"""
pytorch CrossEntropyLoss 用法
"""
import torch
import torch.nn as nn
import math
loss = nn.CrossEntropyLoss()
input = torch.randn(1, 5, requires_grad=True)
target = torch.empty(1, dtype=torch.long).random_(5)
output = loss(input, target)

print("输入为5类:")
print(input)
print("要计算loss的类别:")
print(target)
print("计算loss的结果:")
print(output)

first = 0
for i in range(1):
    first -= input[i][target[i]]
second = 0
for i in range(1):
    for j in range(5):
        second += math.exp(input[i][j])
res = 0
res += first +math.log(second)
print("自己的计算结果：")
print(res)