SMART/WILDS_Experiments/wilds/examples/algorithms/fixmatch.py

import torch
import torch.nn.functional as F

from models.initializer import initialize_model
from algorithms.single_model_algorithm import SingleModelAlgorithm
from configs.supported import process_pseudolabels_functions
from utils import detach_and_clone


class FixMatch(SingleModelAlgorithm):
    """
    FixMatch.
    This algorithm was originally proposed as a semi-supervised learning algorithm.

    Loss is of the form
        \ell_s + \lambda * \ell_u
    where
        \ell_s = cross-entropy with true labels using weakly augmented labeled examples
        \ell_u = cross-entropy with pseudolabel generated using weak augmentation and prediction
            using strong augmentation

    Original paper:
        @article{sohn2020fixmatch,
            title={Fixmatch: Simplifying semi-supervised learning with consistency and confidence},
            author={Sohn, Kihyuk and Berthelot, David and Li, Chun-Liang and Zhang, Zizhao and Carlini, Nicholas and Cubuk, Ekin D and Kurakin, Alex and Zhang, Han and Raffel, Colin},
            journal={arXiv preprint arXiv:2001.07685},
            year={2020}
            }
    """
    def __init__(self, config, d_out, grouper, loss, metric, n_train_steps):
        featurizer, classifier = initialize_model(
            config, d_out=d_out, is_featurizer=True
        )
        model = torch.nn.Sequential(featurizer, classifier)

        # initialize module
        super().__init__(
            config=config,
            model=model,
            grouper=grouper,
            loss=loss,
            metric=metric,
            n_train_steps=n_train_steps,
        )
        # algorithm hyperparameters
        self.fixmatch_lambda = config.self_training_lambda
        self.confidence_threshold = config.self_training_threshold
        self.process_pseudolabels_function = process_pseudolabels_functions[config.process_pseudolabels_function]

        # Additional logging
        self.logged_fields.append("pseudolabels_kept_frac")
        self.logged_fields.append("classification_loss")
        self.logged_fields.append("consistency_loss")

    def process_batch(self, batch, unlabeled_batch=None):
        """
        Overrides single_model_algorithm.process_batch().
        Args:
            - batch (x, y, m): a batch of data yielded by data loaders
            - unlabeled_batch: examples ((x_weak, x_strong), m) where x_weak is weakly augmented but x_strong is strongly augmented
        Output:
            - results (dictionary): information about the batch
                - y_true (Tensor): ground truth labels for batch
                - g (Tensor): groups for batch
                - metadata (Tensor): metadata for batch
                - y_pred (Tensor): model output for batch
                - unlabeled_g (Tensor): groups for unlabeled batch
                - unlabeled_metadata (Tensor): metadata for unlabeled batch
                - unlabeled_weak_y_pseudo (Tensor): pseudolabels on x_weak of the unlabeled batch, already thresholded 
                - unlabeled_strong_y_pred (Tensor): model output on x_strong of the unlabeled batch, already thresholded 
        """
        # Labeled examples
        x, y_true, metadata = batch
        x = x.to(self.device)
        y_true = y_true.to(self.device)
        g = self.grouper.metadata_to_group(metadata).to(self.device)
        # package the results
        results = {
            'g': g,
            'y_true': y_true,
            'metadata': metadata
        }
        pseudolabels_kept_frac = 0

        # Unlabeled examples
        if unlabeled_batch is not None:
            (x_weak, x_strong), metadata = unlabeled_batch
            x_weak = x_weak.to(self.device)
            x_strong = x_strong.to(self.device)

            g = self.grouper.metadata_to_group(metadata).to(self.device)
            results['unlabeled_metadata'] = metadata
            results['unlabeled_g'] = g

            with torch.no_grad():
                outputs = self.model(x_weak)
                _, pseudolabels, pseudolabels_kept_frac, mask = self.process_pseudolabels_function(
                    outputs,
                    self.confidence_threshold,
                )
                results['unlabeled_weak_y_pseudo'] = detach_and_clone(pseudolabels)

        self.save_metric_for_logging(
            results, "pseudolabels_kept_frac", pseudolabels_kept_frac
        )

        # Concat and call forward
        n_lab = x.shape[0]
        if unlabeled_batch is not None:
            x_concat = torch.cat((x, x_strong), dim=0)
        else:
            x_concat = x

        outputs = self.model(x_concat)
        results['y_pred'] = outputs[:n_lab]
        if unlabeled_batch is not None:
            results['unlabeled_strong_y_pred'] = outputs[n_lab:] if mask is None else outputs[n_lab:][mask]
        return results

    def objective(self, results):
        # Labeled loss
        classification_loss = self.loss.compute(results['y_pred'], results['y_true'], return_dict=False)

        # Pseudolabeled loss
        if 'unlabeled_weak_y_pseudo' in results:
            loss_output = self.loss.compute(
                results['unlabeled_strong_y_pred'],
                results['unlabeled_weak_y_pseudo'],
                return_dict=False,
            )
            consistency_loss = loss_output * results['pseudolabels_kept_frac']
        else:
            consistency_loss = 0

        # Add to results for additional logging
        self.save_metric_for_logging(
            results, "classification_loss", classification_loss
        )
        self.save_metric_for_logging(
            results, "consistency_loss", consistency_loss
        )

        return classification_loss + self.fixmatch_lambda * consistency_loss