#ifndef main1
    #include <stdio.h>
    #include <stdlib.h>
    #define mat_mul__main 1
    #define mat_mul__out 1
#endif


double *mat_mul(double A[],double B[],int I,int K,int J)
{
    int i,j,k;double *mat_mul_return;

    mat_mul_return=calloc( I*J , sizeof(double) );

    for(i=0;i<I;i++)
        for(j=0;j<J;j++)
            for(k=0;k<K;k++)
                mat_mul_return[i*J+j] += A[i*K+k]*B[k*J+j];

    #if mat_mul__out
        for(i=0;i<I;i++)
            for(j=0;j<J;j++)
                {
                    printf("%12g",mat_mul_return[i*J+j]);
                    if(j==J-1)
                        printf("\n");
                }
    #endif

    return mat_mul_return;
}

#ifdef mat_mul__main
    int main()
        {
            double A[]={1,2,3,4},B[]={1,2,3,4},*p;

            p=mat_mul(A,B,2,2,2);

            return 0;
        }
#endif

#include <stdio.h>
#include <stdlib.h>
#define main1
#define mat_mul__out 1
#include "matrix.c"

int main()
{
    double A[]={9,2,3,8},B[]={1,2,3,4},*p;
    p=mat_mul(A,B,2,2,2);
}