How to Code Matrix Multiplication in Java?

Matrix multiplication is a fundamental operation in linear algebra and is widely used in various applications, including computer graphics, machine learning, and data analysis. In this article, we will explore how to perform matrix multiplication in Java using nested loops. We will also discuss the conditions required for matrix multiplication to be valid and provide a complete code example.

Understanding Matrix Multiplication

Matrix multiplication involves multiplying two matrices to produce a third matrix. The number of columns in the first matrix must equal the number of rows in the second matrix for multiplication to be possible. If matrix A has dimensions m×n and matrix B has dimensions n×p, the resulting matrix C will have dimensions m×p.

Rule of the Matrix Multiplication

Two matrices can be multiplied only if the number of columns in the first matrix matches the number of rows in the second matrix.

Visual Representation of Matric Multiplication

Matrix Multiplication Code Example in Java

Here’s a complete Java program that demonstrates how to perform matrix multiplication:

import java.util.Scanner;

public class MatrixMultiplication {

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

        // Input dimensions for first matrix
        System.out.print("Enter number of rows for first matrix: ");
        int rowsA = scanner.nextInt();
        System.out.print("Enter number of columns for first matrix: ");
        int colsA = scanner.nextInt();

        // Input dimensions for second matrix
        System.out.print("Enter number of rows for second matrix: ");
        int rowsB = scanner.nextInt();
        System.out.print("Enter number of columns for second matrix: ");
        int colsB = scanner.nextInt();

        // Check if multiplication is possible
        if (colsA != rowsB) {
            System.out.println("Matrix multiplication not possible.");
            return;
        }

        // Initialize matrices
        int[][] A = new int[rowsA][colsA];
        int[][] B = new int[rowsB][colsB];
        int[][] C = new int[rowsA][colsB];

        // Input elements for first matrix
        System.out.println("Enter elements of first matrix:");
        for (int i = 0; i < rowsA; i++) {
            for (int j = 0; j < colsA; j++) {
                A[i][j] = scanner.nextInt();
            }
        }

        // Input elements for second matrix
        System.out.println("Enter elements of second matrix:");
        for (int i = 0; i < rowsB; i++) {
            for (int j = 0; j < colsB; j++) {
                B[i][j] = scanner.nextInt();
            }
        }

        // Perform matrix multiplication
        for (int i = 0; i < rowsA; i++) {
            for (int j = 0; j < colsB; j++) {
                C[i][j] = 0; // Initialize result cell
                for (int k = 0; k < colsA; k++) {
                    C[i][j] += A[i][k] * B[k][j];
                }
            }
        }

        // Output result
        System.out.println("Resultant Matrix:");
        printMatrix(C);
    }

    // Method to print a matrix
    public static void printMatrix(int[][] matrix) {
        for (int[] row : matrix) {
            for (int value : row) {
                System.out.print(value + " ");
            }
            System.out.println();
        }
    }
}

Explanation of the Code

• Input Dimensions: The program begins by prompting the user to enter the dimensions of both matrices. It checks if multiplication is possible by comparing the number of columns in the first matrix with the number of rows in the second.
• Matrix Initialization: It initializes three matrices: A, B, and C (the result).
• Input Elements: The user is prompted to enter the elements of both matrices.
• Matrix Multiplication Logic:
  Nested loops are used to iterate through each element of the resulting matrix.
  The innermost loop calculates the dot product by summing up the products of corresponding elements from row i of A and column j of B.
• Printing Result: Finally, it prints the resultant matrix using a helper method printMatrix.

Example Output

When you run this program, you might see output similar to this:

Conclusion

Matrix multiplication is an essential operation in many fields, including computer science and engineering. This Java program provides a straightforward approach to performing this operation using nested loops. By understanding how to implement this functionality, beginners can strengthen their programming skills while gaining insight into mathematical operations in programming.