double *lagcheby1_interp_1d ( int nd, double xd[], double yd[], int ni, 
  double xi[] );
double *lagcheby2_interp_1d ( int nd, double xd[], double yd[], int ni, 
  double xi[] );
double *lageven_interp_1d ( int nd, double xd[], double yd[], int ni, 
  double xi[] );