Javascript Program to multiply two matrices

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Given two matrices, the task to multiply them. Matrices can either be square or rectangular.

Examples:

Input : mat1[][] = {{1, 2}, 
                   {3, 4}}
        mat2[][] = {{1, 1}, 
                    {1, 1}}
Output : {{3, 3}, 
          {7, 7}}
Input : mat1[][] = {{2, 4}, 
                    {3, 4}}
        mat2[][] = {{1, 2}, 
                    {1, 3}}       
Output : {{6, 16}, 
          {7, 18}}

Multiplication of Square Matrices :
The below program multiplies two square matrices of size 4*4, we can change N for different dimensions.

Javascript

<script> 
  
// Javascript program to multiply 
// two square matrices. 
  
const N = 4; 
  
// This function multiplies 
// mat1[][] and mat2[][], and 
// stores the result in res[][] 
function multiply(mat1, mat2, res) 
{ 
    let i, j, k; 
    for (i = 0; i < N; i++) { 
        for (j = 0; j < N; j++) { 
            res[i][j] = 0; 
            for (k = 0; k < N; k++) 
                res[i][j] += mat1[i][k] * mat2[k][j]; 
        } 
    } 
} 
  
// Driver Code 
    let i, j; 
      
    // To store result 
    let res = new Array(N); 
    for (let k = 0; k < N; k++) 
        res[k] = new Array(N); 
          
    let mat1 = [ [ 1, 1, 1, 1 ], 
                       [ 2, 2, 2, 2 ], 
                       [ 3, 3, 3, 3 ], 
                       [ 4, 4, 4, 4 ] ]; 
  
    let mat2 = [ [ 1, 1, 1, 1 ], 
                       [ 2, 2, 2, 2 ], 
                       [ 3, 3, 3, 3 ], 
                       [ 4, 4, 4, 4 ] ]; 
  
    multiply(mat1, mat2, res); 
  
    document.write("Result matrix is <br>"); 
    for (i = 0; i < N; i++) { 
        for (j = 0; j < N; j++) 
            document.write(res[i][j] + " "); 
        document.write("<br>"); 
    } 
  
</script>

Output

Result matrix is 
10 10 10 10 
20 20 20 20 
30 30 30 30 
40 40 40 40

Time complexity: O(n³). It can be optimized using Strassen’s Matrix Multiplication

Auxiliary Space: O(n²)

Multiplication of Rectangular Matrices :
We use pointers in C to multiply to matrices. Please refer to the following post as a prerequisite of the code.
How to pass a 2D array as a parameter in C?

Javascript

<script> 
  
// Javascript program to multiply two 
// rectangular matrices 
  
// Multiplies two matrices mat1[][] 
// and mat2[][] and prints result. 
// (m1) x (m2) and (n1) x (n2) are 
// dimensions of given matrices. 
function multiply(m1, m2, mat1, n1, n2, mat2) 
{ 
    let x, i, j; 
    let res = new Array(m1); 
    for (i = 0; i < m1; i++) 
        res[i] = new Array(n2); 
          
    for (i = 0; i < m1; i++)  
    { 
        for (j = 0; j < n2; j++)  
        { 
            res[i][j] = 0; 
            for (x = 0; x < m2; x++)  
            { 
                res[i][j] += mat1[i][x] * mat2[x][j]; 
            } 
        } 
    } 
    for (i = 0; i < m1; i++)  
    { 
        for (j = 0; j < n2; j++)  
        { 
            document.write(res[i][j] + " "); 
        } 
        document.write("<br>"); 
    } 
} 
  
// Driver code 
    let mat1 = [ [ 2, 4 ], [ 3, 4 ] ]; 
    let mat2 = [ [ 1, 2 ], [ 1, 3 ] ]; 
    let m1 = 2, m2 = 2, n1 = 2, n2 = 2; 
    
    // Function call 
    multiply(m1, m2, mat1, n1, n2, mat2); 
      
</script>

Output

6 16 
7 18

Time complexity: O(n³). It can be optimized using Strassen’s Matrix Multiplication

Auxiliary Space: O(m1 * n2)

Please refer complete article on Program to multiply two matrices for more details!

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