Question

我是一个完整的Java新手，我试图将两个2D数组相乘，就像你将两个矩阵相乘一样。以下程序仅适用于方形矩阵，但不适用于其他矩阵。我似乎无法弄清楚我哪里出错了。如果有人可以帮助我，那就太好了。

import java.util.Scanner;

public class TwoDMatrix {
    public static void main (String [] args){
        Scanner scanme = new Scanner(System.in);

        //Input dimensions of Matrix A
        System.out.println("Enter the dimensions (row x column) of Matrix A");
        int rowA = scanme.nextInt();
        int columnA = scanme.nextInt();
        int [][] matA = new int [rowA][columnA];



        //Input dimensions of Matrix B
        System.out.println("Enter the dimensions (row x column) of Matrix B");
        int rowB = scanme.nextInt();
        int columnB = scanme.nextInt();
        int [][] matB = new int [rowB][columnB];



        // Declaring new variables
        int [][] product = new int [columnA][rowB];
        int rowCountA, columnCountA, rowCountB, columnCountB;
        int rowCountProduct, columnCountProduct;
        int sum;
        String divider = "---------";



        // Input values of Matrix A
        for (rowCountA = 0; rowCountA < rowA; rowCountA++){
            for (columnCountA = 0; columnCountA < columnA; columnCountA++){
                System.out.printf("%s%d%s%d%s", "Enter the value at A(", rowCountA, ",", columnCountA, ")");
                matA[rowCountA][columnCountA] = scanme.nextInt();
            }
        }



        // Input values of Matrix B
        for (rowCountB = 0; rowCountB < rowB; rowCountB++){
            for (columnCountB = 0; columnCountB < columnB; columnCountB++){
                System.out.printf("%s%d%s%d%s", "Enter the value at B(", rowCountB, ",", columnCountB, ")");
                matB[rowCountB][columnCountB] = scanme.nextInt();
            }
        }



        //Calculate product of the two matrices
        for (rowCountProduct = 0; rowCountProduct < rowA; rowCountProduct++){
            for (columnCountProduct = 0; columnCountProduct < columnB; columnCountProduct++){
                sum = 0;
                for (columnCountA=0, rowCountB=0; columnCountA<columnA && rowCountB<rowB; columnCountA++, rowCountB++){
                    sum += (matA[rowCountProduct][columnCountA] * matB[rowCountB][columnCountProduct]);
                }
                product[rowCountProduct][columnCountProduct] = sum;
            }
        }



        //Prints the input matrix A
        System.out.printf("%n%s%n%s%n", "Matrix A:", divider);
        for (rowCountA = 0; rowCountA < rowA; rowCountA++){
            for (columnCountA = 0; columnCountA < columnA; columnCountA++){
                System.out.printf("%5d", matA[rowCountA][columnCountA]);
            }
            System.out.println();
        }



        //Prints the input matrix B
        System.out.printf("%n%s%n%s%n", "Matrix B:", divider);
        for (rowCountB = 0; rowCountB< rowB; rowCountB++){
            for (columnCountB = 0; columnCountB < columnB; columnCountB++){
                System.out.printf("%5d", matB[rowCountB][columnCountB]);
            }
            System.out.println();
        }



        //Prints the product
        System.out.printf("%n%s%n%s%n", "Product", divider);
        for (rowCountProduct = 0; rowCountProduct < rowA; rowCountProduct++){
            for (columnCountProduct = 0; columnCountProduct < columnB; columnCountProduct++){
                System.out.printf("%5d", product[rowCountProduct][columnCountProduct]);
            }
            System.out.println();
        }
    }
}

Answer 1

我学习线性代数已经有一段时间了，但我认为当你将矩阵A [n1] [m1]乘以矩阵B [n2] [m2]时，m1必须等于n2，结果应该是是一个矩阵C [n1] [m2]。

因此

int [][] product = new int [columnA][rowB];

应该是

int [][] product = new int [rowA][columnB];

在开始乘法之前，您应该验证columnA == rowB。

Answer 2

你的情况非常复杂：

for (columnCountA=0, rowCountB=0; columnCountA<columnA && rowCountB<rowB; columnCountA++, rowCountB++){
    sum += (matA[rowCountProduct][columnCountA] * matB[rowCountB][columnCountProduct]);
}

记住数学公式：

be A a n x l matrix, B a l x m matrix, then
forall (i,j) in [1,n]x[1,m], (AB)(i,j) = sum_(k in [1,l]) { A(i,k).B(k,j) }

因此，伪代码是：

for (int i=0 ; i<A.length ; i++) {
    for (int j=0 ; j<B[0].length ; j++) {
        prod[i][j] = 0;
        for (int k=0 ; k<A[0].length ; k++) {
            prod[i][j] += A[i][k]*B[k][j];
        }
    }
}

Answer 3

基本上，您将产品矩阵定义为：

    int [][] product = new int [columnA][rowB];

这意味着它应该包含与A中的列一样多的行，以及与B中的行一样多的列。

但是，当你循环填充它时，这就是你的循环：

    for (rowCountProduct = 0; rowCountProduct < rowA; rowCountProduct++){
        for (columnCountProduct = 0; columnCountProduct < columnB; columnCountProduct++){
        ...
        }
    }

这意味着您正在尝试填充产品中的行，这些行应该在0≤rowCountProduct＆lt;范围内。 columnA的值范围为0≤rowCountProduct＆lt; rowA columnB。同样，您可以按照您的定义将列运行到范围rowB而不是{{1}}。

因此，您应该更改矩阵的定义，或者更改填充矩阵的方式。

尝试乘以2d数组（如矩阵乘法），但仅适用于方形矩阵

3 个答案: