splineInterpolate.cc

// -*- LSST-C++ -*-

/*
 * LSST Data Management System
 * Copyright 2008, 2009, 2010 LSST Corporation.
 *
 * This product includes software developed by the
 * LSST Project (http://www.lsst.org/).
 *
 * 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 3 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 LSST License Statement and
 * the GNU General Public License along with this program.  If not,
 * see <http://www.lsstcorp.org/LegalNotices/>.
 */

#include <iostream>
#include <cmath>
#include <vector>

#include <memory>
#include "lsst/afw/math/Interpolate.h"

using namespace std;
namespace math = lsst::afw::math;

int main() {
    // create x,y vector<>s containing a sin() function
    int const nX = 20;
    vector<double> x(nX);
    vector<double> y(nX);
    double const xLo = 0;
    double const xHi = 2.0 * M_PI;
    double const range = xHi - xLo;

    for (int i = 0; i < nX; ++i) {
        x[i] = xLo + static_cast<double>(i) / (nX - 1) * range;
        y[i] = sin(x[i]);
    }

    // create a new x vector<> on a different grid and extending beyond the bounds
    //   of the interpolation range to tests extrapolation properties
    int const nX2 = 100;
    vector<double> x2(nX2);
    for (int i = 0; i < nX2; ++i) {
        x2[i] = xLo + (((nX + 2.0) / nX) * static_cast<double>(i) / (nX2 - 1) - 1.0 / nX) * range;
    }

    // declare an spline interpolate object.  the constructor computes the first derivatives
    std::shared_ptr<math::Interpolate> yinterpS = math::makeInterpolate(x, y, math::Interpolate::LINEAR);

    // declare a linear interpolate object. the constructor computes the second derivatives
    std::shared_ptr<math::Interpolate> yinterpL =
            math::makeInterpolate(x, y, math::Interpolate::CUBIC_SPLINE);

    // output the interpolated y values, 1st derivatives, and 2nd derivatives.
    for (int i = 0; i < nX2; ++i) {
        cout << i << " " << x2[i] << " " << yinterpL->interpolate(x2[i]) << " "
             << yinterpS->interpolate(x2[i]) << " " << endl;
    }

    return 0;
}