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Kronecker Product of two matrices

Given a  {m}	imes{n} matrix A and a  {p}	imes{q} matrix B, their Kronecker product C = A tensor B, also called their matrix direct product, is an  {(mp)}	imes{(nq)} matrix.

A tensor B =  |a11B   a12B|
              |a21B   a22B|

= |a11b11   a11b12   a12b11  a12b12|
  |a11b21   a11b22   a12b21  a12b22| 
  |a11b31   a11b32   a12b31  a12b32|
  |a21b11   a21b12   a22b11  a22b12|
  |a21b21   a21b22   a22b21  a22b22|
  |a21b31   a21b32   a22b31  a22b32|

Examples :

1. The matrix direct(kronecker) product of the 2×2 matrix A 
   and the 2×2 matrix B is given by the 4×4 matrix :

Input : A = 1 2    B = 0 5
            3 4        6 7

Output : C = 0  5  0  10
             6  7  12 14
             0  15 0  20
             18 21 24 28

2. The matrix direct(kronecker) product of the 2×3 matrix A 
   and the 3×2 matrix B is given by the 6×6 matrix :

Input : A = 1 2    B = 0 5 2
            3 4        6 7 3
            1 0

Output : C = 0      5    2    0     10    4    
             6      7    3   12     14    6    
             0     15    6    0     20    8    
            18     21    9   24     28   12    
             0      5    2    0      0    0    
             6      7    3    0      0    0    

Below is the code to find the Kronecker Product of two matrices and stores it as matrix C :

C

// C code to find the Kronecker Product of two
// matrices and stores it as matrix C
#include <stdio.h>
  
// rowa and cola are no of rows and columns
// of matrix A
// rowb and colb are no of rows and columns
// of matrix B
const int cola = 2, rowa = 3, colb = 3, rowb = 2;
  
// Function to computes the Kronecker Product
// of two matrices
void Kroneckerproduct(int A[][cola], int B[][colb])
{
  
    int C[rowa * rowb][cola * colb];
  
    // i loops till rowa
    for (int i = 0; i < rowa; i++) {
  
        // k loops till rowb
        for (int k = 0; k < rowb; k++) {
  
            // j loops till cola
            for (int j = 0; j < cola; j++) {
  
                // l loops till colb
                for (int l = 0; l < colb; l++) {
  
                    // Each element of matrix A is
                    // multiplied by whole Matrix B
                    // resp and stored as Matrix C
                    C[i + l + 1][j + k + 1] = A[i][j] * B[k][l];
                    printf("%d ", C[i + l + 1][j + k + 1]);
                }
            }
            printf(" ");
        }
    }
}
  
// Driver Code
int main()
{
    int A[3][2] = { { 1, 2 }, { 3, 4 }, { 1, 0 } },
        B[2][3] = { { 0, 5, 2 }, { 6, 7, 3 } };
  
    Kroneckerproduct(A, B);
    return 0;
}

Java

// Java code to find the Kronecker Product of
// two matrices and stores it as matrix C
import java.io.*;
import java.util.*;
  
class GFG {
          
    // rowa and cola are no of rows and columns
    // of matrix A
    // rowb and colb are no of rows and columns
    // of matrix B
    static int cola = 2, rowa = 3, colb = 3, rowb = 2;
      
    // Function to computes the Kronecker Product
    // of two matrices
    static void Kroneckerproduct(int A[][], int B[][])
    {
      
        int[][] C= new int[rowa * rowb][cola * colb];
      
        // i loops till rowa
        for (int i = 0; i < rowa; i++) 
        {
      
            // k loops till rowb
            for (int k = 0; k < rowb; k++)
            {
      
                // j loops till cola
                for (int j = 0; j < cola; j++) 
                {
      
                    // l loops till colb
                    for (int l = 0; l < colb; l++)
                    {
      
                        // Each element of matrix A is
                        // multiplied by whole Matrix B
                        // resp and stored as Matrix C
                        C[i + l + 1][j + k + 1] = A[i][j] * B[k][l];
                        System.out.print( C[i + l + 1][j + k + 1]+" ");
                    }
                }
                System.out.println();
            }
        }
    }
      
    // Diver program
    public static void main (String[] args)
    {
        int A[][] = { { 1, 2 },
                      { 3, 4 }, 
                      { 1, 0 } };
                        
        int B[][] = { { 0, 5, 2 },
                      { 6, 7, 3 } };
      
        Kroneckerproduct(A, B); 
    }
}
  
// This code is contributed by Gitanjali.

Python3

# Python3 code to find the Kronecker Product of two
# matrices and stores it as matrix C
   
# rowa and cola are no of rows and columns
# of matrix A
# rowb and colb are no of rows and columns
# of matrix B
cola = 2
rowa = 3
colb = 3
rowb = 2
   
# Function to computes the Kronecker Product
# of two matrices
  
def Kroneckerproduct( A , B ):
      
    C = [[0 for j in range(cola * colb)] for i in range(rowa * rowb)]
   
    # i loops till rowa
    for i in range(0, rowa):
          
        # k loops till rowb
        for k in range(0, rowb):
   
            # j loops till cola
            for j in range(0, cola):
   
                # l loops till colb
                for l in range(0, colb):
   
                    # Each element of matrix A is
                    # multiplied by whole Matrix B
                    # resp and stored as Matrix C
                    C[i + l + 1][j + k + 1] = A[i][j] * B[k][l]
                    print (C[i + l + 1][j + k + 1],end=' ')
              
              
            print (" ")
          
  
# Driver code.
  
A = [[0 for j in range(2)] for i in range(3)]
B = [[0 for j in range(3)] for i in range(2)]
  
A[0][0] = 1
A[0][1] = 2
A[1][0] = 3
A[1][1] = 4
A[2][0] = 1
A[2][1] = 0
  
B[0][0] = 0
B[0][1] = 5
B[0][2] = 2
B[1][0] = 6
B[1][1] = 7
B[1][2] = 3
  
Kroneckerproduct( A , B )
  
# This code is contributed by Saloni.

C#

// C# code to find the Kronecker Product of
// two matrices and stores it as matrix C
using System;
  
class GFG {
          
    // rowa and cola are no of rows 
    // and columns of matrix A
    // rowb and colb are no of rows
    //  and columns of matrix B
    static int cola = 2, rowa = 3;
    static int colb = 3, rowb = 2;
      
    // Function to computes the Kronecker 
    // Product of two matrices
    static void Kroneckerproduct(int [,]A, int [,]B)
    {
      
        int [,]C= new int[rowa * rowb, 
                          cola * colb];
      
        // i loops till rowa
        for (int i = 0; i < rowa; i++) 
        {
      
            // k loops till rowb
            for (int k = 0; k < rowb; k++)
            {
      
                // j loops till cola
                for (int j = 0; j < cola; j++) 
                {
      
                    // l loops till colb
                    for (int l = 0; l < colb; l++)
                    {
      
                        // Each element of matrix A is
                        // multiplied by whole Matrix B
                        // resp and stored as Matrix C
                        C[i + l + 1, j + k + 1] = A[i, j] * 
                                                  B[k, l];
                        Console.Write( C[i + l + 1, 
                                       j + k + 1] + " ");
                    }
                }
                Console.WriteLine();
            }
        }
    }
      
    // Diver Code
    public static void Main ()
    {
        int [,]A = {{1, 2},
                   {3, 4}, 
                   {1, 0}};
                          
        int [,]B = {{0, 5, 2},
                   {6, 7, 3}};
      
        Kroneckerproduct(A, B); 
    }
}
  
// This code is contributed by nitin mittal.

PHP

<?php
// PHP code to find the
// Kronecker Product of two
  
// rowa and cola are no of 
// rows and columns of matrix A
// rowb and colb are no of 
// rows and columns of matrix B
$cola = 2;
$rowa = 3;
$colb = 3;
$rowb = 2;
  
// Function to computes the 
// Kronecker Product of two matrices
function Kroneckerproduct($A, $B)
{
    global $cola;
    global $rowa;
    global $colb;
    global $rowb;
  
  
    //$C[$rowa * $rowb][$cola * $colb];
    $C;
  
    // i loops till rowa
    for ( $i = 0; $i < $rowa; $i++)
    {
  
        // k loops till rowb
        for ($k = 0; $k < $rowb; $k++) 
        {
  
            // j loops till cola
            for ( $j = 0; $j < $cola; $j++)  
            {
  
                // l loops till colb
                for ($l = 0; $l < $colb; $l++) 
                {
  
                    // Each element of matrix A is
                    // multiplied by whole Matrix B
                    // resp and stored as Matrix C
                    $C[$i + $l + 1][$j + $k + 1] = $A[$i][$j] * 
                                                   $B[$k][$l];
                    echo ($C[$i + $l + 1][$j + $k + 1]), " " ;
                }
            }
        echo " ";
        }
    }
}
  
// Driver Code
$A = array (array (1, 2), 
            array (3, 4), 
            array (1, 0));
$B = array (array (0, 5, 2),
            array (6, 7, 3));
  
Kroneckerproduct($A, $B);
  
// This code is contributed by ajit
?>

Output :

0    5    2    0    10    4    
6    7    3    12   14    6    
0    15   6    0    20    8    
18   21   9    24   28    12    
0    5    2    0    0     0    
6    7    3    0    0     0


This article is attributed to GeeksforGeeks.org

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