[Solved] pytorch CrossEntropyLoss Error: RuntimeError: 1D target tensor expected, multi-target not supported

resolvent

crossentropyloss (predicted value, label) the required input dimensions are:

    1. when there is batch, the predicted value dimension is 2 and the size is

[batch]_ When size, n]

    1. , the dimension of label is 1, and the size is

[batch]_ Size]

    1. when there is no batch, the dimension of the predicted value is 2, the size is

[M, n]

    1. , the dimension of the label is 1, and the size is

[M]

Problem analysis

One case can illustrate:

import torch
import torch.nn as nn
import numpy as np

a = torch.tensor(np.random.random((30, 5)))
b = torch.tensor(np.random.randint(0, 4, (30))).long()
loss = nn.CrossEntropyLoss()

print("a的维度：", a.size()) # torch.Size([30, 5])
print("b的维度：", b.size()) # torch.Size([30])
print(loss(a, b)) # tensor(1.6319, dtype=torch.float64)