[机器学习]用Java实现梯度下降

系统管理员 2022-05-31 10:19 171阅读 0赞

这是在coursea的解释 多元的梯度下降 运算过程

![70][]

实际也就是求偏导数

本测试用例为2元

但适用于多元的数据

数据如下

1,2,3

代码如下

package hello;
    
    import java.io.BufferedReader;
    import java.io.File;
    import java.io.FileReader;
    import java.io.IOException;
    import java.util.List;
    import java.util.Vector;
    
    public class GradientDescent {
    	public static Double[] getTheta(List<Double[]> X, Double[] y) {
    		//初始化长度
    		int m = y.length;
    		//初始化theta
    		Double[] theta = new Double[X.size()];
    		double a = 0.001;
    		for (int i = 0; i < theta.length; i++) {
    			theta[i] = 0.0;
    		}
    		//迭代150000次
    		for (int i = 0; i < 150000; i++) {
    			//初始化temp,做替换用
    			Double[] temp = new Double[theta.length];
    			for (int j = 0; j < temp.length; j++) {
    				temp[j] = 0.0;
    			}
    			for (int j = 0; j < m; j++) {
    				Double sum = 0.0;
    				for (int k = 0; k < theta.length; k++) {
    					//在二元图形中,这里相当于k*x+b*1,三元相当于a*x+b*y+c*1,以此类推
    					sum += theta[k] * X.get(k)[j];
    				}
    				sum = sum - y[j];
    				for (int k = 0; k < theta.length; k++) {
    					temp[k] += sum * X.get(k)[j];
    				}
    			}
    			for (int j = 0; j < theta.length; j++) {
    				//一起替换 同时更新
    				theta[j] -= a / m * temp[j];
    			}
    		}
    		return theta;
    	}
    
    	public static void main(String[] args) throws IOException {
    		Double[] x1 = GradientDescent.read("C:/Users/ojama/Desktop/testX.txt");
    		Double[] y = GradientDescent.read("C:/Users/ojama/Desktop/testY.txt");
    		int m = y.length;
    		Double[] x0 = new Double[m];
    		for (int i = 0; i < x0.length; i++) {
    			x0[i] = 1.0;
    		}
    		List<Double[]> X = new Vector<Double[]>();
    		X.add(x0);
    		X.add(x1);
    		Double[] theta = GradientDescent.getTheta(X, y);
    		for (int i = 0; i < theta.length; i++) {
    			System.out.println(theta[i]);
    		}
    	}
    
    	public static Double[] read(String fileName) throws IOException {
    		File file = new File(fileName);
    		FileReader fileReader = new FileReader(file);
    		BufferedReader reader = new BufferedReader(fileReader);
    		StringBuilder sb = new StringBuilder();
    		String str = reader.readLine();
    		while (str != null) {
    			sb.append(str);
    			str = reader.readLine();
    		}
    		reader.close();
    		fileReader.close();
    		String[] X0 = sb.toString().replace(" ", "").split(",");
    		Double[] x0 = new Double[X0.length];
    		for (int i = 0; i < x0.length; i++) {
    			x0[i] = Double.parseDouble(X0[i]);
    		}
    		return x0;
    	}
    }

运行结果：

![70 1][]  
theta0约等于0theta1约等于1;

虽然有一定的误差 但已经足够精确了。

[70]: /images/20220531/11371e40fd794c33b7f51f1202fc7e05.png
[70 1]: /images/20220531/643c65130e964216aed21ccbc8b3a505.png