mirror of https://github.com/ArduPilot/ardupilot
72 lines
2.0 KiB
C++
72 lines
2.0 KiB
C++
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/*
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* spline5.cpp
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*
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* Created by William Geyer and Chris Olson modified for ardupilot
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* Original work by Ryan Muller
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* https://gist.github.com/ryanthejuggler/4132103
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* released under the Creative Commons CC0 License
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* http://creativecommons.org/publicdomain/zero/1.0/
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*
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* This file is free software: you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by the
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* Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This file 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.
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* See the GNU 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 along
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* with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <stdint.h>
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#include "spline5.h"
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void splinterp5(const float x[5], float out[4][4])
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{
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// number of spline points
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const uint8_t n = 5;
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// working variables
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float u[n] {};
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// second derivative
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// additional element in array necessary for back substitution loop.
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float z[n+1] {};
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// set the second derivative to 0 at the ends
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z[0] = u[0] = 0;
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z[n-1] = 0;
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// decomposition loop
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for (uint8_t i=1; i<n-1; i++) {
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float p = 0.5f * z[i-1] + 2.0f;
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// keep p from ever becoming zero
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if (p < 0.01f && p >= 0.0f) {
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p = 0.01f;
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} else if (p > -0.01f && p < 0.0f) {
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p = -0.01f;
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}
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float p_inv = 1.0f / p;
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z[i] = -0.5f * p_inv;
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u[i] = x[i+1] + x[i-1] - 2.0f * x[i];
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u[i] = (3.0f * u[i] - 0.5f * u[i-1]) * p_inv;
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}
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// back-substitution loop
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for (uint8_t i=n-1; i>0; i--) {
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z[i] = z[i] * z[i+1] + u[i];
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}
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for (uint8_t i=0; i<n-1; i++) {
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out[i][0] = x[i+1];
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out[i][1] = x[i];
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out[i][2] = z[i+1];
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out[i][3] = z[i];
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}
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}
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