cubic_spline.h

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//
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Copyright (C) 2020 - 2025 by the ryujin authors
//
 
#pragma once
 
#include <compile_time_options.h>
 
#ifdef DEAL_II_WITH_GSL
#include <gsl/gsl_spline.h>
 
namespace ryujin
{
  class CubicSpline
  {
  public:
    CubicSpline(const std::vector<double> &x,
                const std::vector<double> &y) noexcept
        : x_(x)
        , y_(y)
    {
      AssertNothrow(x_.size() == y_.size(), dealii::ExcInternalError());
      AssertNothrow(x_.size() >= 2, dealii::ExcInternalError());
      AssertNothrow(std::is_sorted(x_.begin(), x_.end()),
                    dealii::ExcInternalError());
 
      spline = gsl_spline_alloc(gsl_interp_cspline, x_.size());
      gsl_spline_init(spline, x_.data(), y_.data(), x_.size());
 
      accel = gsl_interp_accel_alloc();
    }
 
    CubicSpline(const CubicSpline &copy)
        : CubicSpline(copy.x_, copy.y_)
    {
    }
 
    CubicSpline &operator=(const CubicSpline &) = delete;
 
    ~CubicSpline()
    {
      gsl_interp_accel_free(accel);
      gsl_spline_free(spline);
    }
 
    inline double eval(double x) const
    {
      return gsl_spline_eval(spline, x, accel);
    }
 
  private:
    const std::vector<double> x_;
    const std::vector<double> y_;
    gsl_spline *spline;
    mutable gsl_interp_accel *accel;
  };
} // namespace ryujin
 
#endif