#include "cmplx.h"
#define SMALL 0.002


complex Butterworth(w,w1,w2)
float w,w1,w2;
{
complex a;
float real,imag,norm2,w0;
static float a1=3.863703305, a2=7.464101615,a3=9.141620173;

  if(w<SMALL) w=SMALL;
  w0=(w*w-w1*w2)/(w*(w2-w1));
  real=w0*w0*(-a2+a2*w0*w0-w0*w0*w0*w0)+1;
  imag=w0*(a1-a3*w0*w0+a1*w0*w0*w0*w0);
  norm2=real*real+imag*imag;
  a.real=-real/norm2;
  a.imag=+imag/norm2;  /* sign changed by XDL */
  
  return a;

}