[Help-gsl] Problems Using the FITSIO Library with a GSL Vector

[Matthew Boulton]

Hello. I am having difficulty using a GSL vector with a function from 
the FITSIO library. I have a test programme below which illustrates this 
problem, with further description given further below:

#include <stdio.h>
#include <fitsio.h>
#include <gsl/gsl_vector.h>

gsl_vector *image;

int main()

{

 fitsfile *data;

 int sub_width = 1536;
 int sub_height = 1536;
 int i;
 char fn[] = "image.fits";

 int status = 0 , anynul;
 int x1 = 1;
 int x2 = sub_width;
 int y1 = 1;
 int y2 = sub_height;
 double nulval = 0.0;
 long fpixel[2] = { x1, y1 };
 long lpixel[2] = { x2, y2 };
 long inc[2] = { 1, 1 };

 image = gsl_vector_calloc( sub_width * sub_height );

 fits_open_file ( &data , fn , READONLY , &status );
 fits_report_error ( stdout , status );

 if ( status != 0 )

 {
  
   printf ( "Cannot Find File: %s\n" , fn );
   exit (0);
  
 }

 status = 0;

 for( i = 0 ; i < sub_width * sub_height ; i+=1000 ) /* Print every 
1000th element */

 {
  
   printf("FITSIO_GSL_test.c: 1: sub_ref[%d] = %g\n" , i , 
gsl_vector_get( image , i ) );

 }

 fits_read_subset( data , TDOUBLE , fpixel , lpixel , inc , &nulval , 
image , &anynul , &status );

 for( i = 0 ; i < sub_width * sub_height ; i+=1000 ) /* Print every 
1000th element */

 {
  
   printf("FITSIO_GSL_test.c: 2: sub_ref[%d] = %g\n" , i , 
gsl_vector_get( image , i ) );

 }

 return 0;

}


Now the image I am testing this on is rather large (9MB) which can be 
found at http://www.dur.ac.uk/m.p.boulton/image.fits .

Sadly I've not been able to quite replicate my original error message 
with the program above, but I'm hoping that fixing the Seg Fault error 
with this program will fix the same problem in my main program. All the 
following applies to my main program.

Basically in my main program I have a GSL vector with all it's elements 
initialised and set to zero. It is then read in by the fits_read_subset 
function. As I have with other functions I assumed I would need to 
change the function declaration to take this change in data type into 
account so after finding that "fits_read_subset" is defined as ffgsv in 
the fitsio.h file I changed:

int ffgsv(fitsfile *fptr, int datatype, long *blc, long *trc, long *inc,
        void *nulval, void *array, int *anynul, int  *status);

to:

int ffgsv(fitsfile *fptr, int datatype, long *blc, long *trc, long *inc,
        void *nulval, gsl_vector *array, int *anynul, int  *status);

where my GSL vector is the 7th argument. I only thought to make this 
change because of the error I was getting. However the change had no 
effect.

Now as soon as I try to read the vector elements with a FOR loop after 
this function has been executed, I get the following error message:

"gsl: vector_source.c:29: ERROR: index out of range"

From what I can tell the FITSIO function is losing my GSL_vector so 
when I come to read any elements (and this applies for any element as 
none can be read) I get the error.

Kind Regards,

Matt