/* cheb/init.c

 * 

 * Copyright (C) 1996, 1997, 1998, 1999, 2000 Gerard Jungman

 * Copyright (C) 2009 Brian Gough

 * 

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 3 of the License, or (at

 * your option) any later version.

 * 

 * This program is distributed in the hope that it will be useful, but

 * WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * General Public License for more details.

 * 

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.

 */

#include <config.h>

#include <stdlib.h>

#include <gsl/gsl_math.h>

#include <gsl/gsl_errno.h>

#include <gsl/gsl_chebyshev.h>

/*-*-*-*-*-*-*-*-*-*-*-* Allocators *-*-*-*-*-*-*-*-*-*-*-*/

gsl_cheb_series * 

gsl_cheb_alloc(const size_t order)

{

  gsl_cheb_series * cs = (gsl_cheb_series *) malloc(sizeof(gsl_cheb_series));

  if(cs == 0) {

    GSL_ERROR_VAL("failed to allocate gsl_cheb_series struct", GSL_ENOMEM, 0);

  }

  cs->order    = order;

  cs->order_sp = order;

  cs->c = (double *) malloc((order+1) * sizeof(double));

  if(cs->c == 0) {

    GSL_ERROR_VAL("failed to allocate cheb coefficients", GSL_ENOMEM, 0);

  }

  cs->f = (double *) malloc((order+1) * sizeof(double));

  if(cs->f == 0) {

    GSL_ERROR_VAL("failed to allocate cheb function space", GSL_ENOMEM, 0);

  }

  return cs;

}

void gsl_cheb_free(gsl_cheb_series * cs)

{

  RETURN_IF_NULL (cs);

  free(cs->f);

  free(cs->c);

  free(cs);

}

/*-*-*-*-*-*-*-*-*-*-*-* Initializer *-*-*-*-*-*-*-*-*-*-*-*/

int gsl_cheb_init(gsl_cheb_series * cs, const gsl_function *func,

                  const double a, const double b)

{

  size_t k, j;

  if(a >= b) {

    GSL_ERROR_VAL("null function interval [a,b]", GSL_EDOM, 0);

  }

  cs->a = a;

  cs->b = b;

  /* cs->err = 0.0; */

  { 

    double bma = 0.5 * (cs->b - cs->a);

    double bpa = 0.5 * (cs->b + cs->a);

    double fac = 2.0/(cs->order +1.0);

    for(k = 0; k<=cs->order; k++) {

      double y = cos(M_PI * (k+0.5)/(cs->order+1));

      cs->f[k] = GSL_FN_EVAL(func, (y*bma + bpa));

    }

    for(j = 0; j<=cs->order; j++) {

      double sum = 0.0;

      for(k = 0; k<=cs->order; k++) 

        sum += cs->f[k]*cos(M_PI * j*(k+0.5)/(cs->order+1));

      cs->c[j] = fac * sum;

    }

  }

  return GSL_SUCCESS;

}

size_t

gsl_cheb_order (const gsl_cheb_series * cs)

{

  return cs->order;

}

size_t

gsl_cheb_size (const gsl_cheb_series * cs)

{

  return (cs->order + 1);

}

double *

gsl_cheb_coeffs (const gsl_cheb_series * cs)

{

  return cs->c;

}