double *chebyshev_coef_1d ( int nd, double xd[], double yd[], double &xmin, 
  double &xmax );
double *chebyshev_interp_1d ( int nd, double xd[], double yd[], int ni, 
  double xi[] );
double *chebyshev_value_1d ( int nd, double c[], double xmin, double xmax, 
  int ni, double xi[] );