Matrix Multiplication Program in Java

Matrix Multiplication Program :

To multiply two matrices we need to first check whether the two matrices can be multiplied or not. For that compare the first matrix column with the rows of second matrix, if they are equal than only the two matrices can be multiplied with each other.

For example :

Let the first matrix be of the order 3X3 and second matrix be of the order of 3X2. Since both the no. of columns in first matrix and no. of rows in second matrix are equal i.e. 3, the two matrices can be multiplied with each other and the resultant matrix will be of the order 3X2 (rows in first matrix and columns in second matrix).

In general,

M(ixj) * M(jxk) = M(ixk)

To multiply the two matrices we need to multiply the rows of first matrix to the columns of second matrix as shown below in the diagram.

Now let’s consider the program of matrix multiplication in which the two matrices are multiplied with the use of three nested loops.

 import java.util.Scanner;  
   
 class MatrixMulDemo  
 {  
      public static void main(String[] args)  
      {  
           //make a scanner for rows and columns  
           Scanner scan = new Scanner(System.in);  
   
           System.out.println("Enter the number of rows for first matrix");  
   
           //store rows in a variable  
           int rowsFirst = scan.nextInt();  
           System.out.println("Enter the number of columns for first matrix / rows of   
   
 second matrix (they must be same for matrix multiplication");  
             
           //store columns in a variable  
           int colFirstRowSec = scan.nextInt();  
   
           System.out.println("Enter the columns for second matrix");  
           //store columns of second matrix in a variable  
           int colSec = scan.nextInt();  
   
           //make two dimensional arrays for storing the matrices elements  
   
           int[][] first = new int[rowsFirst][colFirstRowSec];  
           int[][] second = new int[colFirstRowSec][colSec];  
   
           System.out.println("Enter the values of first matrix");  
           for(int i=0; i<first.length; i++)  
           {  
                for(int j=0; j<first[0].length; j++)  
                {  
                     first[i][j] = scan.nextInt();  
                }  
           }  
   
           System.out.println("Enter the values of second matrix");  
           for(int i=0; i<second.length; i++)  
           {  
                for(int j=0; j<second[0].length; j++)  
                {  
                     second[i][j] = scan.nextInt();  
                }  
           }  
   
           //define the third resultant matrix  
           int result[][] = new int[rowsFirst][colSec];  
   
           //multiply the two matrices using three nested loops  
           for(int i=0; i<rowsFirst; i++)  
           {  
                for(int j=0; j<colSec; j++)  
                {  
                     for(int k=0; k<colFirstRowSec; k++)  
                     {  
                          result[i][j] = result[i][j] + first[i][k] * second  
   
 [k][j];  
                     }  
                }  
           }  
   
           //print all the elements of result matrix  
           System.out.println("Product of two matrices ");  
           for(int i=0; i<result.length; i++)  
           {  
                for(int j=0; j<result[0].length; j++)  
                {  
                     System.out.print(result[i][j] + " ");  
                }  
                //for line gap  
                System.out.println();  
           }  
      }  
 }  

Output :