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#ifndef COSMOINTERFACE_DEFINITIONS_FIXEDBACKGROUNDEXPANSION_H
#define COSMOINTERFACE_DEFINITIONS_FIXEDBACKGROUNDEXPANSION_H

/* This file is part of CosmoLattice, available at www.cosmolattice.net .
   Copyright Daniel G. Figueroa, Adrien Florio, Francisco Torrenti and Wessel Valkenburg.
   Released under the MIT license, see LICENSE.md. */

// File info: Main contributor(s): Daniel G. Figueroa, Adrien Florio, Francisco Torrenti,  Year: 2021

#include "CosmoInterface/runparameters.h"

namespace TempLat
{
  template <typename T> class FixedBackgroundExpansion
  {
  public:
    // Put public methods here. These should change very little over time.
    template <class Model> FixedBackgroundExpansion(Model &model, RunParameters<T> &rPar):
    pEoS(2.0 / (3.0 * (1.0 + rPar.omegaEoS) - 2.0 * model.alpha)), // Coefficient of the power-law expansion: depends on EoS and alpha
    H0( (AlmostEqual(rPar.H0, 0.0) && Model::DefectsModel) ? pEoS / rPar.t0 : rPar.H0 / model.omegaStar), // Initial Hubble parameter (in program units)
    alpha(model.alpha),
    doResolutionPreserving(rPar.doResolutionPreserving),
    t0(rPar.t0),
    tRP0(rPar.tRP0),
    tRPMax(rPar.tRPMax),
    sRP(rPar.sRP)
    {
       if(AlmostEqual(H0, 0.0) && rPar.fixedBackground) throw(RunParametersInconsistent("For models that do not involve cosmic defects, you need to specify a non-zero H0 to run a simulation with fixed background. If you want to disable expansion, please set expansion = false in the input file."));
    }

    auto operator()(T deltaT) // Scale factor
    {
      return pow(1 + H0 / pEoS * deltaT, pEoS);
    }

    auto dot(T deltaT) // Scale factor time-derivative
    {
      return H0 * pow(1 + H0 / pEoS * deltaT, pEoS - 1);
    }

    auto const areWeResolutionPreserving() const {
      return doResolutionPreserving;
    }

    auto R(T deltaT) // Ricci scalar for NMC field evolution in fixed background expansion
    {
      return -6.0 * pow<2>(H0) * pEoS * pow(1 + H0 / pEoS * deltaT, -2.0 * alpha * pEoS) * (1 + pEoS * (alpha-2)) / pow<2>(pEoS + H0 * deltaT);
    }

  private:
    /* Put all member variables and private methods here. These may change arbitrarily. */

    T pEoS;
    T H0;
    T alpha;
    bool doResolutionPreserving;

  public:

    const T t0, tRP0, tRPMax, sRP;

  };

} // namespace TempLat

#endif