Problem: Write a Java program to multiply two matrices and output the resultant matrix.
Example:
1 2 3 4 5 6 7 8 9 | m1 = {{1, 2, 3}, {1, 1, 1}} m2 = {{1, 2}, {1, 3}, {1, 1}} m1*m2 = {{6, 11}, {3, 6}} |
Two matrices A and B can only be multiplied, if the number of columns in A is equal to the number of rows in B and the order of the resultant matrix would be (rows of A x columns of B).
Knowing all this, we can multiply two matrix in Java as follows:
- Input
matrix1andmatrix2 - Declare empty resultant matrix of order (r1, c2)
- Loop from 0 to
result.lengthasi:- Nest another loop from 0 to
result[0].lengthasj:- Nest another loop from 0 to
matrix1[0].lengthask:- Sum
(matrix1[I][K] * matrix2[K][J])
- Sum
- Store the sum into the resultant matrix as
result[i][j]=sum
- Nest another loop from 0 to
- End loop.
- Nest another loop from 0 to
- End loop.
- Output the resultant matrix.
Here is the Java program that implements the above logic to multiply two matrices:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 | import java.util.Scanner; class Main { public static void main(String[] args) { Scanner in = new Scanner(System.in); //matrix-I int matrix1[][] = {{1, 2, 3}, {1, 1, 1}}; //matrix-II int matrix2[][] = {{1, 2}, {1, 3}, {1, 1}}; //declare resultant matrix of order (1st.row x 2nd.col) int result[][] = new int[2][2]; //matrix multiplication algorithm for(int i=0; i<result.length; i++){ for(int j=0; j<result[0].length; j++){ int sum=0; for(int k=0; k<matrix1[0].length; k++){ sum += matrix1[i][k]*matrix2[k][j]; } result[i][j] = sum; } } //display the resultant matrix System.out.println("Resultant Matrix"); for(int i=0; i<result.length; i++){ for(int j=0; j<result[0].length; j++){ System.out.print(result[i][j]+ " "); } System.out.println(); } } } |
Output:
Resultant Matrix
6 11
3 6