclusion:Visualizing and Understanding Convolutional NetworksShapley Value:A value for n-person games. Contributions to the Theory of Games 2.28 (1953): 307-317Shapley Value Sampling:Polynomial calculation of the Shapley value based on samplingInfidelity and Sensitivity:On the (In)fidelity and Sensitivity for ExplanationsTracInCP, TracInCPFast, TracInCPRandProj:Estimating Training Data Influence by Tracing Gradient DescentSimilarityInfluence: [Pairwise similarities between train and test examples based on predefined similarity metrics]BinaryConcreteStochasticGates:Stochastic Gates with Binary Concrete DistributionGaussianStochasticGates:Stochastic Gates with Gaussian DistributionMore details about the above mentionedattribution algorithmsand their pros and cons can be found on ourweb-site.LicenseCaptum is BSD licensed, as found in theLICENSEfile.