/**************************************************
* Chebyshev Approximation of a user defined real  *
* function FUNC(X) in double precision.           *
* ----------------------------------------------- *
* SAMPLE RUN:                                     *
* (Approximate sin(x) from x=0 to x=PI).          *
*                                                 *
* Chebyshev coefficients (N=10):                  *
*  0.94400243153647                               *
*  0.00000000000000                               *
* -0.49940325827041                               *
* -0.00000000000000                               *
*  0.02799207961755                               *
* -0.00000000000000                               *
* -0.00059669519580                               *
*  0.00000000000000                               *
*  0.00000670417552                               *
* -0.00000000000000                               *
*      X          Chebyshev Eval.     SIN(X)      *
*  -------------------------------------------    *
*  0.00000000       0.00000005      0.00000000    *
*  0.34906585       0.34202018      0.34202014    *
*  0.69813170       0.64278757      0.64278761    *
*  1.04719755       0.86602545      0.86602540    *
*  1.39626340       0.98480773      0.98480775    *
*  1.74532925       0.98480773      0.98480775    *
*  2.09439510       0.86602545      0.86602540    *
*  2.44346095       0.64278757      0.64278761    *
*  2.79252680       0.34202018      0.34202014    *
*  3.14159265       0.00000005      0.00000000    *
*                                                 *
*               C++ Release By J-P Moreau, Paris. *
*                      (www.jpmoreau.fr)          *
**************************************************/
// To link with Chebyshe.cpp
#include <stdio.h>
#include <math.h>

#define  NMAX  51
#define  HALF  0.5
#define  TWO   2.0
#define  ZERO  0.0
#define  PI    4.0*atan(1.0)


    void   CHEBFT(double A,double B, double *C, int N);
    double CHEBEV(double A,double B, double *C, int M, double X);
    
    double X0,X1, COEFF[NMAX];
    double DX, X;
    int I, N;

    // user defined function
    double FUNC(double x) {
      return (sin(x));
    }

void main() {

  N=10;
  X0=ZERO; X1=PI;

  CHEBFT(X0,X1,COEFF,N);

  printf(" Chebyshev coefficients (N=%d):\n", N);
  for (I=1; I<=N; I++)
    printf(" %17.14f\n", COEFF[I]);

  DX=(X1-X0)/(N-1);
  X=X0-DX;

  printf("      X        Chebyshev Eval.     SIN(X)    \n");
  printf(" --------------------------------------------\n");
  for (I=1; I<=N; I++) {
    X += DX;
    printf("%11.8f %15.8f %15.8f\n", X, CHEBEV(X0,X1,COEFF,N,X), FUNC(X));
  }

}

// end of file Tchebysh.cpp