lineartransport.H

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/* Copyright 2022-2026 The Regents of the University of California, through Lawrence
 *           Berkeley National Laboratory (subject to receipt of any required
 *           approvals from the U.S. Dept. of Energy). All rights reserved.
 *
 * This file is part of ImpactX.
 *
 * Authors: Axel Huebl
 * License: BSD-3-Clause-LBNL
 */
#ifndef IMPACTX_ELEMENTS_MIXIN_LINEAR_TRANSPORT_H
#define IMPACTX_ELEMENTS_MIXIN_LINEAR_TRANSPORT_H
 
#include "particles/CovarianceMatrix.H"
 
#include <ablastr/constant.H>
 
#include <AMReX_Math.H>
#include <AMReX_Extension.H>
#include <AMReX_REAL.H>
#include <AMReX_SmallMatrix.H>
 
#include <stdexcept>
#include <string>
#include <type_traits>
 
 
namespace impactx::elements::mixin
{
    template <typename T_Element, bool Implemented = true>
    struct LinearTransport
    {
        static constexpr bool has_linear_transport = Implemented;

        AMREX_GPU_HOST AMREX_FORCE_INLINE
        void
        operator() (
            Map6x6 & AMREX_RESTRICT cm,
            RefPart const & AMREX_RESTRICT ref
        ) const
        {
            static_assert(
                std::is_base_of_v<LinearTransport, T_Element>,
                "LinearTransport can only be used as a mixin class!"
            );
 
            // small trick to force every derived class has to implement a method transport_map
            // (w/o using a purely virtual function)
            T_Element const & element = *static_cast<T_Element const*>(this);
            cm = element.transport_map(ref) * cm * element.transport_map(ref).transpose();
        }
    };

    template <typename T_Element>
    struct LinearTransport<T_Element, false>
    {
        static constexpr bool has_linear_transport = false;

        AMREX_GPU_HOST AMREX_FORCE_INLINE
        Map6x6
        transport_map ([[maybe_unused]] RefPart const & AMREX_RESTRICT refpart) const
        {
            throw std::runtime_error(
                std::string(T_Element::type)
                + ": Linear transport map is not yet implemented for this element."
            );
        }

        AMREX_GPU_HOST AMREX_FORCE_INLINE
        void
        operator() (
            Map6x6 & AMREX_RESTRICT cm,
            RefPart const & AMREX_RESTRICT ref
        ) const
        {
            static_assert(
                std::is_base_of_v<LinearTransport, T_Element>,
                "LinearTransport can only be used as a mixin class!"
            );
 
            T_Element const & element = *static_cast<T_Element const*>(this);
            cm = element.transport_map(ref) * cm * element.transport_map(ref).transpose();
        }
    };
 
} // namespace impactx::elements::mixin
 
#endif // IMPACTX_ELEMENTS_MIXIN_LINEAR_TRANSPORT_H