Thread: Varying parameters in a cosine fit and calculating chi squared for each set

Hi There. I'm trying to fit a function Acos(wt + theta) to my data that I have binned and need to find the best values for the variable parameters A, w and theta so that the cos function fits to my data. I then evaluate chi squared for my data with this fit to assess the fit. However I've tried making a loop for this but it crashes every time I run it. I'm not sure weather this is because my programme uses a ridiculous amount of memory as I try each combination or I'm doing something wrong with my code? I am pretty new to programming so I haven't done this before so have no idea if there is a more efficient method of doing it?

Code:

#include <stdio.h>
#include<math.h>
#define N_HITS 1800
#define N_TIME_BINS 78
   int main()
     {
     int i, time_bins[N_TIME_BINS],j,k;
	 float event,time_error[N_TIME_BINS];
     float hit[N_HITS],value;
     FILE *fp, *fw, *fy;
     fp = fopen("damadata.txt" , "r");
     fw = fopen("bindata.txt", "w");
	 fy = fopen("chidata.txt", "w");
            
 for (i=0; i<N_HITS ; i++)  /* enter loop to set array elements to zero*/
     {
       hit[i] = 0;
     }
 for (i=0; i<N_TIME_BINS ; i++)
     {
       time_bins[i] = 0;
     }
            
 if (fp != NULL)
     {                                 
        for(i=0; i<N_HITS; i++)                      /*Enter loop to read all lines of data into hit array*/
          {
          fscanf(fp,"%f\n", &event);                 /*Each line is read into a seperate array element*/
          hit[i]=event; 
          }                                 
     for (i = 0; i < N_HITS; i++)                  /*Now cycle through array containing data elements*/
         {                                          /*Open Loop 1*/                          
            for (j = 0; j < N_TIME_BINS; j++)
            {
               value = hit[i];                       /*Value now equal to element i of array*/                     /*enter loop to bin data into 77 bins of group of 60*/
            if (value >= (j*60) && value < ((j+1)*60))    /*Tests if the value lies within a particular boundary*/
                {
                time_bins[j] = (time_bins[j] + 1);                       /*If it is add 1 element into bin j*/
                }                                  
            else
                { 
                time_bins[j] = (time_bins[j]);                       /*If not element j remains the same*/
                }
           }                                             /*Close Loop 1*/
        }                                             /*Close Loop 2*/
    for (j = 0; j <N_TIME_BINS; j++)                       /*Loop to print the number of data points in each bin*/
          {
		  k=time_bins[j];
          time_error[j]=sqrt(k);
          fprintf(fw, "%d\t%d\t%f\n" , (j*60), k, time_error[j]);       /*Prints the bin number and the number of elements in this bin*/
	      }
   }
   else {
         printf("Error: The file you specified could not be found!");
        }
	int theta;
	double w,a,chi_squ_tot,chi_squ_end[10000000],chi,chi_squ,ideal[N_TIME_BINS];
	j=0;
	chi_squ_tot=0;
	for (a=7; a<14; a=a+0.1){                                        /* Varies my 'a' variable through set of sensible values */
		for(w=0.002;w<0.001; w=w+0.005){                             /* Varies my 'w' variable through set of sensible values */
			for(theta=150; theta<250; theta=theta+1){                 /* Varies my 'a' variable through set of sensible values */
               for(i=0; i<N_TIME_BINS; i++){
					ideal[i]=0;                                       
                   ideal[i]=a*cos((w*(i*60))+theta)+11.11;           /*Calcualtes the flux at t given this set of variables*/
				   chi= (time_bins[i]-ideal[i])/time_error[i];       /*Set of setps to calculate chi squared to evaluate fit*/
					chi_squ=chi*chi; 
					chi_squ_tot=chi_squ_tot + chi_squ;

				}
				chi_squ_end[j]=chi_squ_tot;                          /*Passes final value of chi squared to an external variable*/
				j=j+1;
				chi_squ_tot=0;
			}
		}
	}
	for (j=0; j<10000000; j++){
	fprintf(fy, "%d\t%f\n" , j,chi_squ_end[j] );                     /*Prints all values of chi squared so can see which produces best fit*/
		}
   
          fclose(fp);
          fclose(fw);
	      fclose(fy);
     return(0);
}

I've edited the programme to now read

Code:

#include <stdio.h>
#include<math.h>
#define N_HITS 1800
#define N_TIME_BINS 78
   int main()
     {
     int i, time_bins[N_TIME_BINS],j,k;
	 float event,time_error[N_TIME_BINS];
     float hit[N_HITS],value;
     FILE *fp, *fw, *fy;
     fp = fopen("damadata.txt" , "r");
     fw = fopen("bindata.txt", "w");
	 fy = fopen("chidata.txt", "w");
            
 for (i=0; i<N_HITS ; i++)  /* enter loop to set array elements to zero*/
     {
       hit[i] = 0;
     }
 for (i=0; i<N_TIME_BINS ; i++)
     {
       time_bins[i] = 0;
     }
 if (fy == NULL) {
         printf("Error: The file you specified could not be found!");
        } 
 if (fp != NULL)
     {                                 
        for(i=0; i<N_HITS; i++)                      /*Enter loop to read all lines of data into hit array*/
          {
          fscanf(fp,"%f\n", &event);                 /*Each line is read into a seperate array element*/
          hit[i]=event; 
          }                                 
     for (i = 0; i < N_HITS; i++)                  /*Now cycle through array containing data elements*/
         {                                          /*Open Loop 1*/                          
            for (j = 0; j < N_TIME_BINS; j++)
            {
               value = hit[i];                       /*Value now equal to element i of array*/                     /*enter loop to bin data into 77 bins of group of 60*/
            if (value >= (j*60) && value < ((j+1)*60))    /*Tests if the value lies within a particular boundary*/
                {
                time_bins[j] = (time_bins[j] + 1);                       /*If it is add 1 element into bin j*/
                }                                  
            else
                { 
                time_bins[j] = (time_bins[j]);                       /*If not element j remains the same*/
                }
           }                                             /*Close Loop 1*/
        }                                             /*Close Loop 2*/
    for (j = 0; j <N_TIME_BINS; j++)                       /*Loop to print the number of data points in each bin*/
          {
		  k=time_bins[j];
          time_error[j]=sqrt(k);
          fprintf(fw, "%d\t%d\t%f\n" , (j*60), k, time_error[j]);       /*Prints the bin number and the number of elements in this bin*/
	      }
   }
   else {
         printf("Error: The file you specified could not be found!");
        }
	int theta;
	double w,a,chi_squ_tot,chi,chi_squ,ideal;
	j=0;
	chi_squ_tot=0;
	for (a=7; a<14; a=a+0.1){                                        /* Varies my 'a' variable through set of sensible values */
		for(w=0.002;w<0.001; w=w+0.005){                             /* Varies my 'w' variable through set of sensible values */
			for(theta=150; theta<250; theta=theta+1){                 /* Varies my 'a' variable through set of sensible values */
               for(i=0; i<N_TIME_BINS; i++){                                      
                   ideal=a*cos((w*(i*60))+theta)+11.11;           /*Calcualtes the flux at t given this set of variables*/
				   chi= (time_bins[i]-ideal)/time_error[i];       /*Set of setps to calculate chi squared to evaluate fit*/
					chi_squ=chi*chi; 
					chi_squ_tot=chi_squ_tot + chi_squ;

				}
				fprintf(fy, "%f\t%f\t%d\t%f\n" , a, w, theta, chi_squ_tot );
				chi_squ_tot=0;
			}
		}
	}
   
          fclose(fp);
          fclose(fw);
	      fclose(fy);
     return(0);
}

So I've got rid of the huge array, but now I am getting no output written to my chi.txt file when I should be getting the values of a, w, theta and chi squared for each combination and I have no idea why!?!?

Did you even try to debug this yourself before posting? Do your program even reach the line where you write your output to the file?