大家好，又见面了，我是全栈君，今天给大家准备了Idea注册码。

需求:

• 从零和使用mxnet实现dropout

数据集：

• 使用load_digits()手写数字数据集

要求：

• 使用1个掩藏层n_hidden1 = 36，激活函数为relu，损失函数为softmax交叉熵损失函数

注意：

• drop函数的实现方法
• 训练和测试时drop的区别

1.从零实现dropout

from sklearn import datasets
from mxnet import gluon,nd,autograd,init
from mxnet.gluon import nn,data as gdata,loss as gloss,trainer

# 加载数据集
digits = datasets.load_digits()
features,labels = nd.array(digits['data']),nd.array(digits['target'])
print(features.shape,labels.shape)
labels_onehot = nd.one_hot(labels,10)
print(labels_onehot.shape)

(1797, 64) (1797,)
(1797, 10)

class NeuroNet:
    def __init__(self,n_inputs,n_hidden1,n_outputs):
        hidden_layer = Layer(n_inputs,n_hidden1)
        output_layer = Layer(n_hidden1,n_outputs)
        self.layers = [hidden_layer,output_layer]
        
        for layer in self.layers:
            for param in layer.params:
                param.attach_grad()
    
    def softmax(self,x):
        step1 = x.exp()
        step2 = step1 / step1.sum(axis=1,keepdims=True)
        return step2
    
    def softmaxCrossEntropyLoss(self,y_pred,y):
        step1 = -y * y_pred.log()
        step2 = step1.sum(axis=1)
        loss = step2.sum(axis=0) / len(y)
        return loss
        
    def drop(self,x,drop_probability,train=True):
        '''
        神经元被丢弃的概率为p
        '''
        if train:
            mask = nd.random.uniform(0,1,shape=x.shape,dtype='float32') > drop_probability
            return mask * x / (1 - drop_probability)
        else:
            return x
        
    def forward(self,x,train=True):
        for layer in self.layers[:-1]:
            step1 = layer.forward(x)
            step2 = self.drop(step1,0.2,train)
            x = step2
        output_layer = self.layers[-1]
        return self.softmax(output_layer.forward(x))
    
    def sgd(self,learning_rate,batch_size):
        '''
        使用随机梯度下降更新所有权重和偏置
        '''
        for layer in self.layers:
            layer.sgd(learning_rate,batch_size)
                
    def dataIter(self,x,y,batch_size):
        dataset = gdata.ArrayDataset(x,y)
        return gdata.DataLoader(dataset,batch_size,shuffle=True)
    
    def fit(self,x,y,epoches,batch_size,learning_rate):
        for epoch in range(epoches):
            for x_batch,y_batch in self.dataIter(x,y,batch_size):
                with autograd.record():
                    y_pred = self.forward(x_batch,train=True)
                    loss = self.softmaxCrossEntropyLoss(y_pred,y_batch)
                loss.backward()
                self.sgd(learning_rate,batch_size)
            if epoch % 50 == 0:
                y_pred_all = self.forward(x,train=False)
                loss_all = self.softmaxCrossEntropyLoss(y_pred_all,y)
                accuracy_score = self.accuracyScore(y_pred_all,y)
                print('epoch:{},loss:{},accuracy:{}'.format(epoch+50,loss_all,accuracy_score))
            
    def predict(self,x):
        y_pred = self.forward(x)
        return y_pred.argmax(axis=0)
    
    def accuracyScore(self,y_pred,y):
        acc_sum = (y_pred.argmax(axis=1) == y.argmax(axis=1)).sum().asscalar()
        return acc_sum / len(y)
        
class Layer:
    def __init__(self,n_inputs,n_outputs):
        weight = nd.random.normal(scale=0.01,shape=(n_inputs,n_outputs))
        bias = nd.zeros(shape=(n_outputs))
        self.params = [weight,bias]
    
    def relu(self,x):
        return nd.maximum(x,0)
    
    def forward(self,x):
        step1 = nd.dot(x,self.params[0]) + self.params[1]
        return self.relu(step1)
    
    def sgd(self,learning_rate,batch_size):
        for param in self.params:
            param[:] = param - learning_rate * param.grad / batch_size 
            
    def print_params(self):
        for param in self.params:
            print(param)

net = NeuroNet(64,36,10)
net.fit(features,labels_onehot,epoches=500,batch_size=200,learning_rate=0.5)

epoch:50,loss:
[2.2988722]
<NDArray 1 @cpu(0)>,accuracy:0.18308291597106288
epoch:100,loss:
[1.4126126]
<NDArray 1 @cpu(0)>,accuracy:0.7395659432387313
epoch:150,loss:
[0.46316707]
<NDArray 1 @cpu(0)>,accuracy:0.9259877573734001
epoch:200,loss:
[0.24678323]
<NDArray 1 @cpu(0)>,accuracy:0.9493600445186422
epoch:250,loss:
[0.17839472]
<NDArray 1 @cpu(0)>,accuracy:0.9610461880912632
epoch:300,loss:
[0.14298467]
<NDArray 1 @cpu(0)>,accuracy:0.9688369504730105
epoch:350,loss:
[0.1198809]
<NDArray 1 @cpu(0)>,accuracy:0.9738452977184195
epoch:400,loss:
[0.10388324]
<NDArray 1 @cpu(0)>,accuracy:0.9782971619365609
epoch:450,loss:
[0.0917427]
<NDArray 1 @cpu(0)>,accuracy:0.9827490261547023
epoch:500,loss:
[0.08237094]
<NDArray 1 @cpu(0)>,accuracy:0.9849749582637729

print('预测结果：',net.predict(features[:10]))
print('真实结果：',labels[:10])

预测结果： 
[0. 1. 2. 3. 4. 5. 6. 7. 8. 9.]
<NDArray 10 @cpu(0)>
真实结果： 
[0. 1. 2. 3. 4. 5. 6. 7. 8. 9.]
<NDArray 10 @cpu(0)>

2.使用mxnet实现dropout

n_inputs = 64
n_hiddens = 36
n_outputs = 10

# 定义模型
net = nn.Sequential()
net.add(nn.Dense(n_hiddens,activation='relu'))
net.add(nn.Dropout(rate=0.2))
net.add(nn.Dense(n_outputs))

# 初始化模型
net.initialize(init.Normal(sigma=0.01))

# 损失函数
loss = gloss.SoftmaxCrossEntropyLoss(sparse_label=False)

optimizer = trainer.Trainer(net.collect_params(), 'sgd', {'learning_rate':0.5})

# 训练模型
epoches = 500
batch_size = 200

dataset = gdata.ArrayDataset(features,labels_onehot)
dataIter = gdata.DataLoader(dataset,batch_size,shuffle=True)
for epoch in range(epoches):
    for x_batch,y_batch in dataIter:
        with autograd.record():
            y_pred = net.forward(x_batch)
            l = loss(y_pred, y_batch).sum() / batch_size
        l.backward()
        optimizer.step(batch_size)
    if epoch % 50 == 0:
        y_all_pred = net.forward(features)
        acc_sum = (y_all_pred.argmax(axis=1) == labels_onehot.argmax(axis=1)).sum().asscalar()
        print('epoch:{},loss:{},accuracy:{}'.format(epoch+50,loss(y_all_pred,labels_onehot).sum() / len(labels_onehot),acc_sum/len(y_all_pred)))

epoch:50,loss:
[2.2981045]
<NDArray 1 @cpu(0)>,accuracy:0.16304952698942682
epoch:100,loss:
[0.97166663]
<NDArray 1 @cpu(0)>,accuracy:0.867557039510295
epoch:150,loss:
[0.3836201]
<NDArray 1 @cpu(0)>,accuracy:0.9243183082915971
epoch:200,loss:
[0.24329802]
<NDArray 1 @cpu(0)>,accuracy:0.9449081803005008
epoch:250,loss:
[0.18068495]
<NDArray 1 @cpu(0)>,accuracy:0.9577072899276572
epoch:300,loss:
[0.14546551]
<NDArray 1 @cpu(0)>,accuracy:0.9660545353366722
epoch:350,loss:
[0.1219953]
<NDArray 1 @cpu(0)>,accuracy:0.9727323316638843
epoch:400,loss:
[0.10563282]
<NDArray 1 @cpu(0)>,accuracy:0.9760712298274903
epoch:450,loss:
[0.09357208]
<NDArray 1 @cpu(0)>,accuracy:0.9788536449638287
epoch:500,loss:
[0.08368526]
<NDArray 1 @cpu(0)>,accuracy:0.9816360601001669