了解神经网络原理的同学们应该都知道,隐藏层越多,最终预测结果的准确度越高,但是计算量也越大,在上一篇的基础上,我们手动添加一个隐藏层,代码如下(主要参考自多层感知机 — 从0开始):
from mxnet import gluon from mxnet import ndarray as nd import matplotlib.pyplot as plt import mxnet as mx from mxnet import autograd 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) 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 恤‘, ‘长 裤‘, ‘套头衫‘, ‘裙 子‘, ‘外 套‘, ‘凉 鞋‘, ‘衬 衣‘, ‘运动鞋‘, ‘包 包‘, ‘短 靴‘ ] return [text_labels[int(i)] for i in label] data, label = mnist_train[0:10] print(‘example shape: ‘, data.shape, ‘label:‘, label) show_images(data) print(get_text_labels(label)) batch_size = 256 train_data = gluon.data.DataLoader(mnist_train, batch_size, shuffle=True) test_data = gluon.data.DataLoader(mnist_test, batch_size, shuffle=False) num_inputs = 784 num_outputs = 10 #增加一层包含256个节点的隐藏层 num_hidden = 256 weight_scale = .01 #输入层的参数 W1 = nd.random_normal(shape=(num_inputs, num_hidden), scale=weight_scale) b1 = nd.zeros(num_hidden) #隐藏层的参数 W2 = nd.random_normal(shape=(num_hidden, num_outputs), scale=weight_scale) b2 = nd.zeros(num_outputs) #参数变多了 params = [W1, b1, W2, b2] for param in params: param.attach_grad() #激活函数 def relu(X): return nd.maximum(X, 0) #计算模型 def net(X): X = X.reshape((-1, num_inputs)) #先计算到隐藏层的输出 h1 = relu(nd.dot(X, W1) + b1) #再利用隐藏层计算最终的输出 output = nd.dot(h1, W2) + b2 return output #Softmax和交叉熵损失函数 softmax_cross_entropy = gluon.loss.SoftmaxCrossEntropyLoss() def accuracy(output, label): return nd.mean(output.argmax(axis=1) == label).asscalar() def _get_batch(batch): if isinstance(batch, mx.io.DataBatch): data = batch.data[0] label = batch.label[0] else: data, label = batch return data, label def evaluate_accuracy(data_iterator, net): acc = 0. if isinstance(data_iterator, mx.io.MXDataIter): data_iterator.reset() for i, batch in enumerate(data_iterator): data, label = _get_batch(batch) output = net(data) acc += accuracy(output, label) return acc / (i+1) learning_rate = .5 for epoch in range(5): train_loss = 0. train_acc = 0. for data, label in train_data: with autograd.record(): output = net(data) #使用Softmax和交叉熵损失函数 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) print("Epoch %d. Loss: %f, Train acc %f, Test acc %f" % ( epoch, train_loss / len(train_data), train_acc / len(train_data), test_acc)) data, label = mnist_test[0:10] show_images(data) print(‘true labels‘) print(get_text_labels(label)) predicted_labels = net(data).argmax(axis=1) print(‘predicted labels‘) print(get_text_labels(predicted_labels.asnumpy()))
有变化的地方,都加了注释,主要改动点有5个:
1. 手动添加了1个隐藏层,该层有256个节点
2. 多了一层,所以参数也变多了
3. 计算y=wx+b模型时,就要一层层来算了
4. 将softmax与交叉熵CrossEntropy合并了(这样避免了单独对softmax求导,理论上讲更稳定些)
5. 另外激活函数换成了收敛速度更快的relu(参考:Deep learning系列(七)激活函数 )
运行效果:
相对原始纯手动版本,准确率提升了不少!