本文将介绍一下六种动态学习率的调整

optim.StepLR,
optim.MultiStepLR,
optim.LambdaLR,
optim.ExponentialLR,
optim.CosineAnnealingLR,
optim.ReduceLROnPlateau

导入工具包

from torch.optim.lr_scheduler import StepLR, MultiStepLR, LambdaLR, ExponentialLR, CosineAnnealingLR, ReduceLROnPlateau
import torch
import torch.nn as nn

LambdaLR,

• new_lr = k * initial_lr
• k是由epoch为自变量算出来的值

initial_lr = 0.1
optimzer_1 = torch.optim.Adam(Net.parameters(),lr = initial_lr)
scheduler_1 = LambdaLR(optimzer_1, lr_lambda=lambda epoch: 1/(epoch + 1))   #y = 1 /(epoch + 1)
print("初始化的学习率：",optimzer_1.defaults['lr'])

for epoch in range(1,11):
    optimzer_1.zero_grad()
    optimzer_1.step()
    print("第%d个epoch的学习率：%f" % (epoch, optimzer_1.param_groups[0]['lr']))
    scheduler_1.step()

StepLR,

• 以epoch等间隔的更新学习率，每次更新-----学习率*gmma—

initial_lr = 0.1
optimzer_1 = torch.optim.Adam(Net.parameters(),lr = initial_lr)
scheduler_1 = StepLR(optimzer_1, step_size=2, gamma=0.1)
print("初始化的学习率：",optimzer_1.defaults['lr'])

for epoch in range(1,11):
    optimzer_1.zero_grad()
    optimzer_1.step()
    print("第%d个epoch的学习率：%f" % (epoch, optimzer_1.param_groups[0]['lr']))
    scheduler_1.step()

MultiStepLR,

• 在指定的epoch上更新学习率

initial_lr = 0.1
optimzer_1 = torch.optim.Adam(Net.parameters(),lr = initial_lr)
scheduler_1 = MultiStepLR(optimzer_1, milestones=[2,6,8], gamma=0.5)
print("初始化的学习率：",optimzer_1.defaults['lr'])

for epoch in range(1,11):
    optimzer_1.zero_grad()
    optimzer_1.step()
    print("第%d个epoch的学习率：%f" % (epoch, optimzer_1.param_groups[0]['lr']))
    scheduler_1.step()

ExponentialLR,

• 指数型的一种学习更新方式—initial * gmma^epoch

initial_lr = 0.1
optimzer_1 = torch.optim.Adam(Net.parameters(),lr = initial_lr)
scheduler_1 = ExponentialLR(optimzer_1, gamma=0.1)
print("初始化的学习率：",optimzer_1.defaults['lr'])

for epoch in range(1,11):
    optimzer_1.zero_grad()
    optimzer_1.step()
    print("第%d个epoch的学习率：%f" % (epoch, optimzer_1.param_groups[0]['lr']))
    scheduler_1.step()

CosineAnnealingLR,

• 一种余弦的学习率调整方式, 变化为一个周期
• new_lr = eta_min + (initial - eta_min) * (1 + cos(epoch * π/T_max))

import matplotlib.pyplot as plt

initial_lr = 0.1
optimzer_1 = torch.optim.Adam(Net.parameters(),lr = initial_lr)
scheduler_1 = CosineAnnealingLR(optimzer_1, T_max=10)
print("初始化的学习率：",optimzer_1.defaults['lr'])

lr_list = []
for epoch in range(1,101):
    optimzer_1.zero_grad()
    optimzer_1.step()
    print("第%d个epoch的学习率：%f" % (epoch, optimzer_1.param_groups[0]['lr']))
    lr_list.append(optimzer_1.param_groups[0]['lr'])
    scheduler_1.step()
    
#画出epoch的变化图
plt.plot(list(range(1,101)),lr_list)
plt.xlabel("epoch")
plt.ylabel("lr")
plt.title("learning rate curve !")
plt.show()

ReduceLROnPlateau

• 根据训练过程中的某些检测量调整学习率

initial_lr = 0.1
optimzer_1 = torch.optim.Adam(Net.parameters(),lr = initial_lr)
scheduler_1 = ReduceLROnPlateau(optimzer_1, mode='min',factor=0.1, patience=2)  #容忍两次还没有更新，开始调整学习率
print("初始化的学习率：",optimzer_1.defaults['lr'])

lr_list = []
for epoch in range(1,15):
    train_loss = 2
    optimzer_1.zero_grad()
    optimzer_1.step()
    print("第%d个epoch的学习率：%f" % (epoch, optimzer_1.param_groups[0]['lr']))
    lr_list.append(optimzer_1.param_groups[0]['lr'])
    scheduler_1.step(train_loss)