Re: [Help-gsl] what's wrong in my poly code?

[Colin Torney]

On Fri, 2006-11-10 at 20:55 +0100, Marco Maggi wrote:
> If I run the following GNU Octave code:
> 
> real_coeffs = [1 2 3 4 5];
> roots(real_coeffs)
> 
> I get:
> 
> ans =
> 
>      -1.2878 +     0.8579i
>      -1.2878 -     0.8579i
>      0.28782 +     1.4161i
>      0.28782 -     1.4161i
> 
> if I run the following GSL code:
> 
> #include <gsl/gsl_poly.h>
> #include <stdio.h>
> #include <stdlib.h>
> 
> 
> int
> main (int argc, const char *const argv[])
> {
>   gsl_poly_complex_workspace *        w;
>   double      coeffs[5] = { 1.0, 2.0, 3.0, 4.0, 5.0 };
>   double      result[10];
>   int         e;
>   size_t      i;
> 
> 
>   w = gsl_poly_complex_workspace_alloc(5);
>   e = gsl_poly_complex_solve(coeffs, 5, w, result);
>   gsl_poly_complex_workspace_free(w);
> 
>   for (i=0; i<8; i+=2)
>     {
>       printf("%f %f\n", result[i], result[i+1]);
>     }
>   return 0;
> }
> 
> I get:
> 
> 0.137832 0.678154
> 0.137832 -0.678154
> -0.537832 0.358285
> -0.537832 -0.358285
> 
> what am I doing wrong?
> 
> TIA
> 
> --
> Marco Maggi
> 
> "They say jump!, you say how high?"
> Rage Against the Machine - "Bullet in the Head"
> 
> 
> 
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Marco
It's just in wrong order

octave:3> co=[5 4 3 2 1];
octave:4> roots(co)
ans =

   0.13783 +  0.67815i
   0.13783 -  0.67815i
  -0.53783 +  0.35828i
  -0.53783 -  0.35828i

Colin