PyTorch学习笔记(17)损失函数(二)
损失函数
nn.L2Loss
功能 计算inputs 与 target 之差的绝对值
nn.MSELoss
功能 计算inputs 与 target 之差的平方
主要参数
reduction 计算模式,可为none/sum/mean
none -逐个元素计算
sum -所有元素求和,返回标量
mean -加权平均,返回标量
SmoothL1Loss
功能 平滑的L1Loss
主要参数
reduction 计算模式,可为none/sum/mean
none -逐个元素计算
sum -所有元素求和,返回标量
mean -加权平均,返回标量
PoissonNLLLoss
功能 泊松分布的负对数似然损失函数
主要参数
log_input 输入是否为对数形式,决定计算公式
full 计算所有loss 默认为False
eps 修正项,避免log(input) 为nan
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log_input $̲=$ False
nn.KLDivLoss
功能:计算KLD(divergence),KL散度,相对熵 注意事项:需提前将输入计算log-probabilities,如通过nn.logsoftmax()
主要参数
reduction : none/sum/mean/batchmean
batchmean- batchsize维度求平均值
none -逐个元素计算
sum -所有元素求和,返回标量
mean -加权平均,返回标量
nn.MarginRankingLoss
功能 计算两个向量之间的相似度,用于排序任务
特殊说明 该方法计算两组数据之间的差异,返回一个n*n的loss矩阵
主要参数
margin 边界值,x1与x2之间的差异值
reduction 计算模式,可为none/sum/mean
y = 1时,希望x1比x2大,当x1>x2时,不产生loss
y = -1时,希望x2比x1大,当x2>x1时,不产生loss
nn.MultiLabelMarginLoss
功能 多标签边界损失函数
主要参数
reduction 计算模式,可为none/sum/mean
nn.SoftMarginLoss
功能 计算二分类的logistic损失
主要参数
reduction 计算模式,可为none/sum/mean
#·
reduction 计算模式,可为none/sum/mean
nn.MultiMarginLoss
功能 计算多分类的折页损失
主要参数
p 可选1或2
weight 各类别的loss设置权值
margin 边界值
reduction 计算模式,可为none/sum/mean
nn.TripletMarginLoss
功能 计算三元组损失,人脸验证中常用
主要参数
p 范数的阶 默认为2
margin 边界值
reduction 计算模式,可为none/sum/mean
nn.HingeEmbeddingLoss
功能 计算两个输入的相似性,常用于非线性embedding和半监督学习
特别注意 输入x应为两个输入之差的绝对值
主要参数
margin 边界值
reduction 计算模式,可为none/sum/mean
nn.CosineEmbeddingLoss
功能 采用余弦相似度计算两个输入的相似性
主要参数
margin 可取值[-1,1],推荐为[0.0,5]
reduction 计算模式,可为none/sum/mean
nn.CTCLoss
功能 计算CTC损失 解决时序类数据的分类
(Connectionist Temporal Classification)
主要参数
blank blank label
zero_infinity 无穷大的值 或 梯度置0
reduction 计算模式,可为none/sum/mean
# -*- coding: utf-8 -*-
"""
nn.L1Loss
nn.MSELoss
nn.SmoothL1Loss
nn.PoissonNLLLoss
nn.KLDivLoss
nn.MarginRankingLoss
nn.MultiLabelMarginLoss
nn.SoftMarginLoss
nn.MultiLabelSoftMarginLoss
nn.MultiMarginLoss
nn.TripletMarginLoss
nn.HingeEmbeddingLoss
nn.CosineEmbeddingLoss
nn.CTCLoss
"""
import torch
import torch.nn as nn
import torch.nn.functional as F
import matplotlib.pyplot as plt
import numpy as np
from tools.common_tools import set_seed
set_seed(1) # 设置随机种子
# ------------------------------------------------- 5 L1 loss ----------------------------------------------
flag = 0
# flag = 1
if flag:
inputs = torch.ones((2, 2))
target = torch.ones((2, 2)) * 3
loss_f = nn.L1Loss(reduction='none')
loss = loss_f(inputs, target)
print("input:{}\ntarget:{}\nL1 loss:{}".format(inputs, target, loss))
# ------------------------------------------------- 6 MSE loss ----------------------------------------------
loss_f_mse = nn.MSELoss(reduction='none')
loss_mse = loss_f_mse(inputs, target)
print("MSE loss:{}".format(loss_mse))
# ------------------------------------------------- 7 Smooth L1 loss ----------------------------------------------
flag = 0
# flag = 1
if flag:
inputs = torch.linspace(-3, 3, steps=500)
target = torch.zeros_like(inputs)
loss_f = nn.SmoothL1Loss(reduction='none')
loss_smooth = loss_f(inputs, target)
loss_l1 = np.abs(inputs.numpy())
plt.plot(inputs.numpy(), loss_smooth.numpy(), label='Smooth L1 Loss')
plt.plot(inputs.numpy(), loss_l1, label='L1 loss')
plt.xlabel('x_i - y_i')
plt.ylabel('loss value')
plt.legend()
plt.grid()
plt.show()
# ------------------------------------------------- 8 Poisson NLL Loss ----------------------------------------------
flag = 0
# flag = 1
if flag:
inputs = torch.randn((2, 2))
target = torch.randn((2, 2))
loss_f = nn.PoissonNLLLoss(log_input=True, full=False, reduction='none')
loss = loss_f(inputs, target)
print("input:{}\ntarget:{}\nPoisson NLL loss:{}".format(inputs, target, loss))
# --------------------------------- compute by hand
flag = 0
# flag = 1
if flag:
idx = 0
loss_1 = torch.exp(inputs[idx, idx]) - target[idx, idx]*inputs[idx, idx]
print("第一个元素loss:", loss_1)
# ------------------------------------------------- 9 KL Divergence Loss ----------------------------------------------
flag = 0
# flag = 1
if flag:
inputs = torch.tensor([[0.5, 0.3, 0.2], [0.2, 0.3, 0.5]])
inputs_log = torch.log(inputs)
target = torch.tensor([[0.9, 0.05, 0.05], [0.1, 0.7, 0.2]], dtype=torch.float)
loss_f_none = nn.KLDivLoss(reduction='none')
loss_f_mean = nn.KLDivLoss(reduction='mean')
loss_f_bs_mean = nn.KLDivLoss(reduction='batchmean')
loss_none = loss_f_none(inputs, target)
loss_mean = loss_f_mean(inputs, target)
loss_bs_mean = loss_f_bs_mean(inputs, target)
print("loss_none:\n{}\nloss_mean:\n{}\nloss_bs_mean:\n{}".format(loss_none, loss_mean, loss_bs_mean))
# --------------------------------- compute by hand
flag = 0
# flag = 1
if flag:
idx = 0
loss_1 = target[idx, idx] * (torch.log(target[idx, idx]) - inputs[idx, idx])
print("第一个元素loss:", loss_1)
# ---------------------------------------------- 10 Margin Ranking Loss --------------------------------------------
flag = 0
# flag = 1
if flag:
x1 = torch.tensor([[1], [2], [3]], dtype=torch.float)
x2 = torch.tensor([[2], [2], [2]], dtype=torch.float)
target = torch.tensor([1, 1, -1], dtype=torch.float)
loss_f_none = nn.MarginRankingLoss(margin=0, reduction='none')
loss = loss_f_none(x1, x2, target)
print(loss)
# ---------------------------------------------- 11 Multi Label Margin Loss -----------------------------------------
flag = 0
# flag = 1
if flag:
x = torch.tensor([[0.1, 0.2, 0.4, 0.8]])
y = torch.tensor([[0, 3, -1, -1]], dtype=torch.long)
loss_f = nn.MultiLabelMarginLoss(reduction='none')
loss = loss_f(x, y)
print(loss)
# --------------------------------- compute by hand
flag = 0
# flag = 1
if flag:
x = x[0]
item_1 = (1-(x[0] - x[1])) + (1 - (x[0] - x[2])) # [0]
item_2 = (1-(x[3] - x[1])) + (1 - (x[3] - x[2])) # [3]
loss_h = (item_1 + item_2) / x.shape[0]
print(loss_h)
# ---------------------------------------------- 12 SoftMargin Loss -----------------------------------------
flag = 0
# flag = 1
if flag:
inputs = torch.tensor([[0.3, 0.7], [0.5, 0.5]])
target = torch.tensor([[-1, 1], [1, -1]], dtype=torch.float)
loss_f = nn.SoftMarginLoss(reduction='none')
loss = loss_f(inputs, target)
print("SoftMargin: ", loss)
# --------------------------------- compute by hand
flag = 0
# flag = 1
if flag:
idx = 0
inputs_i = inputs[idx, idx]
target_i = target[idx, idx]
loss_h = np.log(1 + np.exp(-target_i * inputs_i))
print(loss_h)
# ---------------------------------------------- 13 MultiLabel SoftMargin Loss -----------------------------------------
flag = 0
# flag = 1
if flag:
inputs = torch.tensor([[0.3, 0.7, 0.8]])
target = torch.tensor([[0, 1, 1]], dtype=torch.float)
loss_f = nn.MultiLabelSoftMarginLoss(reduction='none')
loss = loss_f(inputs, target)
print("MultiLabel SoftMargin: ", loss)
# --------------------------------- compute by hand
flag = 0
# flag = 1
if flag:
i_0 = torch.log(torch.exp(-inputs[0, 0]) / (1 + torch.exp(-inputs[0, 0])))
i_1 = torch.log(1 / (1 + torch.exp(-inputs[0, 1])))
i_2 = torch.log(1 / (1 + torch.exp(-inputs[0, 2])))
loss_h = (i_0 + i_1 + i_2) / -3
print(loss_h)
# ---------------------------------------------- 14 Multi Margin Loss -----------------------------------------
flag = 0
# flag = 1
if flag:
x = torch.tensor([[0.1, 0.2, 0.7], [0.2, 0.5, 0.3]])
y = torch.tensor([1, 2], dtype=torch.long)
loss_f = nn.MultiMarginLoss(reduction='none')
loss = loss_f(x, y)
print("Multi Margin Loss: ", loss)
# --------------------------------- compute by hand
flag = 0
# flag = 1
if flag:
x = x[0]
margin = 1
i_0 = margin - (x[1] - x[0])
# i_1 = margin - (x[1] - x[1])
i_2 = margin - (x[1] - x[2])
loss_h = (i_0 + i_2) / x.shape[0]
print(loss_h)
# ---------------------------------------------- 15 Triplet Margin Loss -----------------------------------------
flag = 0
# flag = 1
if flag:
anchor = torch.tensor([[1.]])
pos = torch.tensor([[2.]])
neg = torch.tensor([[0.5]])
loss_f = nn.TripletMarginLoss(margin=1.0, p=1)
loss = loss_f(anchor, pos, neg)
print("Triplet Margin Loss", loss)
# --------------------------------- compute by hand
flag = 0
# flag = 1
if flag:
margin = 1
a, p, n = anchor[0], pos[0], neg[0]
d_ap = torch.abs(a-p)
d_an = torch.abs(a-n)
loss = d_ap - d_an + margin
print(loss)
# ---------------------------------------------- 16 Hinge Embedding Loss -----------------------------------------
flag = 0
# flag = 1
if flag:
inputs = torch.tensor([[1., 0.8, 0.5]])
target = torch.tensor([[1, 1, -1]])
loss_f = nn.HingeEmbeddingLoss(margin=1, reduction='none')
loss = loss_f(inputs, target)
print("Hinge Embedding Loss", loss)
# --------------------------------- compute by hand
flag = 0
# flag = 1
if flag:
margin = 1.
loss = max(0, margin - inputs.numpy()[0, 2])
print(loss)
# ---------------------------------------------- 17 Cosine Embedding Loss -----------------------------------------
flag = 0
# flag = 1
if flag:
x1 = torch.tensor([[0.3, 0.5, 0.7], [0.3, 0.5, 0.7]])
x2 = torch.tensor([[0.1, 0.3, 0.5], [0.1, 0.3, 0.5]])
target = torch.tensor([[1, -1]], dtype=torch.float)
loss_f = nn.CosineEmbeddingLoss(margin=0., reduction='none')
loss = loss_f(x1, x2, target)
print("Cosine Embedding Loss", loss)
# --------------------------------- compute by hand
flag = 0
# flag = 1
if flag:
margin = 0.
def cosine(a, b):
numerator = torch.dot(a, b)
denominator = torch.norm(a, 2) * torch.norm(b, 2)
return float(numerator/denominator)
l_1 = 1 - (cosine(x1[0], x2[0]))
l_2 = max(0, cosine(x1[0], x2[0]))
print(l_1, l_2)
# ---------------------------------------------- 18 CTC Loss -----------------------------------------
# flag = 0
flag = 1
if flag:
T = 50 # Input sequence length
C = 20 # Number of classes (including blank)
N = 16 # Batch size
S = 30 # Target sequence length of longest target in batch
S_min = 10 # Minimum target length, for demonstration purposes
# Initialize random batch of input vectors, for *size = (T,N,C)
inputs = torch.randn(T, N, C).log_softmax(2).detach().requires_grad_()
# Initialize random batch of targets (0 = blank, 1:C = classes)
target = torch.randint(low=1, high=C, size=(N, S), dtype=torch.long)
input_lengths = torch.full(size=(N,), fill_value=T, dtype=torch.long)
target_lengths = torch.randint(low=S_min, high=S, size=(N,), dtype=torch.long)
ctc_loss = nn.CTCLoss()
loss = ctc_loss(inputs, target, input_lengths, target_lengths)
print("CTC loss: ", loss)
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