Question

这是我的代码：

package algorithms;
import Jama.Matrix;
import java.io.File;
import java.util.Arrays;
public class ThetaGetter {
    //First column is one, second is price and third is BHK
    private static double[][] variables = {
        {1,1130,2},
        {1,1100,2},
        {1,2055,3},
        {1,1047,2},
        {1,1927,3},
        {1,2667,3},
        {1,1146,2},
        {1,2020,3},
        {1,1190,2},
        {1,2165,3},
        {1,1250,2},
        {1,1185,2},
        {1,2825,4},
        {1,1200,2},
        {1,1580,3},
        {1,3200,3},
        {1,715,1},
        {1,1270,2},
        {1,2403,3},
        {1,1465,3},
        {1,1345,2}
    };

    private static double[][] prices = {
        {69.65},
        {60},
        {115},
        {55},
        {140},
        {225},
        {76.78},
        {120},
        {73.11},
        {140},
        {56},
        {79.39},
        {161},
        {73.69},
        {80},
        {145},
        {34.87},
        {77.72},
        {165},
        {98},
        {82}
    };
    private static Matrix X = new Matrix(variables);
    private static Matrix y = new Matrix(prices);
    public static void main(String[] args) {
        File file = new File("theta.dat");
        if(file.exists()){
            System.out.println("Theta has already been calculated!");
            return;
        }
        //inverse(Tra(X)*X)*tra(X)*y
        Matrix transposeX = X.transpose();
        Matrix inverse = X.times(transposeX).inverse();
        System.out.println(y.getArray().length);
        System.out.println(X.getArray().length);
        Matrix test = inverse.times(transposeX);
        Matrix theta = test.times(y);
        System.out.println(Arrays.deepToString(theta.getArray()));
    }
}

这个算法基本上试图取得房价，然后得到一些常数，然后用来猜测房屋价格。但是我在'Matrix theta = test.times（y）;'这一行得到例外。错误信息几乎就是问题所在。尺寸有问题吗？他们两个都有21个项目，所以我不知道发生了什么。

Answer 1

您犯的错误在以下代码行中：

Matrix inverse = X.times(transposeX).inverse();

您在上面评论的公式是：

//inverse(Tra(X)*X)*tra(X)*y

但你在代码中实际计算的是：（X * Tra（X）代替Tra（X）* X）

//inverse(X*Tra(X))*tra(X)*y

如果X的维数是（m，n），那么

m =行数
n =列数

并且Y的维度为（m，1），使用上面使用的乘法，您将得到以下内容：

逆（X * Tra（X））* Tra（X）* Y =逆* Tra（X）* Y =结果* y

逆（（m，n）（n，m））（n，m）*（m，1）=（m，m）*（n，m）=＆gt;这导致错误，因为矩阵乘法的内部维度必须相等

什么可以修复您的代码将替换以下行：

Matrix inverse = X.times(transposeX).inverse();

与

 Matrix inverse = transposeX.times(X).inverse();

java.lang.IllegalArgumentException：Matrix内部维度必须一致

1 个答案: