Pytorch实战（3）----分类

一、分类任务：

将以下两类分开。

创建数据代码：

# make fake data
n_data = torch.ones(100, 2)
x0 = torch.normal(2*n_data, 1)      # class0 x data (tensor), shape=(100, 2)
y0 = torch.zeros(100)               # class0 y data (tensor), shape=(100, 1)
x1 = torch.normal(-2*n_data, 1)     # class1 x data (tensor), shape=(100, 2)
y1 = torch.ones(100)                # class1 y data (tensor), shape=(100, 1)
x = torch.cat((x0, x1), 0).type(torch.FloatTensor)  # shape (200, 2) FloatTensor = 32-bit floating
y = torch.cat((y0, y1), ).type(torch.LongTensor)    # shape (200,) LongTensor = 64-bit integer

# torch can only train on Variable, so convert them to Variable
x, y = Variable(x), Variable(y)

plt.scatter(x.data.numpy()[:, 0], x.data.numpy()[:, 1], c=y.data.numpy(), s=100, lw=0, cmap='RdYlGn')
plt.show()

二、步骤

1. 导入包

2. 创建模型

3. 设置优化器和损失函数

4. 训练模型

三、代码：

导入包：

import torch
from torch.autograd import Variable
import torch.nn.functional as F
import matplotlib.pyplot as plt
%matplotlib inline

torch.manual_seed(1)    # reproducible

创建模型：

class Net(torch.nn.Module):
    def __init__(self, n_feature, n_hidden, n_output):
        super(Net, self).__init__()
        self.hidden = torch.nn.Linear(n_feature, n_hidden)   # hidden layer
        self.out = torch.nn.Linear(n_hidden, n_output)   # output layer

    def forward(self, x):
        x = F.relu(self.hidden(x))      # activation function for hidden layer
        x = self.out(x)
        return x

设置优化器和损失函数

#输入的x为2维张量，输出有两类
net = Net(n_feature=2, n_hidden=10, n_output=2)     # define the network
print(net)  # net architecture

# Loss and Optimizer
# Softmax is internally computed.
# Set parameters to be updated.
optimizer = torch.optim.SGD(net.parameters(), lr=0.02)
loss_func = torch.nn.CrossEntropyLoss()  # the target label is NOT an one-hotted

训练模型并画图展示

plt.ion()   # something about plotting
plt.show()

for t in range(100):
    out = net(x)                 # input x and predict based on x
    loss = loss_func(out, y)     # must be (1. nn output, 2. target), the target label is NOT one-hotted

    optimizer.zero_grad()   # clear gradients for next train
    loss.backward()         # backpropagation, compute gradients
    optimizer.step()        # apply gradients
    
    if t % 10 == 0 or t in [3, 6]:
        # plot and show learning process
        plt.cla()
        _, prediction = torch.max(F.softmax(out), 1)  #这里是得到softmax之后最大概率的y预测值。
        pred_y = prediction.data.numpy().squeeze()
        print(pred_y)
        target_y = y.data.numpy()
        plt.scatter(x.data.numpy()[:, 0], x.data.numpy()[:, 1], c=pred_y, s=100, lw=0, cmap='RdYlGn')
        accuracy = sum(pred_y == target_y)/200.
        plt.text(1.5, -4, 'Accuracy=%.2f' % accuracy, fontdict={'size': 20, 'color':  'red'})
        plt.show()
#         plt.pause(0.1)

plt.ioff()

结果展示：