data/applications/test/ODE/Test-ODE.C

/*---------------------------------------------------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Copyright (C) 2011-2019 OpenFOAM Foundation
     \\/     M anipulation  |
-------------------------------------------------------------------------------
License
    This file is part of OpenFOAM.

    OpenFOAM is free software: you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    for more details.

    You should have received a copy of the GNU General Public License
    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.

Description

\*---------------------------------------------------------------------------*/

#include "argList.H"
#include "IOmanip.H"
#include "ODESystem.H"
#include "ODESolver.H"

using namespace Foam;

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

class testODE
:
    public ODESystem
{

public:

    testODE()
    {}

    label nEqns() const
    {
        return 4;
    }

    void derivatives
    (
        const scalar x,
        const scalarField& y,
        const label li,
        scalarField& dydx
    ) const
    {
        dydx[0] = -y[1];
        dydx[1] = y[0] - (1.0/x)*y[1];
        dydx[2] = y[1] - (2.0/x)*y[2];
        dydx[3] = y[2] - (3.0/x)*y[3];
    }

    void jacobian
    (
        const scalar x,
        const scalarField& y,
        const label li,
        scalarField& dfdx,
        scalarSquareMatrix& dfdy
    ) const
    {
        dfdx[0] = 0.0;
        dfdx[1] = (1.0/sqr(x))*y[1];
        dfdx[2] = (2.0/sqr(x))*y[2];
        dfdx[3] = (3.0/sqr(x))*y[3];

        dfdy(0, 0) = 0.0;
        dfdy(0, 1) = -1.0;
        dfdy(0, 2) = 0.0;
        dfdy(0, 3) = 0.0;

        dfdy(1, 0) = 1.0;
        dfdy(1, 1) = -1.0/x;
        dfdy(1, 2) = 0.0;
        dfdy(1, 3) = 0.0;

        dfdy(2, 0) = 0.0;
        dfdy(2, 1) = 1.0;
        dfdy(2, 2) = -2.0/x;
        dfdy(2, 3) = 0.0;

        dfdy(3, 0) = 0.0;
        dfdy(3, 1) = 0.0;
        dfdy(3, 2) = 1.0;
        dfdy(3, 3) = -3.0/x;
    }
};


// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
// Main program:

int main(int argc, char *argv[])
{
    argList::validArgs.append("ODESolver");
    argList args(argc, argv);

    // Create the ODE system
    testODE ode;

    dictionary dict;
    dict.add("solver", args[1]);

    // Create the selected ODE system solver
    autoPtr<ODESolver> odeSolver = ODESolver::New(ode, dict);

    // Initialise the ODE system fields
    scalar xStart = 1.0;
    scalarField yStart(ode.nEqns());
    yStart[0] = ::Foam::j0(xStart);
    yStart[1] = ::Foam::j1(xStart);
    yStart[2] = ::Foam::jn(2, xStart);
    yStart[3] = ::Foam::jn(3, xStart);

    // Print the evolution of the solution and the time-step
    scalarField dyStart(ode.nEqns());
    ode.derivatives(xStart, yStart, 0, dyStart);

    Info<< setw(10) << "relTol" << setw(12) << "dxEst";
    Info<< setw(13) << "dxDid" << setw(14) << "dxNext" << endl;
    Info<< setprecision(6);

    for (label i=0; i<15; i++)
    {
        scalar relTol = ::Foam::exp(-scalar(i + 1));

        scalar x = xStart;
        scalarField y(yStart);

        scalar dxEst = 0.6;
        scalar dxNext = dxEst;

        odeSolver->relTol() = relTol;
        odeSolver->solve(x, y, 0, dxNext);

        Info<< scientific << setw(13) << relTol;
        Info<< fixed << setw(11) << dxEst;
        Info<< setw(13) << x - xStart << setw(13) << dxNext
            << setw(13) << y[0] << setw(13) << y[1]
            << setw(13) << y[2] << setw(13) << y[3]
            << endl;
    }

    scalar x = xStart;
    scalar xEnd = x + 1.0;
    scalarField y(yStart);

    scalarField yEnd(ode.nEqns());
    yEnd[0] = ::Foam::j0(xEnd);
    yEnd[1] = ::Foam::j1(xEnd);
    yEnd[2] = ::Foam::jn(2, xEnd);
    yEnd[3] = ::Foam::jn(3, xEnd);

    scalar dxEst = 0.5;

    odeSolver->relTol() = 1e-4;
    odeSolver->solve(x, xEnd, y, 0, dxEst);

    Info<< nl << "Analytical: y(2.0) = " << yEnd << endl;
    Info      << "Numerical:  y(2.0) = " << y << ", dxEst = " << dxEst << endl;

    Info<< "\nEnd\n" << endl;

    return 0;
}


// ************************************************************************* //