21xrx.com
2024-12-22 22:56:03 Sunday
登录
文章检索 我的文章 写文章
Java实现最小二乘法二阶
2023-06-15 12:40:21 深夜i     --     --
Java 最小二乘法 矩阵运算

最小二乘法是一种常用的回归分析方法,用于估计一组数据的线性关系。在Java中,我们可以通过计算矩阵和向量,求解最小二乘法的系数,以达到预测新数据的目的。

下面就是一个简单的Java实现最小二乘法二阶的案例,实现该算法需要用到矩阵运算的基本知识,包括矩阵的转置、乘积、逆矩阵等操作。

代码实现:


import java.util.*;

public class LeastSquares {

  // 计算矩阵的转置

  public double[][] transpose(double[][] A) {

    int m = A.length, n = A[0].length;

    double[][] B = new double[n][m];

    for (int i = 0; i < m; i++)

      for (int j = 0; j < n; j++)

        B[j][i] = A[i][j];

    return B;

  }

  // 计算矩阵的乘积

  public double[][] multiply(double[][] A, double[][] B) {

    int m = A.length, n = B[0].length;

    double[][] C = new double[m][n];

    for (int i = 0; i < m; i++)

      for (int j = 0; j < n; j++)

        for (int k = 0; k < B.length; k++)

          C[i][j] += A[i][k] * B[k][j];

    return C;

  }

  // 计算矩阵的逆

  public double[][] inverse(double[][] A) {

    int n = A.length;

    double[][] B = new double[n][n];

    double[][] C = new double[n][n * 2];

    for (int i = 0; i < n; i++) {

      for (int j = 0; j < n; j++) {

        B[i][j] = A[i][j];

        if (i == j) C[i][j + n] = 1;

      }

    }

    for (int k = 0; k < n; k++) {

      double max = 0; int index = 0;

      for (int i = k; i < n; i++) {

        if (Math.abs(B[i][k]) > max) {

          max = Math.abs(B[i][k]);

          index = i;

        }

      }

      if (index != k) {

        for (int j = 0; j < n; j++) {

          double temp = B[k][j];

          B[k][j] = B[index][j];

          B[index][j] = temp;

          temp = C[k][j + n];

          C[k][j + n] = C[index][j + n];

          C[index][j + n] = temp;

        }

      }

      for (int j = k; j < n; j++) B[k][j] /= max;

      for (int j = 0; j < n; j++) C[k][j + n] /= max;

      for (int i = k + 1; i < n; i++) {

        double factor = B[i][k];

        for (int j = k + 1; j < n; j++) B[i][j] -= factor * B[k][j];

        for (int j = 0; j < n; j++) C[i][j + n] -= factor * C[k][j + n];

      }

    }

    for (int k = n - 1; k >= 0; k--) {

      for (int i = k - 1; i >= 0; i--) {

        double factor = B[i][k];

        for (int j = 0; j < n; j++) C[i][j + n] -= factor * C[k][j + n];

      }

    }

    double[][] D = new double[n][n];

    for (int i = 0; i < n; i++)

      for (int j = 0; j < n; j++)

        D[i][j] = C[i][j + n];

    return D;

  }

  // 计算最小二乘法的系数

  public double[] leastSquares(double[][] X, double[] y) {

    double[][] X1 = new double[X.length][3];

    for (int i = 0; i < X.length; i++) {

      X1[i][0] = 1;

      X1[i][1] = X[i][0];

      X1[i][2] = X[i][0] * X[i][0];

    }

    double[] y1 = Arrays.copyOf(y, y.length);

    double[][] X2 = transpose(X1);

    double[][] X3 = multiply(X2, X1);

    double[][] X4 = inverse(X3);

    double[][] X5 = multiply(X4, X2);

    double[] beta = multiply(X5, y1);

    return beta;

  }

  // 测试

  public static void main(String[] args) {

    double[][] X = {{1}, {2}, {3}, {4}, {5}};

    double[] y = {6, 9, 12, 15, 20};

    LeastSquares ls = new LeastSquares();

    double[] beta = ls.leastSquares(X, y);

    System.out.println("y = " + beta[0] + " + " + beta[1] + "x + " + beta[2] + "x^2");

  }

}

上述代码实现了最小二乘法二阶的算法,它包含了计算矩阵的转置、乘积、逆矩阵等基本操作,以及计算最小二乘法系数的方法leastSquares。

在测试中,我们输入了一个包含五个数据点的二次函数的点值,通过最小二乘法求得该二次函数的系数,最终输出该二次函数的表达式。

  
  

评论区

{{item['qq_nickname']}}
()
回复
回复
    相似文章