java - 尝试乘以二维数组(如矩阵乘法)，但仅适用于方阵

Question

我是一个完全的 Java 新手，我试图将两个 2D 数组相乘，就像将两个矩阵相乘一样。下面的程序仅适用于方阵，不适用于其他矩阵。我似乎无法弄清楚我哪里出了问题。如果有人能帮助我，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。