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/* interpolation/linear.c
*
* Copyright (C) 1996, 1997, 1998, 1999, 2000 Gerard Jungman
*
* 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 2 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.
*/
/* Author: G. Jungman
*/
#include <config.h>
#include <stdlib.h>
#include <gsl/gsl_errno.h>
#include <gsl/gsl_interp.h>
static int
linear_init (void * vstate,
const double x_array[],
const double y_array[],
size_t size)
{
return GSL_SUCCESS;
}
static
int
linear_eval (const void * vstate,
const double x_array[], const double y_array[], size_t size,
double x,
gsl_interp_accel * a,
double *y)
{
double x_lo, x_hi;
double y_lo, y_hi;
double dx;
size_t index;
if (a != 0)
{
index = gsl_interp_accel_find (a, x_array, size, x);
}
else
{
index = gsl_interp_bsearch (x_array, x, 0, size - 1);
}
/* evaluate */
x_lo = x_array[index];
x_hi = x_array[index + 1];
y_lo = y_array[index];
y_hi = y_array[index + 1];
dx = x_hi - x_lo;
if (dx > 0.0)
{
*y = y_lo + (x - x_lo) / dx * (y_hi - y_lo);
return GSL_SUCCESS;
}
else
{
*y = 0.0;
return GSL_EINVAL;
}
}
static
int
linear_eval_deriv (const void * vstate,
const double x_array[], const double y_array[], size_t size,
double x,
gsl_interp_accel * a,
double *dydx)
{
double x_lo, x_hi;
double y_lo, y_hi;
double dx;
double dy;
size_t index;
if (a != 0)
{
index = gsl_interp_accel_find (a, x_array, size, x);
}
else
{
index = gsl_interp_bsearch (x_array, x, 0, size - 1);
}
/* evaluate */
x_lo = x_array[index];
x_hi = x_array[index + 1];
y_lo = y_array[index];
y_hi = y_array[index + 1];
dx = x_hi - x_lo;
dy = y_hi - y_lo;
if (dx > 0.0)
{
*dydx = dy / dx;;
return GSL_SUCCESS;
}
else
{
*dydx = 0.0;
return GSL_EINVAL;
}
}
static
int
linear_eval_deriv2 (const void * vstate,
const double x_array[], const double y_array[], size_t size,
double x,
gsl_interp_accel * a,
double *y_pp)
{
*y_pp = 0.0;
return GSL_SUCCESS;
}
static
int
linear_eval_integ (const void * vstate,
const double x_array[], const double y_array[], size_t size,
gsl_interp_accel * acc,
double a, double b,
double * result)
{
size_t i, index_a, index_b;
if (acc != 0)
{
index_a = gsl_interp_accel_find (acc, x_array, size, a);
index_b = gsl_interp_accel_find (acc, x_array, size, b);
}
else
{
index_a = gsl_interp_bsearch (x_array, a, 0, size - 1);
index_b = gsl_interp_bsearch (x_array, b, 0, size - 1);
}
/* endpoints span more than one interval */
*result = 0.0;
/* interior intervals */
for(i=index_a; i<=index_b; i++) {
const double x_hi = x_array[i + 1];
const double x_lo = x_array[i];
const double y_lo = y_array[i];
const double y_hi = y_array[i + 1];
const double dx = x_hi - x_lo;
if(dx != 0.0) {
if (i == index_a || i == index_b)
{
double x1 = (i == index_a) ? a : x_lo;
double x2 = (i == index_b) ? b : x_hi;
const double D = (y_hi-y_lo)/dx;
*result += (x2-x1) * (y_lo + 0.5*D*((x2-x_lo)+(x1-x_lo)));
}
else
{
*result += 0.5 * dx * (y_lo + y_hi);
}
}
}
return GSL_SUCCESS;
}
static const gsl_interp_type linear_type =
{
"linear",
2,
NULL, /* alloc, not applicable */
&linear_init,
&linear_eval,
&linear_eval_deriv,
&linear_eval_deriv2,
&linear_eval_integ,
NULL, /* free, not applicable */
};
const gsl_interp_type * gsl_interp_linear = &linear_type;
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