1 算法介绍

2 代码实现

2.1 比较复杂的代码，函数自己写。

# -*- coding:utf-8 -*-
from matplotlib import pyplot as plt
from mxnet import autograd, nd
import matplotlib as mpl
import random

mpl.rcParams["font.sans-serif"] = ['Fangsong']
mpl.rcParams['axes.unicode_minus'] = False


def visualization(features, labels):
    plt.scatter(features[:, 1].asnumpy(), labels.asnumpy())
    plt.show()


def data_iter(batch_size, features, labels):
    num_examples = len(features)
    indices = list(range(num_examples))
    random.shuffle(indices)  # 读取样本是随机的
    for i in range(0, num_examples, batch_size):
        j = nd.array(indices[i: min(i + batch_size, num_examples)])
        yield features.take(j), labels.take(j)  # take函数根据索引返回函数对应元素


def linreg(x, w, b):
    return nd.dot(x, w) + b


def squared_loss(y_hat, y):
    return (y_hat - y.reshape(y_hat.shape)) ** 2 / 2


def sgd(params, lr, batch_size):
    for params in params:
        params[:] = params - lr * params.grad / batch_size


if __name__ == '__main__':
    num_inputs = 2
    num_examples = 1000
    true_w = [2, -3.4]
    true_b = 4.2
    features = nd.random.normal(scale=1, shape=(num_examples, num_inputs))
    labels = true_w[0] * features[:, 0] + true_w[1] * features[:, 1] + true_b
    # visualization(features, labels)

    batch_size = 10
    # for x, y in data_iter(batch_size, features, labels):
    #     print(x, y)
    #     break

    w = nd.random.normal(scale=0.01, shape=(num_inputs, 1))
    b = nd.zeros(shape=(1,))

    w.attach_grad()
    b.attach_grad()

    lr = 0.03
    num_epoch = 30
    net = linreg
    loss = squared_loss

    for epoch in range(num_epoch):
        for x,y in data_iter(batch_size, features, labels):
            with autograd.record():
                l = loss(net(x, w, b), y)
            l.backward()
            sgd([w, b], lr, batch_size)
        train_l = loss(net(features, w, b), labels)
        print('epoch %d, loss: %lf'%(epoch+1, train_l.mean().asnumpy()))
    print(true_w, true_b)
    print(w, b)

2.2 比较简洁的代码，都是调用的包。

# -*- coding:utf-8 -*-
from matplotlib import pyplot as plt
from mxnet import autograd, nd, init
from mxnet.gluon import data as gdata
import matplotlib as mpl
from mxnet.gluon import nn
from mxnet import gluon
from mxnet.gluon import loss as gloss
import random

mpl.rcParams["font.sans-serif"] = ['Fangsong']
mpl.rcParams['axes.unicode_minus'] = False


def visualization(features, labels):
    plt.scatter(features[:, 1].asnumpy(), labels.asnumpy())
    plt.show()


if __name__ == '__main__':
    num_inputs = 2
    num_examples = 1000
    true_w = [2, -3.4]
    true_b = 4.2
    features = nd.random.normal(scale=1, shape=(num_examples, num_inputs))
    labels = true_w[0] * features[:, 0] + true_w[1] * features[:, 1] + true_b
    # visualization(features, labels)

    batch_size = 10
    dataset = gdata.ArrayDataset(features, labels)
    data_iter = gdata.DataLoader(dataset, batch_size, shuffle=True)

    lr = 0.03
    num_epoch = 30
    net = nn.Sequential()
    net.add(nn.Dense(1))
    net.initialize(init.Normal(sigma=0.01))
    loss = gloss.L2Loss()
    trainer = gluon.Trainer(net.collect_params(), 'sgd', {'learning_rate': 0.03})

    for epoch in range(num_epoch):
        for x, y in data_iter:
            with autograd.record():
                l = loss(net(x), y)
            l.backward()
            trainer.step(batch_size)
        l=loss(net(features), labels)
        print('epoch %d, loss: %lf' % (epoch + 1, l.mean().asnumpy()))
    dense = net[0]
    print(true_w, dense.weight.data())
    print(true_b, dense.bias.data())