SplineBisection.h

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//                   OpenMS -- Open-Source Mass Spectrometry
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// Copyright The OpenMS Team -- Eberhard Karls University Tuebingen,
// ETH Zurich, and Freie Universitaet Berlin 2002-2020.
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// $Maintainer: Hannes Roest $
// $Authors: Hannes Roest $
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#pragma once
 
#include <OpenMS/config.h>
 
#include <limits> 
#include <cmath> 
 
namespace OpenMS
{
  namespace Math
  {
 
    template <class T>
    void spline_bisection(const T & peak_spline, 
        double const left_neighbor_mz,
        double const right_neighbor_mz,
        double & max_peak_mz,
        double & max_peak_int,
        double const threshold = 1e-6)
    {
      // calculate maximum by evaluating the spline's 1st derivative
      // (bisection method)
      double lefthand = left_neighbor_mz;
      double righthand = right_neighbor_mz;
 
      bool lefthand_sign = 1;
      double eps = std::numeric_limits<double>::epsilon();
 
      // bisection
      do
      {
        double mid = (lefthand + righthand) / 2.0;
        double midpoint_deriv_val = peak_spline.derivatives(mid, 1);
 
        // if deriv nearly zero then maximum already found
        if (!(std::fabs(midpoint_deriv_val) > eps))
        {
          break;
        }
 
        bool midpoint_sign = (midpoint_deriv_val < 0.0) ? 0 : 1;
 
        if (lefthand_sign ^ midpoint_sign)
        {
          righthand = mid;
        }
        else
        {
          lefthand = mid;
        }
      }
      while (righthand - lefthand > threshold);
 
      max_peak_mz = (lefthand + righthand) / 2;
      max_peak_int = peak_spline.eval(max_peak_mz);
    }
 
  }
}