使用PyTorch框架结合Visdom工具实现神经网络模型（尤其是CNN结构）来完成手写字体分类任务。

    class Nueralnetwork(nn.Module):
    def __init__(self,in_dim,hidden1,hidden2,out_dim):
        super(Nueralnetwork, self).__init__()
        self.layer1 = nn.Linear(in_dim,hidden1)
        self.layer2 = nn.Linear(hidden1,hidden2)
        self.layer3 = nn.Linear(hidden2,out_dim)
    
    def forward(self,x):
        x = self.layer1(x)
        x = self.layer2(x)
        x = self.layer3(x)
        return x
    
    net = Nueralnetwork(28*28,200,100,1