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meta.py
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meta.py
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import torch
from torch import nn
from torch import optim
from torch.nn import functional as F
from torch.utils.data import TensorDataset, DataLoader
from torch import optim
import numpy as np
from learner import Learner
from copy import deepcopy
class Meta(nn.Module):
"""
Meta Learner
"""
def __init__(self, args, config):
"""
:param args:
"""
super(Meta, self).__init__()
self.update_lr = args.update_lr
self.meta_lr = args.meta_lr
self.n_way = args.n_way
self.k_spt = args.k_spt
self.k_qry = args.k_qry
self.task_num = args.task_num
self.update_step = args.update_step
self.update_step_test = args.update_step_test
self.net = Learner(config, args.imgc, args.imgsz)
self.meta_optim = optim.Adam(self.net.parameters(), lr=self.meta_lr)
def clip_grad_by_norm_(self, grad, max_norm):
"""
in-place gradient clipping.
:param grad: list of gradients
:param max_norm: maximum norm allowable
:return:
"""
total_norm = 0
counter = 0
for g in grad:
param_norm = g.data.norm(2)
total_norm += param_norm.item() ** 2
counter += 1
total_norm = total_norm ** (1. / 2)
clip_coef = max_norm / (total_norm + 1e-6)
if clip_coef < 1:
for g in grad:
g.data.mul_(clip_coef)
return total_norm/counter
def forward(self, x_spt, y_spt, x_qry, y_qry):
"""
:param x_spt: [b, setsz, c_, h, w]
:param y_spt: [b, setsz]
:param x_qry: [b, querysz, c_, h, w]
:param y_qry: [b, querysz]
:return:
"""
task_num, setsz, c_, h, w = x_spt.size()
querysz = x_qry.size(1)
losses_q = [0 for _ in range(self.update_step + 1)] # losses_q[i], i is tasks idx
corrects = [0 for _ in range(self.update_step + 1)]
for i in range(task_num):
# 1. run the i-th task and compute loss for k=0
logits = self.net(x_spt[i], vars=None, bn_training=True)
loss = F.cross_entropy(logits, y_spt[i])
grad = torch.autograd.grad(loss, self.net.parameters())
fast_weights = list(map(lambda p: p[1] - self.update_lr * p[0], zip(grad, self.net.parameters())))
# this is the loss and accuracy before first update
with torch.no_grad():
# [setsz, nway]
logits_q = self.net(x_qry[i], self.net.parameters(), bn_training=True)
loss_q = F.cross_entropy(logits_q, y_qry[i])
losses_q[0] += loss_q
pred_q = F.softmax(logits_q, dim=1).argmax(dim=1)
correct = torch.eq(pred_q, y_qry[i]).sum().item()
corrects[0] = corrects[0] + correct
# this is the loss and accuracy after the first update
with torch.no_grad():
# [setsz, nway]
logits_q = self.net(x_qry[i], fast_weights, bn_training=True)
loss_q = F.cross_entropy(logits_q, y_qry[i])
losses_q[1] += loss_q
# [setsz]
pred_q = F.softmax(logits_q, dim=1).argmax(dim=1)
correct = torch.eq(pred_q, y_qry[i]).sum().item()
corrects[1] = corrects[1] + correct
for k in range(1, self.update_step):
# 1. run the i-th task and compute loss for k=1~K-1
logits = self.net(x_spt[i], fast_weights, bn_training=True)
loss = F.cross_entropy(logits, y_spt[i])
# 2. compute grad on theta_pi
grad = torch.autograd.grad(loss, fast_weights)
# 3. theta_pi = theta_pi - train_lr * grad
fast_weights = list(map(lambda p: p[1] - self.update_lr * p[0], zip(grad, fast_weights)))
logits_q = self.net(x_qry[i], fast_weights, bn_training=True)
# loss_q will be overwritten and just keep the loss_q on last update step.
loss_q = F.cross_entropy(logits_q, y_qry[i])
losses_q[k + 1] += loss_q
with torch.no_grad():
pred_q = F.softmax(logits_q, dim=1).argmax(dim=1)
correct = torch.eq(pred_q, y_qry[i]).sum().item() # convert to numpy
corrects[k + 1] = corrects[k + 1] + correct
# 4. record last step's loss for task i
losses_q.append(loss_q)
# end of all tasks
# sum over all losses on query set across all tasks
loss_q = losses_q[-1] / task_num
# optimize theta parameters
self.meta_optim.zero_grad()
loss_q.backward()
# print('meta update')
# for p in self.net.parameters()[:5]:
# print(torch.norm(p).item())
self.meta_optim.step()
accs = np.array(corrects) / (querysz * task_num)
return accs
def finetunning(self, x_spt, y_spt, x_qry, y_qry):
"""
:param x_spt: [setsz, c_, h, w]
:param y_spt: [setsz]
:param x_qry: [querysz, c_, h, w]
:param y_qry: [querysz]
:return:
"""
assert len(x_spt.shape) == 4
querysz = x_qry.size(0)
corrects = [0 for _ in range(self.update_step_test + 1)]
# in order to not ruin the state of running_mean/variance and bn_weight/bias
# we finetunning on the copied model instead of self.net
net = deepcopy(self.net)
# 1. run the i-th task and compute loss for k=0
logits = net(x_spt)
loss = F.cross_entropy(logits, y_spt)
grad = torch.autograd.grad(loss, net.parameters())
fast_weights = list(map(lambda p: p[1] - self.update_lr * p[0], zip(grad, net.parameters())))
# this is the loss and accuracy before first update
with torch.no_grad():
# [setsz, nway]
logits_q = net(x_qry, net.parameters(), bn_training=True)
# [setsz]
pred_q = F.softmax(logits_q, dim=1).argmax(dim=1)
# scalar
correct = torch.eq(pred_q, y_qry).sum().item()
corrects[0] = corrects[0] + correct
# this is the loss and accuracy after the first update
with torch.no_grad():
# [setsz, nway]
logits_q = net(x_qry, fast_weights, bn_training=True)
# [setsz]
pred_q = F.softmax(logits_q, dim=1).argmax(dim=1)
# scalar
correct = torch.eq(pred_q, y_qry).sum().item()
corrects[1] = corrects[1] + correct
for k in range(1, self.update_step_test):
# 1. run the i-th task and compute loss for k=1~K-1
logits = net(x_spt, fast_weights, bn_training=True)
loss = F.cross_entropy(logits, y_spt)
# 2. compute grad on theta_pi
grad = torch.autograd.grad(loss, fast_weights)
# 3. theta_pi = theta_pi - train_lr * grad
fast_weights = list(map(lambda p: p[1] - self.update_lr * p[0], zip(grad, fast_weights)))
logits_q = net(x_qry, fast_weights, bn_training=True)
# loss_q will be overwritten and just keep the loss_q on last update step.
loss_q = F.cross_entropy(logits_q, y_qry)
with torch.no_grad():
pred_q = F.softmax(logits_q, dim=1).argmax(dim=1)
correct = torch.eq(pred_q, y_qry).sum().item() # convert to numpy
corrects[k + 1] = corrects[k + 1] + correct
del net
accs = np.array(corrects) / querysz
return accs
def main():
pass
if __name__ == '__main__':
main()