#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define NPERIOD    50		/* maximum number of period values */
#define NPHASE     20		/* maximum number of phase  values */

struct dpoint {			/* define set of period, phase, and chi2 */
	double period;
	double phase;
	double chi2;
};

void FGS01(struct dpoint *spointset);

void FGS02(struct dpoint *spointset, int n, double *sumval);

int main()  {
		FILE *fp;
		char *FGS01f = "fgs01_snippet.dat";	/* contains output data */

		int i,j,k;
		double pi, sumval;
		struct dpoint pointset[NPERIOD*NPHASE];

		pi = 2*asin(1.0);

		/* Write out parameters to file */
		if ((fp = fopen(FGS01f,"w")) == NULL)  {
		  printf("Could not open file for writing: %s - ",FGS01f);
		  abort();
		}
		fprintf(fp,"# \n# FGS Sample Parameters (period, phase, and chi2) \n# \n");

		/* Calculate chi2 values by passing structure to function */
		for (i = 0; i < NPERIOD; i++)  {
			for (j = 0; j < NPHASE; j++)  {

				k = i*NPHASE + j;
				pointset[k].period = i;
				pointset[k].phase  = (2*pi) * (double)j / (double)NPHASE;

				FGS01(&pointset[k]);

				fprintf(fp,"%4d %4d %8d %10.4f %10.4f %10.4f \n", 
				i, j, k, pointset[k].period, pointset[k].phase, pointset[k].chi2);
			}
		}

		/* Calculate summed function by accessing entire array of structures within function */
		FGS02(&pointset[0], NPERIOD*NPHASE, &sumval);
		fprintf(fp,"# \n%12.4f\n# \n", sumval);

		fclose(fp);
		
		return 0;
}

/* FGS01: function to show array of structures input into a function */
void FGS01(struct dpoint *spointset)
{	
	/* Fill chi2 values based on period and phase values */
	spointset->chi2 = spointset->period * spointset->phase;
	
	return;
}

/* FGS02: function to show array of structures input into a function */
void FGS02(struct dpoint *spointset, int n, double *sumval)
{	
	int i;

	/* Calculate sum of the square of the chi-squared component of the structure */
	*sumval = 0.0;
	for (i = 0; i < n; i++)  {
		*sumval += spointset->chi2 * spointset->chi2;
		spointset++;
	}
	
	return;
}