backwardEuler.hpp

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// SPDX-License-Identifier: MIT
//
// SPDX-FileCopyrightText: 2023 NeoN authors
 
#pragma once
 
#include "NeoN/core/database/fieldCollection.hpp"
#include "NeoN/core/database/oldTimeCollection.hpp"
#include "NeoN/fields/field.hpp"
#include "NeoN/timeIntegration/timeIntegration.hpp"
#include "NeoN/dsl/solver.hpp"
 
#include "NeoN/linearAlgebra/linearSystem.hpp"
 
// TODO decouple from fvcc
#include "NeoN/finiteVolume/cellCentred/linearAlgebra/sparsityPattern.hpp"
 
 
namespace NeoN::timeIntegration
{
 
template<typename SolutionVectorType>
class BackwardEuler :
    public TimeIntegratorBase<SolutionVectorType>::template Register<
        BackwardEuler<SolutionVectorType>>
{
 
public:
 
    using ValueType = typename SolutionVectorType::VectorValueType;
    using Base = TimeIntegratorBase<SolutionVectorType>::template Register<
        BackwardEuler<SolutionVectorType>>;
 
    BackwardEuler(const Dictionary& schemeDict, const Dictionary& solutionDict)
        : Base(schemeDict, solutionDict)
    {}
 
    static std::string name() { return "backwardEuler"; }
 
    static std::string doc() { return "first order time integration method"; }
 
    static std::string schema() { return "none"; }
 
    void solve(
        dsl::Expression<ValueType>& eqn,
        SolutionVectorType& solutionVector,
        [[maybe_unused]] scalar t,
        scalar dt
    ) override
    {
        auto source = eqn.explicitOperation(solutionVector.size());
        SolutionVectorType& oldSolutionVector = finiteVolume::cellCentred::oldTime(solutionVector);
 
        // solutionVector.internalVector() = oldSolutionVector.internalVector() - source * dt;
        // solutionVector.correctBoundaryConditions();
        // solve sparse matrix system
        // using ValueType = typename SolutionVectorType::ElementType;
 
        // TODO decouple from fvcc specific implementation
        auto sparsity = NeoN::finiteVolume::cellCentred::SparsityPattern(solutionVector.mesh());
        auto ls = la::createEmptyLinearSystem<
            ValueType,
            localIdx,
            finiteVolume::cellCentred::SparsityPattern>(sparsity);
 
        eqn.implicitOperation(ls);
 
        auto values = ls.matrix().values();
        eqn.implicitOperation(ls, t, dt);
 
        auto solver = NeoN::la::Solver(solutionVector.exec(), this->solutionDict_);
        solver.solve(ls, solutionVector.internalVector());
 
        // check if executor is GPU
        if (std::holds_alternative<NeoN::GPUExecutor>(eqn.exec()))
        {
            Kokkos::fence();
        }
        oldSolutionVector.internalVector() = solutionVector.internalVector();
    };
 
    std::unique_ptr<TimeIntegratorBase<SolutionVectorType>> clone() const override
    {
        return std::make_unique<BackwardEuler>(*this);
    }
};
 
 
} // namespace NeoN