torch.nn.Linear()

import torch

x = torch.randn(128, 20) # 输入的维度是（128，20）
m = torch.nn.Linear(20, 30) # 20, 30是指维度
output = m(x)
print('m.weight.shape:\n', m.weight.shape)
print('m.bias.shape:\n', m.bias.shape)
print('output.shape:\n', output.shape)

m.weight.shape:
  torch.Size([30, 20])
m.bias.shape:
 torch.Size([30])
output.shape:
 torch.Size([128, 30])

为什么m.weight.shape=(30, 20)?

因为线性变换的公式是：
$$y=x{A}^T+b$$
先生成一个（30， 20）的weight，实际运算中再转置，这样就能和x做矩阵乘法了。

Reference:
https://blog.youkuaiyun.com/m0_37586991/article/details/87861418