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
$l_{n}=\left|x_{n}-y_{n}\right|$

nn.MSELoss

功能 计算inputs 与 target 之差的平方
$l_{n}=\left(x_{n}-y_{n}\right)^{2}$
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
$\operatorname{loss}(x, y)=\frac{1}{n} \sum_{i} z_{i}$
$z_{i}=\left\{\begin{array}{ll} 0.5\left(x_{i}-y_{i}\right)^{2}, & \text { if }\left|x_{i}-y_{i}\right|<1 \\ \left|x_{i}-y_{i}\right|-0.5, & \text { otherwise } \end{array}\right.$

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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$loss (input, target) = input - target * log(input+eps)$

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
$\begin{aligned} D_{K L}(P \| Q)=E_{x-p}\left[\log \frac{P(x)}{Q(x)}\right] &=E_{x-p}[\log P(x)-\log Q(x)] \\ &=\sum_{i=1}^{N} \mathrm{P}\left(x_{i}\right)\left(\log P\left(x_{i}\right)-\log Q\left(x_{i}\right)\right) \end{aligned}$
$l_{n}=y_{n} \cdot\left(\log y_{n}-x_{n}\right)$

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
$\operatorname{loss}(x, y)=\max (0,-y *(x 1-x 2)+\text { margin })$
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
$\operatorname{loss}(x, y)=\sum_{i j} \frac{\max (0,1-(x[y[j]]-x[i]))}{x \cdot \operatorname{size}(0)}$

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
$\operatorname{loss}(x, y)=\sum_{i} \frac{\log (1+\exp (-y[i] * x[i]))}{x \cdot \operatorname{nelement} 0}$
#·
reduction 计算模式，可为none/sum/mean
$\operatorname{loss}(x, y)=-\frac{1}{C} * \sum_{i} y[i] * \log \left((1+\exp (-x[i]))^{-1}\right)+(1-y[i]) * \log \left(\frac{\exp (-x[i])}{(1+\exp (-x[i]))}\right)$

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
$\operatorname{loss}(x, y)=\frac{\left.\sum_{i} \max (0, \operatorname{margin}-x[y]+x[i])\right)^{p}}{x \cdot \operatorname{size}(0)}$

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
$\begin{array}{c} L(a, p, n)=\max \left\{d\left(a_{i}, p_{i}\right)-d\left(a_{i}, n_{i}\right)+\text { margin, } 0\right\} \\ \qquad d\left(x_{i}, y_{i}\right)=\left\|\mathbf{x}_{i}-\mathbf{y}_{i}\right\|_{p} \end{array}$

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
$l_{n}=\left\{\begin{array}{ll} x_{n}, & \text { if } y_{n}=1 \\ \max \left\{0, \Delta-x_{n}\right\}, & \text { if } y_{n}=-1 \end{array}\right.$

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
$\operatorname{loss}(x, y)=\left\{\begin{array}{ll} 1-\cos \left(x_{1}, x_{2}\right), & \text { if } y=1 \\ \max \left(0, \cos \left(x_{1}, x_{2}\right)-\operatorname{margin}\right), & \text { if } y=-1 \end{array}\right.$
$\cos (\theta)=\frac{A \cdot B}{\|A\|\|B\|}=\frac{\sum_{i=1}^{n} A_{i} \times B_{i}}{\sqrt{\sum_{i=1}^{n}\left(A_{i}\right)^{2}} \times \sqrt{\sum_{i=1}^{n}\left(B_{i}\right)^{2}}}$
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)