1 /* interpolation/integ_eval_macro.h
3 * Copyright (C) 1996, 1997, 1998, 1999, 2000 Gerard Jungman
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6 * it under the terms of the GNU General Public License as published by
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13 * General Public License for more details.
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17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
20 /* function for doing the spline integral evaluation
21 which is common to both the cspline and akima methods
25 integ_eval (double ai, double bi, double ci, double di, double xi, double a,
28 const double r1 = a - xi;
29 const double r2 = b - xi;
30 const double r12 = r1 + r2;
31 const double bterm = 0.5 * bi * r12;
32 const double cterm = (1.0 / 3.0) * ci * (r1 * r1 + r2 * r2 + r1 * r2);
33 const double dterm = 0.25 * di * r12 * (r1 * r1 + r2 * r2);
35 return (b - a) * (ai + bterm + cterm + dterm);