riemann_rusanov.hpp

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// -------------------------------------------------------//
//
// SHAMROCK code for hydrodynamics
// Copyright (c) 2021-2026 Timothée David--Cléris <tim.shamrock@proton.me>
// SPDX-License-Identifier: CeCILL Free Software License Agreement v2.1
// Shamrock is licensed under the CeCILL 2.1 License, see LICENSE for more information
//
// -------------------------------------------------------//
 
#pragma once

 
#include "shammath/riemann_common.hpp"
 
namespace shammath {

    template<FluidStateSpec FSpec>
    inline constexpr typename FSpec::Tcons rusanov_flux(
        const FSpec &fspec,
        const typename FSpec::Tprim &prim_l,
        const typename FSpec::Tprim &prim_r,
        const typename FSpec::Tvec &n) {
        const auto cs_l = fspec.sound_speed(prim_l);
        const auto cs_r = fspec.sound_speed(prim_r);
 
        const auto vn_l = fspec.vn(prim_l, n);
        const auto vn_r = fspec.vn(prim_r, n);
 
        // NOLINTBEGIN(readability-identifier-naming)
 
        // Equation (10.56) from Toro 3rd Edition , Springer 2009
        const auto S = sham::max((sham::abs(vn_l) + cs_l), (sham::abs(vn_r) + cs_r));
 
        // NOLINTEND(readability-identifier-naming)
 
        const auto f_l = fspec.flux(prim_l, n, vn_l);
        const auto f_r = fspec.flux(prim_r, n, vn_r);
 
        const auto cons_l = fspec.prim_to_cons(prim_l);
        const auto cons_r = fspec.prim_to_cons(prim_r);
 
        // Equation (10.55) from Toro 3rd Edition , Springer 2009
        return 0.5 * ((f_l + f_r) - (cons_r - cons_l) * S);
    }
 
} // namespace shammath