softmax代码实现，代码原理供参考
import torchfrom IPython import displayfrom d2l import torch as d2limport torch.utils.data.dataloaderfrom matplotlib import pyplot as plt# import pylabbatch_size=64train_iter,test_iter=d2l.load_data_fashion_mnist(batch_size) #训练集和测试集的迭代器num_inpu.
