Is libgsl a bit broken, or is just me? For example if I try
to compile this simple program :

  #include <math.h>
  #include <gsl_errno.h>
  #include <gsl_fft_real.h>
  #include <gsl_fft_halfcomplex.h>

  void main()
  {
   int i, n = 100;
   double data[n];
   gsl_fft_real_wavetable real_wavetable;

   for (i = 0; i < n; i++)
    data[i] = 0.0;

   for (i = n / 3; i < 2 * n / 3; i++)
    data[i] = 1.0;

   gsl_fft_real_wavetable_alloc( n, &real_wavetable );
   gsl_fft_real_init( n, &real_wavetable );
   gsl_fft_real( data, n, &real_wavetable );
   gsl_fft_real_wavetable_free( &real_wavetable );
 }

using :

  gcc -lgslfft -lgslerr -lm -o fft fft.c

The following errors occur :

  /tmp/cca007241.o: In function `main':
  /tmp/cca007241.o(.text+0x0): multiple definition of `main'
  /usr/lib/libgslfft.a(benchmark.o)(.text+0x0): first
defined here
  ld: Warning: size of symbol `main' changed from 1056 to
481 in /tmp/cca007241.o
  /tmp/cca007241.o: In function `main':
  /tmp/cca007241.o(.text+0x121): undefined reference to
`gsl_fft_real_wavetable_alloc'
  /tmp/cca007241.o(.text+0x134): undefined reference to
`gsl_fft_real_init'
  /tmp/cca007241.o(.text+0x14d): undefined reference to
`gsl_fft_real'
  /tmp/cca007241.o(.text+0x15c): undefined reference to
`gsl_fft_real_wavetable_free'