/* calculate Chebyshev polynomials */

#include <math.h>
#include "../iolib/message.h"

float Chebyshev(n,x,ifnorm)
int n,ifnorm;
float x;
{
double a,dbln;
float f;

      if(x<-1.0 || x>1.0 || n<0) STOP(Chebyshev: wrong argument);
      dbln=(double)n;
      a=acos((double)x)*dbln;
      f=cos(a);
      if(ifnorm)
      { dbln=4.*dbln*dbln;
        if(n) f*=sqrt((dbln-1.)/(dbln-2.));
        else f*=sqrt(2.);
      }
      return(f);
}