#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#define Grid_size 100
#define Header_size 4100

main()
{
int i,j;
double x;
int fd;
double data[Grid_size];
char information[Header_size];
FILE *sortie;
double ui,uj;

sortie = fopen("test2.dat","w");          /* open the test2.dat for writing operations*/

sprintf(information,"Some useful info like date, array size,..."); 
fwrite(information,sizeof(char),Header_size,sortie);           /* here we put some arbitrary info in the first 4100 bytes of our binary file */

for(i=0;i<Grid_size;i++)
	{
	ui = (double)(i-Grid_size/2)/Grid_size;	
       	for(j=0;j<Grid_size;j++)
		{
		uj = (double)(j-Grid_size/2)/Grid_size;	
		data[j] = sin( 6*M_PI*(ui*ui + uj*uj) ) ;
		}
	fwrite(data,sizeof(double),Grid_size,sortie);
	}
fclose(sortie);
}