text: #ifndef OPENMM_SPLINEFITTER_H_
  #define OPENMM_SPLINEFITTER_H_
  
  /* -------------------------------------------------------------------------- *
   *                                   OpenMM                                   *
   * -------------------------------------------------------------------------- *
   * This is part of the OpenMM molecular simulation toolkit originating from   *
   * Simbios, the NIH National Center for Physics-Based Simulation of           *
   * Biological Structures at Stanford, funded under the NIH Roadmap for        *
   * Medical Research, grant U54 GM072970. See https://simtk.org.               *
   *                                                                            *
   * Portions copyright (c) 2010 Stanford University and the Authors.           *
   * Authors: Peter Eastman                                                     *
   * Contributors:                                                              *
   *                                                                            *
   * Permission is hereby granted, free of charge, to any person obtaining a    *
   * copy of this software and associated documentation files (the "Software"), *
   * to deal in the Software without restriction, including without limitation  *
   * the rights to use, copy, modify, merge, publish, distribute, sublicense,   *
   * and/or sell copies of the Software, and to permit persons to whom the      *
   * Software is furnished to do so, subject to the following conditions:       *
   *                                                                            *
   * The above copyright notice and this permission notice shall be included in *
   * all copies or substantial portions of the Software.                        *
   *                                                                            *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR *
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,   *
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL    *
   * THE AUTHORS, CONTRIBUTORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,    *
   * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR      *
   * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE  *
   * USE OR OTHER DEALINGS IN THE SOFTWARE.                                     *
   * -------------------------------------------------------------------------- */
  
  #include "windowsExport.h"
  #include <vector>
  
  namespace OpenMM {
  
  /**
   * SplineFitter provides routines for performing cubic spline interpolation.
   */
  
  class OPENMM_EXPORT SplineFitter {
  public:
      /**
       * Fit a natural cubic spline to a set of data points.  The resulting spline interpolates all the
       * data points, has a continuous second derivative everywhere, and has a second derivative of 0 at
       * its end points.
       *
       * @param x      the values of the independent variable at the data points to interpolate.  They must
       *               be strictly increasing: x[i] > x[i-1].
       * @param y      the values of the dependent variable at the data points to interpolate
       * @param deriv  on exit, this contains the second derivative of the spline at each of the data points
       */
      static void createNaturalSpline(const std::vector<double>& x, const std::vector<double>& y, std::vector<double>& deriv);
      /**
       * Fit a periodic cubic spline to a set of data points.  The resulting spline interpolates all the
       * data points, has a continuous second derivative everywhere, and has identical second derivatives
       * at the end points.
       *
       * @param x      the values of the independent variable at the data points to interpolate.  They must
       *               be strictly increasing: x[i] > x[i-1].
       * @param y      the values of the dependent variable at the data points to interpolate.  The first and
       *               last entries must be identical.
       * @param deriv  on exit, this contains the second derivative of the spline at each of the data points
       */
      static void createPeriodicSpline(const std::vector<double>& x, const std::vector<double>& y, std::vector<double>& deriv);
      /**
       * Evaluate a spline generated by one of the other methods in this class.
       *
       * @param x     the values of the independent variable at the data points to interpolate
       * @param y     the values of the dependent variable at the data points to interpolate
       * @param deriv the vector of second derivatives that was calculated by one of the other methods
       * @param t     the value of the independent variable at which to evaluate the spline
       * @return the value of the spline at the specified point
       */
      static double evaluateSpline(const std::vector<double>& x, const std::vector<double>& y, const std::vector<double>& deriv, double t);
      /**
       * Evaluate the derivative of a spline generated by one of the other methods in this class.
       *
       * @param x     the values of the independent variable at the data points to interpolate
       * @param y     the values of the dependent variable at the data points to interpolate
       * @param deriv the vector of second derivatives that was calculated by one of the other methods
       * @param t     the value of the independent variable at which to evaluate the spline
       * @return the value of the spline's derivative  at the specified point
       */
      static double evaluateSplineDerivative(const std::vector<double>& x, const std::vector<double>& y, const std::vector<double>& deriv, double t);
  private:
      static void solveTridiagonalMatrix(const std::vector<double>& a, const std::vector<double>& b, const std::vector<double>& c, const std::vector<double>& rhs, std::vector<double>& sol);
  };
  
  } // namespace OpenMM
  
  #endif /*OPENMM_SPLINEFITTER_H_*/
  