[Help-gsl] How to use 'gsl_blas_dnrm2'?

[Lukas Gradl]

Hello,

I am new to the GSL and C and I am having some trouble using the
function gsl_blas_dnrm2.  I have the following example program:


---8<--- cut here -------------------- start --->8---
#include <stdio.h>
#include <gsl/gsl_vector.h>
#include <gsl/gsl_cblas.h>

int main ()
{
  gsl_vector *a = gsl_vector_alloc(3);
  gsl_vector_set_all(a, 0.50);

  double nrm;
  nrm = gsl_blas_dnrm2(a);

  fprintf(stdout, "%f\n", nrm);

  gsl_vector_free(a);
  return 0;
}
---8<--- cut here -------------------- end ----->8---


The output that I expect from this program is 0.8660254.
However, if I compile and run the program I get the following:


---8<--- cut here -------------------- start --->8---
address@hidden gcc -lgsl -lcblas -latlas -lm test.c
test.c: In function ‘main’:
test.c:11:9: warning: implicit declaration of function ‘gsl_blas_dnrm2’ 
[-Wimplicit-function-declaration]
   nrm = gsl_blas_dnrm2(a);
         ^~~~~~~~~~~~~~
address@hidden ./a.out
24666208.000000
address@hidden ./a.out
45424736.000000
---8<--- cut here -------------------- end ----->8---


The output is actually different every time I run the program without
recompiling.

I tried to do the same using the CBLAS library that comes with GSL
instead of Atlas.  In that case the output is always the number 3.0:


---8<--- cut here -------------------- start --->8---
address@hidden gcc -lgsl -lgslcblas -lm test.c
test.c: In function ‘main’:
test.c:11:9: warning: implicit declaration of function ‘gsl_blas_dnrm2’ 
[-Wimplicit-function-declaration]
   nrm = gsl_blas_dnrm2(a);
         ^~~~~~~~~~~~~~
address@hidden ./a.out
3.000000
address@hidden ./a.out
3.000000
---8<--- cut here -------------------- end ----->8---


How would I use this function so that it gives the correct result?  My
guess is that I am making a trivial mistake somewhere but I can't find
it.

Thank you for your help!

Best,
Lukas

signature.asc
Description: PGP signature