MXNet动手学深度学习笔记:卷积神经网络实现
2018-05-09 23:42
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#coding:utf-8 ''' 卷积神经网络 ''' import mxnet as mx from mxnet.gluon import nn from mxnet import ndarray as nd from mxnet import gluon try: ctx = mx.gpu() _ = nd.zeros((1,),ctx = ctx) except: ctx = mx.cpu() def transform(data,label): return data.astype('float32') / 255,label.astype('float32') mnist_train = gluon.data.vision.FashionMNIST(train=True,transform=transform) mnist_test = gluon.data.vision.FashionMNIST(train=False,transform=transform) # 显示样本的形状和标号 data,label = mnist_train[0] print('shape:',data.shape,',label:',label) # def show_images(images): # n = images.shape[0] # _,figs = plt.subplots(1,n,figsize=(15,15)) # for i in range(n): # figs[i].imshow(images[i].reshape((28,28)).asnumpy()) # figs[i].axes.get_xaxis().set_visible(False) # figs[i].axes.get_yaxis().set_visible(False) # plt.show() def get_text_labels(label): text_labels = [ 't-shirt','trouser','pullover','dress','coat', 'sandal','shirt','sneaker','bag','ankle boot' ] return [text_labels[int(i)] for i in label] # 显示数据 # data,label = mnist_train[0:9] # show_images(data) # print(get_text_labels(label)) # 读取数据 batch_size = 64 train_data = gluon.data.DataLoader(mnist_train,batch_size,shuffle=True) test_data = gluon.data.DataLoader(mnist_test,batch_size,shuffle=False) print('use contex:',ctx) weight_scale = 0.01 # 输出通道 = 20,卷积核 kernel=(5,5) W1 = nd.random_normal(shape=(20,1,5,5),scale=weight_scale,ctx=ctx) b1 = nd.zeros(W1.shape[0],ctx=ctx) # 输出通道=50,卷积核 kernel=(3,3) W2 = nd.random_normal(shape=(50,20,3,3),scale=weight_scale,ctx=ctx) b2 = nd.zeros(W2.shape[0],ctx=ctx) # 输出维度=128 W3 = nd.random_normal(shape=(1250,128),scale=weight_scale,ctx=ctx) b3 = nd.zeros(W3.shape[1],ctx=ctx) # 输出维度=10 W4 = nd.random_normal(shape=(W3.shape[1],10),scale=weight_scale,ctx=ctx) b4 = nd.zeros(W4.shape[1],ctx=ctx) params = [W1,b1,W2,b2,W3,b3,W4,b4] for param in params: param.attach_grad() # 定义卷积神经网络模型 # 卷积层-激活层-池化层,然后转换成2D矩阵输出给后面的全连接层 def net(X,verbose=False): X = X.as_in_context(W1.context) # 第一层卷积 h1_conv = nd.Convolution(data=X,weight=W1,bias=b1, kernel=W1.shape[2:],num_filter=W1.shape[0]) # 第一层激活函数 h1_activation = nd.relu(h1_conv) # 第一层池化层 h1 = nd.Pooling(data=h1_activation,pool_type='max',kernel=(2,2),stride=(2,2)) # 第二层卷积层 h2_conv = nd.Convolution(data=h1,weight=W2,bias=b2, kernel=W2.shape[2:],num_filter=W2.shape[0]) h2_activation = nd.relu(h2_conv) h2 = nd.Pooling(data=h2_activation,pool_type='max',kernel=(2,2)) h2 = nd.flatten(h2) # 第一层全连接 h3_linear = nd.dot(h2,W3) + b3 h3 = nd.relu(h3_linear) # 第二层全连接 h4_linear = nd.dot(h3,W4) + b4 if verbose: print('1st conv block:', h1.shape) print('2nd conv block:', h2.shape) print('1st dense:', h3.shape) print('2nd dense:', h4_linear.shape) print('output:', h4_linear) return h4_linear # 定义精度计算 def accuracy(output,label): return nd.mean(output.argmax(axis=1) == label).asscalar() # 估计模型精度 def evaluate_accuracy(data_iterator,net,ctx): acc = 0 for data,label in data_iterator: label = label.as_in_context(ctx) output = net(data) acc += accuracy(output,label) return acc / len(data_iterator) # 优化器 def SGD(params,lr): for param in params: param[:] = param - lr * param.grad # 训练 softmax_cross_entropy = gluon.loss.SoftmaxCrossEntropyLoss() learning_rate = .2 epochs = 5 for epoch in range(epochs): train_loss = 0.0 train_acc = 0.0 for data,label in train_data: # 复制到GPU label = label.as_in_context(ctx) with mx.autograd.record(): output = net(data) loss = softmax_cross_entropy(output,label) loss.backward() SGD(params,learning_rate / batch_size) train_loss += nd.mean(loss).asscalar() train_acc += accuracy(output,label) test_acc = evaluate_accuracy(test_data, net, ctx) print("Epoch %d. Loss: %f, Train acc %f, Test acc %f" % (epoch, train_loss/len(train_data), train_acc/len(train_data), test_acc))
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