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/* interpolation/integ_eval_macro.h
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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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/* function for doing the spline integral evaluation
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which is common to both the cspline and akima methods
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*/
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static inline double
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integ_eval (double ai, double bi, double ci, double di, double xi, double a,
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double b)
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{
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const double r1 = a - xi;
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const double r2 = b - xi;
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const double r12 = r1 + r2;
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const double bterm = 0.5 * bi * r12;
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const double cterm = (1.0 / 3.0) * ci * (r1 * r1 + r2 * r2 + r1 * r2);
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const double dterm = 0.25 * di * r12 * (r1 * r1 + r2 * r2);
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return (b - a) * (ai + bterm + cterm + dterm);
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}
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