Task: Kronecker product
C: #include<stdlib.h>
#include<stdio.h>

int main(){
	
	char input[100],output[100];
	int i,j,k,l,rowA,colA,rowB,colB,rowC,colC,startRow,startCol;
	double **matrixA,**matrixB,**matrixC;
	
	printf("Enter full path of input file : ");
	fscanf(stdin,"%s",input);
	
	printf("Enter full path of output file : ");
	fscanf(stdin,"%s",output);
	
	FILE* inputFile = fopen(input,"r");
	
	fscanf(inputFile,"%d%d",&rowA,&colA);
	
	matrixA = (double**)malloc(rowA * sizeof(double*));
	
	for(i=0;i<rowA;i++){
		matrixA[i] = (double*)malloc(colA*sizeof(double));
		for(j=0;j<colA;j++){
			fscanf(inputFile,"%lf",&matrixA[i][j]);
		}
	}
	
	fscanf(inputFile,"%d%d",&rowB,&colB);
	
	matrixB = (double**)malloc(rowB * sizeof(double*));
	
	for(i=0;i<rowB;i++){
		matrixB[i] = (double*)malloc(colB*sizeof(double));
		for(j=0;j<colB;j++){
			fscanf(inputFile,"%lf",&matrixB[i][j]);
		}
	}
	
	fclose(inputFile);
	
	rowC = rowA*rowB;
	colC = colA*colB;
	
	matrixC = (double**)malloc(rowC*sizeof(double*));
	
	for(i=0;i<rowA*rowB;i++){
		matrixC[i] = (double*)malloc(colA*colB*sizeof(double));
	}
	
	for(i=0;i<rowA;i++){
		for(j=0;j<colA;j++){
			startRow = i*rowB;
			startCol = j*colB;
			for(k=0;k<rowB;k++){
				for(l=0;l<colB;l++){
					matrixC[startRow+k][startCol+l] = matrixA[i][j]*matrixB[k][l];
				}
			}
		}
	}

	FILE* outputFile = fopen(output,"w");
	
	for(i=0;i<rowC;i++){
		for(j=0;j<colC;j++){
			fprintf(outputFile,"%lf\t",matrixC[i][j]);
		}
		fprintf(outputFile,"\n");
	}
	
	fclose(outputFile);
	
	printf("\n\n\nKronecker product of the two matrices written to %s.",output);
}

Java: package kronecker;


public class Product {
  
  public static int[][] product(final int[][] a, final int[][] b) {
    
    
    final int[][] c = new int[a.length*b.length][];
    
    
    for (int ix = 0; ix < c.length; ix++) {
      final int num_cols = a[0].length*b[0].length;
      c[ix] = new int[num_cols];
    }
    
    
    for (int ia = 0; ia < a.length; ia++) {
      for (int ja = 0; ja < a[ia].length; ja++) {
        
        for (int ib = 0; ib < b.length; ib++) {
          for (int jb = 0; jb < b[ib].length; jb++) {
             c[b.length*ia+ib][b[ib].length*ja+jb] = a[ia][ja] * b[ib][jb];
          }
        }
      }
    }

    
    return c;
  }

  
  public static void print_matrix(final int[][] m) {
    
    
    
    
    final String[][] sts = new String[m.length][];
    int max_length = 0;  
    for (int im = 0; im < m.length; im++) {
      sts[im] = new String[m[im].length];
      for (int jm = 0; jm < m[im].length; jm++) {
        final String st = String.valueOf(m[im][jm]);
        if (st.length() > max_length) {
          max_length = st.length();
        }
        sts[im][jm] = st;
      }
    }

    
    
    
    final String format = String.format("%%%ds", max_length);
    for (int im = 0; im < m.length; im++) {
      System.out.print("|");
      
      for (int jm = 0; jm < m[im].length - 1; jm++) {
        System.out.format(format, m[im][jm]);
        System.out.print(" ");
      }
      System.out.format(format, m[im][m[im].length - 1]);
      System.out.println("|");
    }
  }

  
  private static void test(final int[][] a, final int[][] b) {
    
    System.out.println("Testing Kronecker product");
    System.out.println("Size of matrix a: " + a.length + " by " + a[0].length);
    System.out.println("Matrix a:");
    print_matrix(a);
    System.out.println("Size of matrix b: " + b.length + " by " + b[0].length);
    System.out.println("Matrix b:");
    print_matrix(b);
    System.out.println("Calculating matrix c as Kronecker product");
    final int[][] c = product(a, b);
    System.out.println("Size of matrix c: " + c.length + " by " + c[0].length);
    System.out.println("Matrix c:");
    print_matrix(c);
  }

  
  private static void test1() {
    
    final int[][] a = new int[2][];  
    a[0] = new int[]{1, 2};
    a[1] = new int[]{3, 4};
    final int[][] b = new int[2][];  
    b[0] = new int[]{0, 5};
    b[1] = new int[]{6, 7};
    
    test(a, b);
  }

  
  private static void test2() {
    
    final int[][] a = new int[3][];  
    a[0] = new int[]{0, 1, 0};
    a[1] = new int[]{1, 1, 1};
    a[2] = new int[]{0, 1, 0};
    final int[][] b = new int[3][];  
    b[0] = new int[]{1, 1, 1, 1};
    b[1] = new int[]{1, 0, 0, 1};
    b[2] = new int[]{1, 1, 1, 1};
    
    test(a, b);
  }

  
  public static void main(final String[] args) {
    
    test1();
    test2();
  }

}