# Copyright (C) 2017-2022 Cleanlab Inc.
# This file is part of cleanlab.
#
# cleanlab is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published
# by the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# cleanlab is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with cleanlab. If not, see <https://www.gnu.org/licenses/>.
"""
Implements the co-teaching algorithm for training neural networks on noisily-labeled data (Han et al., 2018).
This module requires PyTorch (https://pytorch.org/get-started/locally/).
Example using this algorithm with cleanlab to achieve state of the art on CIFAR-10
for learning with noisy labels is provided within: https://github.com/cleanlab/examples/
``cifar_cnn.py`` provides an example model that can be trained via this algorithm.
"""
# Significant code was adapted from the following GitHub:
# https://github.com/bhanML/Co-teaching/blob/master/loss.py
# See (Han et al., 2018).
import torch
import torch.nn.functional as F
from torch.autograd import Variable
import numpy as np
MINIMUM_BATCH_SIZE = 16
# Loss function for Co-Teaching
[docs]def loss_coteaching(
y_1,
y_2,
t,
forget_rate,
class_weights=None,
):
"""Co-Teaching Loss function.
Parameters
----------
y_1 : Tensor array
Output logits from model 1
y_2 : Tensor array
Output logits from model 2
t : np.ndarray
List of Noisy Labels (t means targets)
forget_rate : float
Decimal between 0 and 1 for how quickly the models forget what they learn.
Just use rate_schedule[epoch] for this value
class_weights : Tensor array, shape (Number of classes x 1), Default: None
A np.torch.tensor list of length number of classes with weights
"""
loss_1 = F.cross_entropy(y_1, t, reduce=False, weight=class_weights)
ind_1_sorted = np.argsort(loss_1.data.cpu())
loss_1_sorted = loss_1[ind_1_sorted]
loss_2 = F.cross_entropy(y_2, t, reduce=False, weight=class_weights)
ind_2_sorted = np.argsort(loss_2.data.cpu())
remember_rate = 1 - forget_rate
num_remember = int(remember_rate * len(loss_1_sorted))
ind_1_update = ind_1_sorted[:num_remember]
ind_2_update = ind_2_sorted[:num_remember]
# Share updates between the two models.
# TODO: these class weights should take into account the ind_mask filters.
loss_1_update = F.cross_entropy(y_1[ind_2_update], t[ind_2_update], weight=class_weights)
loss_2_update = F.cross_entropy(y_2[ind_1_update], t[ind_1_update], weight=class_weights)
return (
torch.sum(loss_1_update) / num_remember,
torch.sum(loss_2_update) / num_remember,
)
[docs]def initialize_lr_scheduler(lr=0.001, epochs=250, epoch_decay_start=80):
"""Scheduler to adjust learning rate and betas for Adam Optimizer"""
mom1 = 0.9
mom2 = 0.9 # Original author had this set to 0.1
alpha_plan = [lr] * epochs
beta1_plan = [mom1] * epochs
for i in range(epoch_decay_start, epochs):
alpha_plan[i] = float(epochs - i) / (epochs - epoch_decay_start) * lr
beta1_plan[i] = mom2
return alpha_plan, beta1_plan
[docs]def adjust_learning_rate(optimizer, epoch, alpha_plan, beta1_plan):
"""Scheduler to adjust learning rate and betas for Adam Optimizer"""
for param_group in optimizer.param_groups:
param_group["lr"] = alpha_plan[epoch]
param_group["betas"] = (beta1_plan[epoch], 0.999) # Only change beta1
[docs]def forget_rate_scheduler(epochs, forget_rate, num_gradual, exponent):
"""Tells Co-Teaching what fraction of examples to forget at each epoch."""
# define how many things to forget at each rate schedule
forget_rate_schedule = np.ones(epochs) * forget_rate
forget_rate_schedule[:num_gradual] = np.linspace(0, forget_rate**exponent, num_gradual)
return forget_rate_schedule
# Train the Model
[docs]def train(
train_loader,
epoch,
model1,
optimizer1,
model2,
optimizer2,
args,
forget_rate_schedule,
class_weights,
accuracy,
):
"""PyTorch training function.
Parameters
----------
train_loader : torch.utils.data.DataLoader
epoch : int
model1 : PyTorch class inheriting nn.Module
Must define __init__ and forward(self, x,)
optimizer1 : PyTorch torch.optim.Adam
model2 : PyTorch class inheriting nn.Module
Must define __init__ and forward(self, x,)
optimizer2 : PyTorch torch.optim.Adam
args : parser.parse_args() object
Must contain num_iter_per_epoch, print_freq, and epochs
forget_rate_schedule : np.ndarray of length number of epochs
Tells Co-Teaching loss what fraction of examples to forget about.
class_weights : Tensor array, shape (Number of classes x 1), Default: None
A np.torch.tensor list of length number of classes with weights
accuracy : function
A function of the form accuracy(output, target, topk=(1,)) for
computing top1 and top5 accuracy given output and true targets."""
train_total = 0
train_correct = 0
train_total2 = 0
train_correct2 = 0
# Prepare models for training
model1.train()
model2.train()
for i, (images, labels) in enumerate(train_loader):
if i == len(train_loader) - 1 and len(labels) < MINIMUM_BATCH_SIZE:
# Edge case -- the last leftover batch is small (potentially size 1)
# This will happen if, for example, you train on 35101 examples with
# batch size of 450. The last batch will be size 1.
# If you update the weights based on the gradient from one example
# if that example is noisy, you will add tons of noise to your net
# and accuracy will actually go down with each epoch.
# To avoid this, do not train on the last batch if it's small.
continue
images = Variable(images).cuda()
labels = Variable(labels).cuda()
# Forward + Backward + Optimize
logits1 = model1(images)
prec1, _ = accuracy(logits1, labels, topk=(1, 5))
train_total += 1
train_correct += prec1
logits2 = model2(images)
prec2, _ = accuracy(logits2, labels, topk=(1, 5))
train_total2 += 1
train_correct2 += prec2
loss_1, loss_2 = loss_coteaching(
logits1,
logits2,
labels,
forget_rate=forget_rate_schedule[epoch],
class_weights=class_weights,
)
optimizer1.zero_grad()
loss_1.backward()
optimizer1.step()
optimizer2.zero_grad()
loss_2.backward()
optimizer2.step()
if (i + 1) % args.print_freq == 0:
print(
"Epoch [%d/%d], Iter [%d/%d] Training Accuracy1: %.4F, "
"Training Accuracy2: %.4f, Loss1: %.4f, Loss2: %.4f "
% (
epoch + 1,
args.epochs,
i + 1,
len(train_loader.dataset) // args.batch_size,
prec1,
prec2,
loss_1.data.item(),
loss_2.data.item(),
)
)
train_acc1 = float(train_correct) / float(train_total)
train_acc2 = float(train_correct2) / float(train_total2)
return train_acc1, train_acc2
# Evaluate the Model
[docs]def evaluate(test_loader, model1, model2):
print("Evaluating Co-Teaching Model")
model1.eval() # Change model to 'eval' mode.
correct1 = 0
total1 = 0
for images, labels in test_loader:
images = Variable(images).cuda()
logits1 = model1(images)
outputs1 = F.softmax(logits1, dim=1)
_, pred1 = torch.max(outputs1.data, 1)
total1 += labels.size(0)
correct1 += (pred1.cpu() == labels).sum()
model2.eval() # Change model to 'eval' mode
correct2 = 0
total2 = 0
for images, labels in test_loader:
images = Variable(images).cuda()
logits2 = model2(images)
outputs2 = F.softmax(logits2, dim=1)
_, pred2 = torch.max(outputs2.data, 1)
total2 += labels.size(0)
correct2 += (pred2.cpu() == labels).sum()
acc1 = 100 * float(correct1) / float(total1)
acc2 = 100 * float(correct2) / float(total2)
return acc1, acc2