/* spectrum.c                                   */
/*                                              */
/*       gcc-4.1.0 complilation command:        */
/*                                              */
/*               gcc spectrum.c -lm             */
/*                                              */
/*       g++-4.1.0 compilation command:         */
/*                                              */
/*               g++ spectrum.c                 */
/*                                              */

#include 
#include 
main()
{
   float eta=0.01;
   float x0=4.0;
   int n0=100;

/* there is no complex variable type in c.      */

   float gr, gi;
   float zr, zi;
   float zzr, zzi;

/* open output file.                            */
  
   FILE *fp;
   fp=fopen("output.dat","w");

/* compute frequency increment.                 */

   float x=n0;
   float dx=x0/x;

/* compute number of bins.                      */

   int n=n0*2;

/* loop over frequencies.                       */
  
   float pi=3.1415927;
   int j;
   for(j=0;j0)
      {
         gr=-gr;
         gi=-gi;
      }
      gr=(gr+zzr)/2.0;
      gi=(gi+zzi)/2.0;

/* write result to file.                        */

      fprintf(fp,"%10.4f %10.4f %10.4f\n",x,gr,gi);
      
   }
}