algorithms.py

# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved

import torch
import torch.nn as nn
import torch.nn.functional as F
import torch.autograd as autograd
from torch.autograd import Variable

import copy
import numpy as np
from collections import defaultdict

from domainbed import networks
from domainbed.lib.misc import random_pairs_of_minibatches, ParamDict
from domainbed.bottlenecks import *


def get_algorithm_class(algorithm_name):
    """Return the algorithm class with the given name."""
    if algorithm_name not in globals():
        raise NotImplementedError("Algorithm not found: {}".format(algorithm_name))
    return globals()[algorithm_name]


class Algorithm(torch.nn.Module):
    """
    A subclass of Algorithm implements a domain generalization algorithm.
    Subclasses should implement the following:
    - update()
    - predict()
    """

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(Algorithm, self).__init__()
        self.hparams = hparams

    def update(self, minibatches, unlabeled=None):
        """
        Perform one update step, given a list of (x, y) tuples for all
        environments.

        Admits an optional list of unlabeled minibatches from the test domains,
        when task is domain_adaptation.
        """
        raise NotImplementedError

    def predict(self, x):
        raise NotImplementedError


ALGORITHMS = [
    'ERM',
    'Fish',
    'IRM',
    'GroupDRO',
    'Mixup',
    'MLDG',
    'CORAL',
    'MMD',
    'DANN',
    'CDANN',
    'MTL',
    'SagNet',
    'ARM',
    'VREx',
    'RSC',
    'SD',
    'ANDMask',
    'SANDMask',  # SAND-mask
    'IGA',
    'SelfReg',
]

# Include CAD
ALGORITHMS += ['CAD', 'CondCAD']

# Include CLIP algorithms
from domainbed.clip_algorithms import *
ALGORITHMS += CLIP_ALGORITHMS


class ERM(Algorithm):
    """
    Empirical Risk Minimization (ERM)
    """

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(ERM, self).__init__(input_shape, num_classes, num_domains,
                                  hparams)
        self.featurizer = networks.Featurizer(input_shape, self.hparams)
        self.classifier = networks.Classifier(
            self.featurizer.n_outputs,
            num_classes,
            self.hparams['nonlinear_classifier'])

        self.network = nn.Sequential(self.featurizer, self.classifier)
        self.optimizer = torch.optim.Adam(
            self.network.parameters(),
            lr=self.hparams["lr"],
            weight_decay=self.hparams['weight_decay']
        )

    def update(self, minibatches, unlabeled=None):
        all_x = torch.cat([x for x, y in minibatches])
        all_y = torch.cat([y for x, y in minibatches])
        loss = F.cross_entropy(self.predict(all_x), all_y)

        self.optimizer.zero_grad()
        loss.backward()
        self.optimizer.step()

        return {'loss': loss.item()}

    def predict(self, x):
        return self.network(x)


class Fish(Algorithm):
    """
    Implementation of Fish, as seen in Gradient Matching for Domain 
    Generalization, Shi et al. 2021.
    """

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(Fish, self).__init__(input_shape, num_classes, num_domains,
                                   hparams)
        self.input_shape = input_shape
        self.num_classes = num_classes

        self.network = networks.WholeFish(input_shape, num_classes, hparams)
        self.optimizer = torch.optim.Adam(
            self.network.parameters(),
            lr=self.hparams["lr"],
            weight_decay=self.hparams['weight_decay']
        )
        self.optimizer_inner_state = None

    def create_clone(self, device):
        self.network_inner = networks.WholeFish(self.input_shape, self.num_classes, self.hparams,
                                                weights=self.network.state_dict()).to(device)
        self.optimizer_inner = torch.optim.Adam(
            self.network_inner.parameters(),
            lr=self.hparams["lr"],
            weight_decay=self.hparams['weight_decay']
        )
        if self.optimizer_inner_state is not None:
            self.optimizer_inner.load_state_dict(self.optimizer_inner_state)

    def fish(self, meta_weights, inner_weights, lr_meta):
        meta_weights = ParamDict(meta_weights)
        inner_weights = ParamDict(inner_weights)
        meta_weights += lr_meta * (inner_weights - meta_weights)
        return meta_weights

    def update(self, minibatches, unlabeled=None):
        self.create_clone(minibatches[0][0].device)

        for x, y in minibatches:
            loss = F.cross_entropy(self.network_inner(x), y)
            self.optimizer_inner.zero_grad()
            loss.backward()
            self.optimizer_inner.step()

        self.optimizer_inner_state = self.optimizer_inner.state_dict()
        meta_weights = self.fish(
            meta_weights=self.network.state_dict(),
            inner_weights=self.network_inner.state_dict(),
            lr_meta=self.hparams["meta_lr"]
        )
        self.network.reset_weights(meta_weights)

        return {'loss': loss.item()}

    def predict(self, x):
        return self.network(x)


class ARM(ERM):
    """ Adaptive Risk Minimization (ARM) """

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        original_input_shape = input_shape
        input_shape = (1 + original_input_shape[0],) + original_input_shape[1:]
        super(ARM, self).__init__(input_shape, num_classes, num_domains,
                                  hparams)
        self.context_net = networks.ContextNet(original_input_shape)
        self.support_size = hparams['batch_size']

    def predict(self, x):
        batch_size, c, h, w = x.shape
        if batch_size % self.support_size == 0:
            meta_batch_size = batch_size // self.support_size
            support_size = self.support_size
        else:
            meta_batch_size, support_size = 1, batch_size
        context = self.context_net(x)
        context = context.reshape((meta_batch_size, support_size, 1, h, w))
        context = context.mean(dim=1)
        context = torch.repeat_interleave(context, repeats=support_size, dim=0)
        x = torch.cat([x, context], dim=1)
        return self.network(x)


class AbstractDANN(Algorithm):
    """Domain-Adversarial Neural Networks (abstract class)"""

    def __init__(self, input_shape, num_classes, num_domains,
                 hparams, conditional, class_balance):

        super(AbstractDANN, self).__init__(input_shape, num_classes, num_domains,
                                           hparams)

        self.register_buffer('update_count', torch.tensor([0]))
        self.conditional = conditional
        self.class_balance = class_balance

        # Algorithms
        self.featurizer = networks.Featurizer(input_shape, self.hparams)
        self.classifier = networks.Classifier(
            self.featurizer.n_outputs,
            num_classes,
            self.hparams['nonlinear_classifier'])
        self.discriminator = networks.MLP(self.featurizer.n_outputs,
                                          num_domains, self.hparams)
        self.class_embeddings = nn.Embedding(num_classes,
                                             self.featurizer.n_outputs)

        # Optimizers
        self.disc_opt = torch.optim.Adam(
            (list(self.discriminator.parameters()) +
             list(self.class_embeddings.parameters())),
            lr=self.hparams["lr_d"],
            weight_decay=self.hparams['weight_decay_d'],
            betas=(self.hparams['beta1'], 0.9))

        self.gen_opt = torch.optim.Adam(
            (list(self.featurizer.parameters()) +
             list(self.classifier.parameters())),
            lr=self.hparams["lr_g"],
            weight_decay=self.hparams['weight_decay_g'],
            betas=(self.hparams['beta1'], 0.9))

    def update(self, minibatches, unlabeled=None):
        device = "cuda" if minibatches[0][0].is_cuda else "cpu"
        self.update_count += 1
        all_x = torch.cat([x for x, y in minibatches])
        all_y = torch.cat([y for x, y in minibatches])
        all_z = self.featurizer(all_x)
        if self.conditional:
            disc_input = all_z + self.class_embeddings(all_y)
        else:
            disc_input = all_z
        disc_out = self.discriminator(disc_input)
        disc_labels = torch.cat([
            torch.full((x.shape[0],), i, dtype=torch.int64, device=device)
            for i, (x, y) in enumerate(minibatches)
        ])

        if self.class_balance:
            y_counts = F.one_hot(all_y).sum(dim=0)
            weights = 1. / (y_counts[all_y] * y_counts.shape[0]).float()
            disc_loss = F.cross_entropy(disc_out, disc_labels, reduction='none')
            disc_loss = (weights * disc_loss).sum()
        else:
            disc_loss = F.cross_entropy(disc_out, disc_labels)

        disc_softmax = F.softmax(disc_out, dim=1)
        input_grad = autograd.grad(disc_softmax[:, disc_labels].sum(),
                                   [disc_input], create_graph=True)[0]
        grad_penalty = (input_grad ** 2).sum(dim=1).mean(dim=0)
        disc_loss += self.hparams['grad_penalty'] * grad_penalty

        d_steps_per_g = self.hparams['d_steps_per_g_step']
        if (self.update_count.item() % (1 + d_steps_per_g) < d_steps_per_g):

            self.disc_opt.zero_grad()
            disc_loss.backward()
            self.disc_opt.step()
            return {'disc_loss': disc_loss.item()}
        else:
            all_preds = self.classifier(all_z)
            classifier_loss = F.cross_entropy(all_preds, all_y)
            gen_loss = (classifier_loss +
                        (self.hparams['lambda'] * -disc_loss))
            self.disc_opt.zero_grad()
            self.gen_opt.zero_grad()
            gen_loss.backward()
            self.gen_opt.step()
            return {'gen_loss': gen_loss.item()}

    def predict(self, x):
        return self.classifier(self.featurizer(x))


class DANN(AbstractDANN):
    """Unconditional DANN"""

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(DANN, self).__init__(input_shape, num_classes, num_domains,
                                   hparams, conditional=False, class_balance=False)


class CDANN(AbstractDANN):
    """Conditional DANN"""

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(CDANN, self).__init__(input_shape, num_classes, num_domains,
                                    hparams, conditional=True, class_balance=True)


class IRM(ERM):
    """Invariant Risk Minimization"""

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(IRM, self).__init__(input_shape, num_classes, num_domains,
                                  hparams)
        self.register_buffer('update_count', torch.tensor([0]))

    @staticmethod
    def _irm_penalty(logits, y):
        device = "cuda" if logits[0][0].is_cuda else "cpu"
        scale = torch.tensor(1.).to(device).requires_grad_()
        loss_1 = F.cross_entropy(logits[::2] * scale, y[::2])
        loss_2 = F.cross_entropy(logits[1::2] * scale, y[1::2])
        grad_1 = autograd.grad(loss_1, [scale], create_graph=True)[0]
        grad_2 = autograd.grad(loss_2, [scale], create_graph=True)[0]
        result = torch.sum(grad_1 * grad_2)
        return result

    def update(self, minibatches, unlabeled=None):
        device = "cuda" if minibatches[0][0].is_cuda else "cpu"
        penalty_weight = (self.hparams['irm_lambda'] if self.update_count
                                                        >= self.hparams['irm_penalty_anneal_iters'] else
                          1.0)
        nll = 0.
        penalty = 0.

        all_x = torch.cat([x for x, y in minibatches])
        all_logits = self.network(all_x)
        all_logits_idx = 0
        for i, (x, y) in enumerate(minibatches):
            logits = all_logits[all_logits_idx:all_logits_idx + x.shape[0]]
            all_logits_idx += x.shape[0]
            nll += F.cross_entropy(logits, y)
            penalty += self._irm_penalty(logits, y)
        nll /= len(minibatches)
        penalty /= len(minibatches)
        loss = nll + (penalty_weight * penalty)

        if self.update_count == self.hparams['irm_penalty_anneal_iters']:
            # Reset Adam, because it doesn't like the sharp jump in gradient
            # magnitudes that happens at this step.
            self.optimizer = torch.optim.Adam(
                self.network.parameters(),
                lr=self.hparams["lr"],
                weight_decay=self.hparams['weight_decay'])

        self.optimizer.zero_grad()
        loss.backward()
        self.optimizer.step()

        self.update_count += 1
        return {'loss': loss.item(), 'nll': nll.item(),
                'penalty': penalty.item()}


class VREx(ERM):
    """V-REx algorithm from http://arxiv.org/abs/2003.00688"""

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(VREx, self).__init__(input_shape, num_classes, num_domains,
                                   hparams)
        self.register_buffer('update_count', torch.tensor([0]))

    def update(self, minibatches, unlabeled=None):
        if self.update_count >= self.hparams["vrex_penalty_anneal_iters"]:
            penalty_weight = self.hparams["vrex_lambda"]
        else:
            penalty_weight = 1.0

        nll = 0.

        all_x = torch.cat([x for x, y in minibatches])
        all_logits = self.network(all_x)
        all_logits_idx = 0
        losses = torch.zeros(len(minibatches))
        for i, (x, y) in enumerate(minibatches):
            logits = all_logits[all_logits_idx:all_logits_idx + x.shape[0]]
            all_logits_idx += x.shape[0]
            nll = F.cross_entropy(logits, y)
            losses[i] = nll

        mean = losses.mean()
        penalty = ((losses - mean) ** 2).mean()
        loss = mean + penalty_weight * penalty

        if self.update_count == self.hparams['vrex_penalty_anneal_iters']:
            # Reset Adam (like IRM), because it doesn't like the sharp jump in
            # gradient magnitudes that happens at this step.
            self.optimizer = torch.optim.Adam(
                self.network.parameters(),
                lr=self.hparams["lr"],
                weight_decay=self.hparams['weight_decay'])

        self.optimizer.zero_grad()
        loss.backward()
        self.optimizer.step()

        self.update_count += 1
        return {'loss': loss.item(), 'nll': nll.item(),
                'penalty': penalty.item()}


class Mixup(ERM):
    """
    Mixup of minibatches from different domains
    https://arxiv.org/pdf/2001.00677.pdf
    https://arxiv.org/pdf/1912.01805.pdf
    """

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(Mixup, self).__init__(input_shape, num_classes, num_domains,
                                    hparams)

    def update(self, minibatches, unlabeled=None):
        objective = 0

        for (xi, yi), (xj, yj) in random_pairs_of_minibatches(minibatches):
            lam = np.random.beta(self.hparams["mixup_alpha"],
                                 self.hparams["mixup_alpha"])

            x = lam * xi + (1 - lam) * xj
            predictions = self.predict(x)

            objective += lam * F.cross_entropy(predictions, yi)
            objective += (1 - lam) * F.cross_entropy(predictions, yj)

        objective /= len(minibatches)

        self.optimizer.zero_grad()
        objective.backward()
        self.optimizer.step()

        return {'loss': objective.item()}


class GroupDRO(ERM):
    """
    Robust ERM minimizes the error at the worst minibatch
    Algorithm 1 from [https://arxiv.org/pdf/1911.08731.pdf]
    """

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(GroupDRO, self).__init__(input_shape, num_classes, num_domains,
                                       hparams)
        self.register_buffer("q", torch.Tensor())

    def update(self, minibatches, unlabeled=None):
        device = "cuda" if minibatches[0][0].is_cuda else "cpu"

        if not len(self.q):
            self.q = torch.ones(len(minibatches)).to(device)

        losses = torch.zeros(len(minibatches)).to(device)

        for m in range(len(minibatches)):
            x, y = minibatches[m]
            losses[m] = F.cross_entropy(self.predict(x), y)
            self.q[m] *= (self.hparams["groupdro_eta"] * losses[m].data).exp()

        self.q /= self.q.sum()

        loss = torch.dot(losses, self.q)

        self.optimizer.zero_grad()
        loss.backward()
        self.optimizer.step()

        return {'loss': loss.item()}


class MLDG(ERM):
    """
    Model-Agnostic Meta-Learning
    Algorithm 1 / Equation (3) from: https://arxiv.org/pdf/1710.03463.pdf
    Related: https://arxiv.org/pdf/1703.03400.pdf
    Related: https://arxiv.org/pdf/1910.13580.pdf
    """

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(MLDG, self).__init__(input_shape, num_classes, num_domains,
                                   hparams)

    def update(self, minibatches, unlabeled=None):
        """
        Terms being computed:
            * Li = Loss(xi, yi, params)
            * Gi = Grad(Li, params)

            * Lj = Loss(xj, yj, Optimizer(params, grad(Li, params)))
            * Gj = Grad(Lj, params)

            * params = Optimizer(params, Grad(Li + beta * Lj, params))
            *        = Optimizer(params, Gi + beta * Gj)

        That is, when calling .step(), we want grads to be Gi + beta * Gj

        For computational efficiency, we do not compute second derivatives.
        """
        num_mb = len(minibatches)
        objective = 0

        self.optimizer.zero_grad()
        for p in self.network.parameters():
            if p.grad is None:
                p.grad = torch.zeros_like(p)

        for (xi, yi), (xj, yj) in random_pairs_of_minibatches(minibatches):
            # fine tune clone-network on task "i"
            inner_net = copy.deepcopy(self.network)

            inner_opt = torch.optim.Adam(
                inner_net.parameters(),
                lr=self.hparams["lr"],
                weight_decay=self.hparams['weight_decay']
            )

            inner_obj = F.cross_entropy(inner_net(xi), yi)

            inner_opt.zero_grad()
            inner_obj.backward()
            inner_opt.step()

            # The network has now accumulated gradients Gi
            # The clone-network has now parameters P - lr * Gi
            for p_tgt, p_src in zip(self.network.parameters(),
                                    inner_net.parameters()):
                if p_src.grad is not None:
                    p_tgt.grad.data.add_(p_src.grad.data / num_mb)

            # `objective` is populated for reporting purposes
            objective += inner_obj.item()

            # this computes Gj on the clone-network
            loss_inner_j = F.cross_entropy(inner_net(xj), yj)
            grad_inner_j = autograd.grad(loss_inner_j, inner_net.parameters(),
                                         allow_unused=True)

            # `objective` is populated for reporting purposes
            objective += (self.hparams['mldg_beta'] * loss_inner_j).item()

            for p, g_j in zip(self.network.parameters(), grad_inner_j):
                if g_j is not None:
                    p.grad.data.add_(
                        self.hparams['mldg_beta'] * g_j.data / num_mb)

            # The network has now accumulated gradients Gi + beta * Gj
            # Repeat for all train-test splits, do .step()

        objective /= len(minibatches)

        self.optimizer.step()

        return {'loss': objective}

    # This commented "update" method back-propagates through the gradients of
    # the inner update, as suggested in the original MAML paper.  However, this
    # is twice as expensive as the uncommented "update" method, which does not
    # compute second-order derivatives, implementing the First-Order MAML
    # method (FOMAML) described in the original MAML paper.

    # def update(self, minibatches, unlabeled=None):
    #     objective = 0
    #     beta = self.hparams["beta"]
    #     inner_iterations = self.hparams["inner_iterations"]

    #     self.optimizer.zero_grad()

    #     with higher.innerloop_ctx(self.network, self.optimizer,
    #         copy_initial_weights=False) as (inner_network, inner_optimizer):

    #         for (xi, yi), (xj, yj) in random_pairs_of_minibatches(minibatches):
    #             for inner_iteration in range(inner_iterations):
    #                 li = F.cross_entropy(inner_network(xi), yi)
    #                 inner_optimizer.step(li)
    #
    #             objective += F.cross_entropy(self.network(xi), yi)
    #             objective += beta * F.cross_entropy(inner_network(xj), yj)

    #         objective /= len(minibatches)
    #         objective.backward()
    #
    #     self.optimizer.step()
    #
    #     return objective


class AbstractMMD(ERM):
    """
    Perform ERM while matching the pair-wise domain feature distributions
    using MMD (abstract class)
    """

    def __init__(self, input_shape, num_classes, num_domains, hparams, gaussian):
        super(AbstractMMD, self).__init__(input_shape, num_classes, num_domains,
                                          hparams)
        if gaussian:
            self.kernel_type = "gaussian"
        else:
            self.kernel_type = "mean_cov"

    def my_cdist(self, x1, x2):
        x1_norm = x1.pow(2).sum(dim=-1, keepdim=True)
        x2_norm = x2.pow(2).sum(dim=-1, keepdim=True)
        res = torch.addmm(x2_norm.transpose(-2, -1),
                          x1,
                          x2.transpose(-2, -1), alpha=-2).add_(x1_norm)
        return res.clamp_min_(1e-30)

    def gaussian_kernel(self, x, y, gamma=[0.001, 0.01, 0.1, 1, 10, 100,
                                           1000]):
        D = self.my_cdist(x, y)
        K = torch.zeros_like(D)

        for g in gamma:
            K.add_(torch.exp(D.mul(-g)))

        return K

    def mmd(self, x, y):
        if self.kernel_type == "gaussian":
            Kxx = self.gaussian_kernel(x, x).mean()
            Kyy = self.gaussian_kernel(y, y).mean()
            Kxy = self.gaussian_kernel(x, y).mean()
            return Kxx + Kyy - 2 * Kxy
        else:
            mean_x = x.mean(0, keepdim=True)
            mean_y = y.mean(0, keepdim=True)
            cent_x = x - mean_x
            cent_y = y - mean_y
            cova_x = (cent_x.t() @ cent_x) / (len(x) - 1)
            cova_y = (cent_y.t() @ cent_y) / (len(y) - 1)

            mean_diff = (mean_x - mean_y).pow(2).mean()
            cova_diff = (cova_x - cova_y).pow(2).mean()

            return mean_diff + cova_diff

    def update(self, minibatches, unlabeled=None):
        objective = 0
        penalty = 0
        nmb = len(minibatches)

        features = [self.featurizer(xi) for xi, _ in minibatches]
        classifs = [self.classifier(fi) for fi in features]
        targets = [yi for _, yi in minibatches]

        for i in range(nmb):
            objective += F.cross_entropy(classifs[i], targets[i])
            for j in range(i + 1, nmb):
                penalty += self.mmd(features[i], features[j])

        objective /= nmb
        if nmb > 1:
            penalty /= (nmb * (nmb - 1) / 2)

        self.optimizer.zero_grad()
        (objective + (self.hparams['mmd_gamma'] * penalty)).backward()
        self.optimizer.step()

        if torch.is_tensor(penalty):
            penalty = penalty.item()

        return {'loss': objective.item(), 'penalty': penalty}


class MMD(AbstractMMD):
    """
    MMD using Gaussian kernel
    """

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(MMD, self).__init__(input_shape, num_classes,
                                  num_domains, hparams, gaussian=True)


class CORAL(AbstractMMD):
    """
    MMD using mean and covariance difference
    """

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(CORAL, self).__init__(input_shape, num_classes,
                                    num_domains, hparams, gaussian=False)


class MTL(Algorithm):
    """
    A neural network version of
    Domain Generalization by Marginal Transfer Learning
    (https://arxiv.org/abs/1711.07910)
    """

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(MTL, self).__init__(input_shape, num_classes, num_domains,
                                  hparams)
        self.featurizer = networks.Featurizer(input_shape, self.hparams)
        self.classifier = networks.Classifier(
            self.featurizer.n_outputs * 2,
            num_classes,
            self.hparams['nonlinear_classifier'])
        self.optimizer = torch.optim.Adam(
            list(self.featurizer.parameters()) + \
            list(self.classifier.parameters()),
            lr=self.hparams["lr"],
            weight_decay=self.hparams['weight_decay']
        )

        self.register_buffer('embeddings',
                             torch.zeros(num_domains,
                                         self.featurizer.n_outputs))

        self.ema = self.hparams['mtl_ema']

    def update(self, minibatches, unlabeled=None):
        loss = 0
        for env, (x, y) in enumerate(minibatches):
            loss += F.cross_entropy(self.predict(x, env), y)

        self.optimizer.zero_grad()
        loss.backward()
        self.optimizer.step()

        return {'loss': loss.item()}

    def update_embeddings_(self, features, env=None):
        return_embedding = features.mean(0)

        if env is not None:
            return_embedding = self.ema * return_embedding + \
                               (1 - self.ema) * self.embeddings[env]

            self.embeddings[env] = return_embedding.clone().detach()

        return return_embedding.view(1, -1).repeat(len(features), 1)

    def predict(self, x, env=None):
        features = self.featurizer(x)
        embedding = self.update_embeddings_(features, env).normal_()
        return self.classifier(torch.cat((features, embedding), 1))


class SagNet(Algorithm):
    """
    Style Agnostic Network
    Algorithm 1 from: https://arxiv.org/abs/1910.11645
    """

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(SagNet, self).__init__(input_shape, num_classes, num_domains,
                                     hparams)
        # featurizer network
        self.network_f = networks.Featurizer(input_shape, self.hparams)
        # content network
        self.network_c = networks.Classifier(
            self.network_f.n_outputs,
            num_classes,
            self.hparams['nonlinear_classifier'])
        # style network
        self.network_s = networks.Classifier(
            self.network_f.n_outputs,
            num_classes,
            self.hparams['nonlinear_classifier'])

        # # This commented block of code implements something closer to the
        # # original paper, but is specific to ResNet and puts in disadvantage
        # # the other algorithms.
        # resnet_c = networks.Featurizer(input_shape, self.hparams)
        # resnet_s = networks.Featurizer(input_shape, self.hparams)
        # # featurizer network
        # self.network_f = torch.nn.Sequential(
        #         resnet_c.network.conv1,
        #         resnet_c.network.bn1,
        #         resnet_c.network.relu,
        #         resnet_c.network.maxpool,
        #         resnet_c.network.layer1,
        #         resnet_c.network.layer2,
        #         resnet_c.network.layer3)
        # # content network
        # self.network_c = torch.nn.Sequential(
        #         resnet_c.network.layer4,
        #         resnet_c.network.avgpool,
        #         networks.Flatten(),
        #         resnet_c.network.fc)
        # # style network
        # self.network_s = torch.nn.Sequential(
        #         resnet_s.network.layer4,
        #         resnet_s.network.avgpool,
        #         networks.Flatten(),
        #         resnet_s.network.fc)

        def opt(p):
            return torch.optim.Adam(p, lr=hparams["lr"],
                                    weight_decay=hparams["weight_decay"])

        self.optimizer_f = opt(self.network_f.parameters())
        self.optimizer_c = opt(self.network_c.parameters())
        self.optimizer_s = opt(self.network_s.parameters())
        self.weight_adv = hparams["sag_w_adv"]

    def forward_c(self, x):
        # learning content network on randomized style
        return self.network_c(self.randomize(self.network_f(x), "style"))

    def forward_s(self, x):
        # learning style network on randomized content
        return self.network_s(self.randomize(self.network_f(x), "content"))

    def randomize(self, x, what="style", eps=1e-5):
        device = "cuda" if x.is_cuda else "cpu"
        sizes = x.size()
        alpha = torch.rand(sizes[0], 1).to(device)

        if len(sizes) == 4:
            x = x.view(sizes[0], sizes[1], -1)
            alpha = alpha.unsqueeze(-1)

        mean = x.mean(-1, keepdim=True)
        var = x.var(-1, keepdim=True)

        x = (x - mean) / (var + eps).sqrt()

        idx_swap = torch.randperm(sizes[0])
        if what == "style":
            mean = alpha * mean + (1 - alpha) * mean[idx_swap]
            var = alpha * var + (1 - alpha) * var[idx_swap]
        else:
            x = x[idx_swap].detach()

        x = x * (var + eps).sqrt() + mean
        return x.view(*sizes)

    def update(self, minibatches, unlabeled=None):
        all_x = torch.cat([x for x, y in minibatches])
        all_y = torch.cat([y for x, y in minibatches])

        # learn content
        self.optimizer_f.zero_grad()
        self.optimizer_c.zero_grad()
        loss_c = F.cross_entropy(self.forward_c(all_x), all_y)
        loss_c.backward()
        self.optimizer_f.step()
        self.optimizer_c.step()

        # learn style
        self.optimizer_s.zero_grad()
        loss_s = F.cross_entropy(self.forward_s(all_x), all_y)
        loss_s.backward()
        self.optimizer_s.step()

        # learn adversary
        self.optimizer_f.zero_grad()
        loss_adv = -F.log_softmax(self.forward_s(all_x), dim=1).mean(1).mean()
        loss_adv = loss_adv * self.weight_adv
        loss_adv.backward()
        self.optimizer_f.step()

        return {'loss_c': loss_c.item(), 'loss_s': loss_s.item(),
                'loss_adv': loss_adv.item()}

    def predict(self, x):
        return self.network_c(self.network_f(x))


class RSC(ERM):
    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(RSC, self).__init__(input_shape, num_classes, num_domains,
                                  hparams)
        self.drop_f = (1 - hparams['rsc_f_drop_factor']) * 100
        self.drop_b = (1 - hparams['rsc_b_drop_factor']) * 100
        self.num_classes = num_classes

    def update(self, minibatches, unlabeled=None):
        device = "cuda" if minibatches[0][0].is_cuda else "cpu"

        # inputs
        all_x = torch.cat([x for x, y in minibatches])
        # labels
        all_y = torch.cat([y for _, y in minibatches])
        # one-hot labels
        all_o = torch.nn.functional.one_hot(all_y, self.num_classes)
        # features
        all_f = self.featurizer(all_x)
        # predictions
        all_p = self.classifier(all_f)

        # Equation (1): compute gradients with respect to representation
        all_g = autograd.grad((all_p * all_o).sum(), all_f)[0]

        # Equation (2): compute top-gradient-percentile mask
        percentiles = np.percentile(all_g.cpu(), self.drop_f, axis=1)
        percentiles = torch.Tensor(percentiles)
        percentiles = percentiles.unsqueeze(1).repeat(1, all_g.size(1))
        mask_f = all_g.lt(percentiles.to(device)).float()

        # Equation (3): mute top-gradient-percentile activations
        all_f_muted = all_f * mask_f

        # Equation (4): compute muted predictions
        all_p_muted = self.classifier(all_f_muted)

        # Section 3.3: Batch Percentage
        all_s = F.softmax(all_p, dim=1)
        all_s_muted = F.softmax(all_p_muted, dim=1)
        changes = (all_s * all_o).sum(1) - (all_s_muted * all_o).sum(1)
        percentile = np.percentile(changes.detach().cpu(), self.drop_b)
        mask_b = changes.lt(percentile).float().view(-1, 1)
        mask = torch.logical_or(mask_f, mask_b).float()

        # Equations (3) and (4) again, this time mutting over examples
        all_p_muted_again = self.classifier(all_f * mask)

        # Equation (5): update
        loss = F.cross_entropy(all_p_muted_again, all_y)
        self.optimizer.zero_grad()
        loss.backward()
        self.optimizer.step()

        return {'loss': loss.item()}


class SD(ERM):
    """
    Gradient Starvation: A Learning Proclivity in Neural Networks
    Equation 25 from [https://arxiv.org/pdf/2011.09468.pdf]
    """

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(SD, self).__init__(input_shape, num_classes, num_domains,
                                 hparams)
        self.sd_reg = hparams["sd_reg"]

    def update(self, minibatches, unlabeled=None):
        all_x = torch.cat([x for x, y in minibatches])
        all_y = torch.cat([y for x, y in minibatches])
        all_p = self.predict(all_x)

        loss = F.cross_entropy(all_p, all_y)
        penalty = (all_p ** 2).mean()
        objective = loss + self.sd_reg * penalty

        self.optimizer.zero_grad()
        objective.backward()
        self.optimizer.step()

        return {'loss': loss.item(), 'penalty': penalty.item()}


class ANDMask(ERM):
    """
    Learning Explanations that are Hard to Vary [https://arxiv.org/abs/2009.00329]
    AND-Mask implementation from [https://github.com/gibipara92/learning-explanations-hard-to-vary]
    """

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(ANDMask, self).__init__(input_shape, num_classes, num_domains, hparams)

        self.tau = hparams["tau"]

    def update(self, minibatches, unlabeled=None):

        total_loss = 0
        param_gradients = [[] for _ in self.network.parameters()]
        all_x = torch.cat([x for x, y in minibatches])
        all_logits = self.network(all_x)
        all_logits_idx = 0
        for i, (x, y) in enumerate(minibatches):
            logits = all_logits[all_logits_idx:all_logits_idx + x.shape[0]]
            all_logits_idx += x.shape[0]

            env_loss = F.cross_entropy(logits, y)
            total_loss += env_loss

            env_grads = autograd.grad(env_loss, self.network.parameters(), retain_graph=True)
            for grads, env_grad in zip(param_gradients, env_grads):
                grads.append(env_grad)

        mean_loss = total_loss / len(minibatches)

        self.optimizer.zero_grad()
        self.mask_grads(self.tau, param_gradients, self.network.parameters())
        self.optimizer.step()

        return {'loss': mean_loss.item()}

    def mask_grads(self, tau, gradients, params):

        for param, grads in zip(params, gradients):
            grads = torch.stack(grads, dim=0)
            grad_signs = torch.sign(grads)
            mask = torch.mean(grad_signs, dim=0).abs() >= self.tau
            mask = mask.to(torch.float32)
            avg_grad = torch.mean(grads, dim=0)

            mask_t = (mask.sum() / mask.numel())
            param.grad = mask * avg_grad
            param.grad *= (1. / (1e-10 + mask_t))

        return 0


class IGA(ERM):
    """
    Inter-environmental Gradient Alignment
    From https://arxiv.org/abs/2008.01883v2
    """

    def __init__(self, in_features, num_classes, num_domains, hparams):
        super(IGA, self).__init__(in_features, num_classes, num_domains, hparams)

    def update(self, minibatches, unlabeled=False):

        all_x = torch.cat([x for x, y in minibatches])
        all_logits = self.network(all_x)

        total_loss = 0
        all_logits_idx = 0
        grads = []
        for i, (x, y) in enumerate(minibatches):
            logits = all_logits[all_logits_idx:all_logits_idx + x.shape[0]]
            all_logits_idx += x.shape[0]

            env_loss = F.cross_entropy(logits, y)
            total_loss += env_loss

            env_grad = autograd.grad(env_loss, self.network.parameters(),
                                     create_graph=True)

            grads.append(env_grad)

        mean_loss = total_loss / len(minibatches)
        mean_grad = autograd.grad(mean_loss, self.network.parameters(),
                                  create_graph=True)

        # compute trace penalty
        penalty_value = 0
        for grad in grads:
            for g, mean_g in zip(grad, mean_grad):
                penalty_value += (g - mean_g).pow(2).sum()

        objective = mean_loss + self.hparams['penalty'] * penalty_value

        self.optimizer.zero_grad()
        objective.backward()
        self.optimizer.step()

        return {'loss': mean_loss.item(), 'penalty': penalty_value.item()}


class SelfReg(ERM):
    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(SelfReg, self).__init__(input_shape, num_classes, num_domains,
                                      hparams)
        self.num_classes = num_classes
        self.MSEloss = nn.MSELoss()
        input_feat_size = self.featurizer.n_outputs
        hidden_size = input_feat_size if input_feat_size == 2048 else input_feat_size * 2

        self.cdpl = nn.Sequential(
            nn.Linear(input_feat_size, hidden_size),
            nn.BatchNorm1d(hidden_size),
            nn.ReLU(inplace=True),
            nn.Linear(hidden_size, hidden_size),
            nn.BatchNorm1d(hidden_size),
            nn.ReLU(inplace=True),
            nn.Linear(hidden_size, input_feat_size),
            nn.BatchNorm1d(input_feat_size)
        )

    def update(self, minibatches, unlabeled=None):

        all_x = torch.cat([x for x, y in minibatches])
        all_y = torch.cat([y for _, y in minibatches])

        lam = np.random.beta(0.5, 0.5)

        batch_size = all_y.size()[0]

        # cluster and order features into same-class group
        with torch.no_grad():
            sorted_y, indices = torch.sort(all_y)
            sorted_x = torch.zeros_like(all_x)
            for idx, order in enumerate(indices):
                sorted_x[idx] = all_x[order]
            intervals = []
            ex = 0
            for idx, val in enumerate(sorted_y):
                if ex == val:
                    continue
                intervals.append(idx)
                ex = val
            intervals.append(batch_size)

            all_x = sorted_x
            all_y = sorted_y

        feat = self.featurizer(all_x)
        proj = self.cdpl(feat)

        output = self.classifier(feat)

        # shuffle
        output_2 = torch.zeros_like(output)
        feat_2 = torch.zeros_like(proj)
        output_3 = torch.zeros_like(output)
        feat_3 = torch.zeros_like(proj)
        ex = 0
        for end in intervals:
            shuffle_indices = torch.randperm(end - ex) + ex
            shuffle_indices2 = torch.randperm(end - ex) + ex
            for idx in range(end - ex):
                output_2[idx + ex] = output[shuffle_indices[idx]]
                feat_2[idx + ex] = proj[shuffle_indices[idx]]
                output_3[idx + ex] = output[shuffle_indices2[idx]]
                feat_3[idx + ex] = proj[shuffle_indices2[idx]]
            ex = end

        # mixup 
        output_3 = lam * output_2 + (1 - lam) * output_3
        feat_3 = lam * feat_2 + (1 - lam) * feat_3

        # regularization
        L_ind_logit = self.MSEloss(output, output_2)
        L_hdl_logit = self.MSEloss(output, output_3)
        L_ind_feat = 0.3 * self.MSEloss(feat, feat_2)
        L_hdl_feat = 0.3 * self.MSEloss(feat, feat_3)

        cl_loss = F.cross_entropy(output, all_y)
        C_scale = min(cl_loss.item(), 1.)
        loss = cl_loss + C_scale * (lam * (L_ind_logit + L_ind_feat) + (1 - lam) * (L_hdl_logit + L_hdl_feat))

        self.optimizer.zero_grad()
        loss.backward()
        self.optimizer.step()

        return {'loss': loss.item()}


class SANDMask(ERM):
    """
    SAND-mask: An Enhanced Gradient Masking Strategy for the Discovery of Invariances in Domain Generalization
    <https://arxiv.org/abs/2106.02266>
    """

    def __init__(self, input_shape, num_classes, num_domains, hparams):
        super(SANDMask, self).__init__(input_shape, num_classes, num_domains, hparams)

        self.tau = hparams["tau"]
        self.k = hparams["k"]
        betas = (0.9, 0.999)
        self.optimizer = torch.optim.Adam(
            self.network.parameters(),
            lr=self.hparams["lr"],
            weight_decay=self.hparams['weight_decay'],
            betas=betas
        )

        self.register_buffer('update_count', torch.tensor([0]))

    def update(self, minibatches, unlabeled=None):

        total_loss = 0
        param_gradients = [[] for _ in self.network.parameters()]
        all_x = torch.cat([x for x, y in minibatches])
        all_logits = self.network(all_x)
        all_logits_idx = 0
        for i, (x, y) in enumerate(minibatches):
            logits = all_logits[all_logits_idx:all_logits_idx + x.shape[0]]
            all_logits_idx += x.shape[0]

            env_loss = F.cross_entropy(logits, y)
            total_loss += env_loss
            env_grads = autograd.grad(env_loss, self.network.parameters(), retain_graph=True)
            for grads, env_grad in zip(param_gradients, env_grads):
                grads.append(env_grad)

        mean_loss = total_loss / len(minibatches)

        self.optimizer.zero_grad()
        # gradient masking applied here
        self.mask_grads(param_gradients, self.network.parameters())
        self.optimizer.step()
        self.update_count += 1

        return {'loss': mean_loss.item()}

    def mask_grads(self, gradients, params):
        '''
        Here a mask with continuous values in the range [0,1] is formed to control the amount of update for each
        parameter based on the agreement of gradients coming from different environments.
        '''
        device = gradients[0][0].device
        for param, grads in zip(params, gradients):
            grads = torch.stack(grads, dim=0)
            avg_grad = torch.mean(grads, dim=0)
            grad_signs = torch.sign(grads)
            gamma = torch.tensor(1.0).to(device)
            grads_var = grads.var(dim=0)
            grads_var[torch.isnan(grads_var)] = 1e-17
            lam = (gamma * grads_var).pow(-1)
            mask = torch.tanh(self.k * lam * (torch.abs(grad_signs.mean(dim=0)) - self.tau))
            mask = torch.max(mask, torch.zeros_like(mask))
            mask[torch.isnan(mask)] = 1e-17
            mask_t = (mask.sum() / mask.numel())
            param.grad = mask * avg_grad
            param.grad *= (1. / (1e-10 + mask_t))


class AbstractBN(Algorithm):
    """Bottleneck (abstract class)"""

    def __init__(self, input_shape, num_classes, num_domains,
                 hparams, bottleneck_class):
        super(AbstractBN, self).__init__(input_shape, num_classes, num_domains, hparams)

        # Algorithms
        self.featurizer = networks.Featurizer(input_shape, self.hparams)
        self.classifier = networks.Classifier(
            self.featurizer.n_outputs,
            num_classes,
            self.hparams['nonlinear_classifier'])
        params = list(self.featurizer.parameters()) + list(self.classifier.parameters())

        self.bottleneck = bottleneck_class(self.featurizer.n_outputs, num_classes, num_domains, hparams)

        if self.bottleneck.trainable:
            params += list(self.bottleneck.parameters())

        # Optimizers
        self.optimizer = torch.optim.Adam(
            params,
            lr=self.hparams["lr"],
            weight_decay=self.hparams['weight_decay']
        )

    def update(self, minibatches, unlabeled=None):
        device = "cuda" if minibatches[0][0].is_cuda else "cpu"
        all_x = torch.cat([x for x, y in minibatches])
        all_y = torch.cat([y for x, y in minibatches])
        all_z = self.featurizer(all_x)
        all_d = torch.cat([
            torch.full((x.shape[0],), i, dtype=torch.int64, device=device)
            for i, (x, y) in enumerate(minibatches)
        ])

        bn_loss, all_z_hat = self.bottleneck.loss(all_z, all_y, all_d)
        clf_out = self.classifier(all_z_hat)
        clf_loss = F.cross_entropy(clf_out, all_y)
        total_loss = clf_loss + self.hparams['lmbda'] * bn_loss

        self.optimizer.zero_grad()
        total_loss.backward()
        self.optimizer.step()

        return {"clf_loss": clf_loss.item(), "bn_loss": bn_loss.item(), "total_loss": total_loss.item()}

    def predict(self, x):
        return self.classifier(self.bottleneck(self.featurizer(x)))


class CAD(AbstractBN):
    def __init__(self, feature_dim, num_classes, num_domains, hparams):
        super(CAD, self).__init__(feature_dim, num_classes, num_domains, hparams, CADBottleneck)


class CondCAD(AbstractBN):
    def __init__(self, feature_dim, num_classes, num_domains, hparams):
        super(CondCAD, self).__init__(feature_dim, num_classes, num_domains, hparams, CondCADBottleneck)