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/* interpolation/linear.c
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*
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* Copyright (C) 1996, 1997, 1998, 1999, 2000 Gerard Jungman
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or (at
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* your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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/* Author: G. Jungman
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*/
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#include <config.h>
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#include <stdlib.h>
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#include <gsl/gsl_errno.h>
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#include <gsl/gsl_interp.h>
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static int
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linear_init (void * vstate,
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const double x_array[],
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const double y_array[],
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size_t size)
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{
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return GSL_SUCCESS;
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}
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static
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int
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linear_eval (const void * vstate,
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const double x_array[], const double y_array[], size_t size,
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double x,
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gsl_interp_accel * a,
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double *y)
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{
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double x_lo, x_hi;
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double y_lo, y_hi;
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double dx;
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size_t index;
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if (a != 0)
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{
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index = gsl_interp_accel_find (a, x_array, size, x);
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}
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else
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{
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index = gsl_interp_bsearch (x_array, x, 0, size - 1);
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}
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/* evaluate */
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x_lo = x_array[index];
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x_hi = x_array[index + 1];
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y_lo = y_array[index];
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y_hi = y_array[index + 1];
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dx = x_hi - x_lo;
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if (dx > 0.0)
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{
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*y = y_lo + (x - x_lo) / dx * (y_hi - y_lo);
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return GSL_SUCCESS;
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}
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else
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{
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*y = 0.0;
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return GSL_EINVAL;
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}
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}
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static
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int
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linear_eval_deriv (const void * vstate,
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const double x_array[], const double y_array[], size_t size,
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double x,
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gsl_interp_accel * a,
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double *dydx)
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{
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double x_lo, x_hi;
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double y_lo, y_hi;
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double dx;
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double dy;
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size_t index;
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if (a != 0)
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{
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index = gsl_interp_accel_find (a, x_array, size, x);
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}
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else
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{
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index = gsl_interp_bsearch (x_array, x, 0, size - 1);
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}
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/* evaluate */
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x_lo = x_array[index];
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x_hi = x_array[index + 1];
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y_lo = y_array[index];
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y_hi = y_array[index + 1];
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dx = x_hi - x_lo;
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dy = y_hi - y_lo;
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if (dx > 0.0)
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{
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*dydx = dy / dx;;
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return GSL_SUCCESS;
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}
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else
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{
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*dydx = 0.0;
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return GSL_EINVAL;
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}
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}
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static
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int
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linear_eval_deriv2 (const void * vstate,
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const double x_array[], const double y_array[], size_t size,
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double x,
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gsl_interp_accel * a,
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double *y_pp)
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{
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*y_pp = 0.0;
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return GSL_SUCCESS;
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}
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static
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int
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linear_eval_integ (const void * vstate,
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const double x_array[], const double y_array[], size_t size,
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gsl_interp_accel * acc,
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double a, double b,
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double * result)
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{
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size_t i, index_a, index_b;
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if (acc != 0)
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{
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index_a = gsl_interp_accel_find (acc, x_array, size, a);
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index_b = gsl_interp_accel_find (acc, x_array, size, b);
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}
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else
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{
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index_a = gsl_interp_bsearch (x_array, a, 0, size - 1);
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index_b = gsl_interp_bsearch (x_array, b, 0, size - 1);
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}
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/* endpoints span more than one interval */
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*result = 0.0;
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/* interior intervals */
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for(i=index_a; i<=index_b; i++) {
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const double x_hi = x_array[i + 1];
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const double x_lo = x_array[i];
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const double y_lo = y_array[i];
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const double y_hi = y_array[i + 1];
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const double dx = x_hi - x_lo;
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if(dx != 0.0) {
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if (i == index_a || i == index_b)
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{
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double x1 = (i == index_a) ? a : x_lo;
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double x2 = (i == index_b) ? b : x_hi;
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const double D = (y_hi-y_lo)/dx;
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*result += (x2-x1) * (y_lo + 0.5*D*((x2-x_lo)+(x1-x_lo)));
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}
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else
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{
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*result += 0.5 * dx * (y_lo + y_hi);
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}
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}
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}
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return GSL_SUCCESS;
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}
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static const gsl_interp_type linear_type =
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{
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"linear",
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2,
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NULL, /* alloc, not applicable */
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&linear_init,
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&linear_eval,
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&linear_eval_deriv,
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&linear_eval_deriv2,
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&linear_eval_integ,
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NULL, /* free, not applicable */
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};
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const gsl_interp_type * gsl_interp_linear = &linear_type;
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