使用数组的矩阵乘法

Question

我正在尝试使用多维数组 ( [2][2] ) 制作一个简单的矩阵乘法方法。我对此有点陌生，我只是找不到我做错了什么。如果能告诉我它是什么，我将不胜感激。我宁愿不使用库或类似的东西，我这样做主要是为了了解它是如何工作的。非常感谢你提前。

我在 main 方法中声明我的数组如下：

 Double[][] A={{4.00,3.00},{2.00,1.00}};
Double[][] B={{-0.500,1.500},{1.000,-2.0000}};

A*B 应该返回单位矩阵。它没有。

 public static Double[][] multiplicar(Double[][] A, Double[][] B){
//the method runs and returns a matrix of the correct dimensions
//(I actually changed the .length function to a specific value to eliminate
//it as a possible issue), but not the correct values

    Double[][] C= new Double[2][2];
    int i,j;

    ////I fill the matrix with zeroes, if I don't do this it gives me an error
    for(i=0;i<2;i++) {
        for(j=0;j<2;j++){
            C[i][j]=0.00000;
        }
    }
    ///this is where I'm supposed to perform the adding of every element in
    //a row of A multiplied by the corresponding element in the
    //corresponding column of B, for all columns in B and all rows in A
    for(i=0;i<2;i++){
        for(j=0;j<2;j++)
            C[i][j]+=(A[i][j]*B[j][i]);
    }
    return C;
}

原文由 user2577854 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

你可以试试这段代码：

 public class MyMatrix {
    Double[][] A = { { 4.00, 3.00 }, { 2.00, 1.00 } };
    Double[][] B = { { -0.500, 1.500 }, { 1.000, -2.0000 } };

    public static Double[][] multiplicar(Double[][] A, Double[][] B) {

        int aRows = A.length;
        int aColumns = A[0].length;
        int bRows = B.length;
        int bColumns = B[0].length;

        if (aColumns != bRows) {
            throw new IllegalArgumentException("A:Rows: " + aColumns + " did not match B:Columns " + bRows + ".");
        }

        Double[][] C = new Double[aRows][bColumns];
        for (int i = 0; i < aRows; i++) {
            for (int j = 0; j < bColumns; j++) {
                C[i][j] = 0.00000;
            }
        }

        for (int i = 0; i < aRows; i++) { // aRow
            for (int j = 0; j < bColumns; j++) { // bColumn
                for (int k = 0; k < aColumns; k++) { // aColumn
                    C[i][j] += A[i][k] * B[k][j];
                }
            }
        }

        return C;
    }

    public static void main(String[] args) {

        MyMatrix matrix = new MyMatrix();
        Double[][] result = multiplicar(matrix.A, matrix.B);

        for (int i = 0; i < 2; i++) {
            for (int j = 0; j < 2; j++)
                System.out.print(result[i][j] + " ");
            System.out.println();
        }
    }
}

原文由 amatellanes 发布，翻译遵循 CC BY-SA 3.0 许可协议