Re: [Help-gsl] Comparing GSL Vector Elements with Double Precision Values

[John Gehman]

Hello Matt,

I didn't think gsl_vectors could be indexed like usual dynamically 
allocated vectors, i.e. by [index]. You need gsl_vector_get( 
gsl_vector, index). But I might have guessed that the errors would have 
more to do with that than the operators. Insofar as your code goes (I 
guess there's nested loops over i and j which aren't shown), all vector 
values are zero by using gsl_vector_calloc. Unless you do some kind of 
conversion of your data into gsl vectors, you'll also want to use 
gsl_vector_set for to set individual elements.

Cheers,
john



On 26/08/2007, at 1:38 AM, Matthew Boulton wrote:

> Hello. I'm having difficult making comparisons between the elements in 
> my GSL vectors and some double precision values in my programmes. I've 
> produced a test programme below which illustrates the problem I am 
> having:
>
> #include <stdio.h>
>
> #include <gsl/gsl_vector.h>
>
> gsl_vector *sub_ref;
> gsl_vector *sub_image;
>
> int main()
>
> {
>
>  int i,j;
>  int sub_width = 1536;
>  int sub_height = 1536;
>  int width = 10000;
>
>  double PIX_MIN = 100.0, SATURATION = 59000.0;
>
>  sub_ref = gsl_vector_calloc( sub_width * sub_height );
>  sub_image = gsl_vector_calloc( sub_width * sub_height );
>
>  if ( sub_image[ i + width * j ] < PIX_MIN || sub_ref[ i + width * j ] 
> < PIX_MIN )
>  {
>      printf("IF 1 executed\n");
>
>  }
>  if (sub_image[ i + width * j ] >= SATURATION || sub_ref[ i + width * 
> j ] >= SATURATION )
>  {
>      printf("IF 2 executed\n");
>
>  }
>
>  return 0;
>
> }
>
> The GSL vectors are being declared as double precision, yet I am 
> getting the following errors:
>
> PIX_MIN_test.c: In function 'main':
> PIX_MIN_test.c:22: error: invalid operands to binary <
> PIX_MIN_test.c:22: error: invalid operands to binary <
> PIX_MIN_test.c:30: error: invalid operands to binary >=
> PIX_MIN_test.c:30: error: invalid operands to binary >=
>
> Can anyone advise me on what I'm doing wrong?
>
> Kind Regards,
>
> Matt
>
> --
> Matthew Boulton
> Level 4 Physics and Astronomy
> Collingwood College
>
> address@hidden
>
>
>
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> Help-gsl mailing list
> address@hidden
> http://lists.gnu.org/mailman/listinfo/help-gsl
---------------------------------------------------------

Dr John Gehman (address@hidden)
Research Fellow; Separovic Lab
School of Chemistry
University of Melbourne (Australia)