AbstractSpline.h

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//
// Cubic Spline Interpolation to replace GSL spline
//
// Copyright (c) 2023, Paul Scherrer Institute, Villigen PSI, Switzerland
// All rights reserved
//
// This file is part of OPAL.
//
// OPAL 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.
//
// You should have received a copy of the GNU General License
// along with OPAL. If not, see <https://www.gnu.org/licenses/>.
//
 
#ifndef OPALX_ABSTRACTSPLINE_H
#define OPALX_ABSTRACTSPLINE_H
 
#include <vector>
#include "OPALTypes.h"
 
class AbstractSpline {
public:
    AbstractSpline() = default;
 
    virtual ~AbstractSpline() = default;
 
    // Accelerator for repeated evaluations (compatible with GSL interface)
    class Accelerator {
    public:
        Accelerator() = default;
        size_t last_index_{};
        size_t last_upper_index_{};
        void reset() {
            last_index_       = 0;
            last_upper_index_ = 0;
        }
    };
 
    virtual void init(const std::vector<double>& x, const std::vector<double>& y);
 
    virtual double eval(double x, Accelerator& accel) const = 0;
 
    virtual double evalIntegral(double xa, double xb, Accelerator& accel) const = 0;
 
protected:
    size_t findInterval(double x, size_t& intervalCache) const;
 
    // Members
    std::vector<double> x_{};
    std::vector<double> y_{};
};
 
#endif  // OPALX_ABSTRACTSPLINE_H