foam-extend4.1-coherent-io/applications/solvers/basic/potentialFoam/createFields.H

    Info<< "Reading field p\n" << endl;
    volScalarField p
    (
        IOobject
        (
            "p",
            runTime.timeName(),
            mesh,
            IOobject::MUST_READ,
            IOobject::NO_WRITE
        ),
        mesh
    );

    p = dimensionedScalar("zero", p.dimensions(), 0.0);


    Info<< "Reading field U\n" << endl;
    volVectorField U
    (
        IOobject
        (
            "U",
            runTime.timeName(),
            mesh,
            IOobject::MUST_READ,
            IOobject::AUTO_WRITE
        ),
        mesh
    );

    U = dimensionedVector("0", U.dimensions(), vector::zero);

    surfaceScalarField phi
    (
        IOobject
        (
            "phi",
            runTime.timeName(),
            mesh,
            IOobject::NO_READ,
            IOobject::AUTO_WRITE
        ),
        fvc::interpolate(U) & mesh.Sf()
    );


    label pRefCell = 0;
    scalar pRefValue = 0.0;
    setRefCell(p, mesh.solutionDict().subDict("SIMPLE"), pRefCell, pRefValue);