simpleGeomDecomp.C

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#include "simpleGeomDecomp.H"
#include "addToRunTimeSelectionTable.H"
#include "SortableList.H"
#include "globalIndex.H"
#include "SubField.H"

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

namespace Foam
{
    defineTypeNameAndDebug(simpleGeomDecomp, 0);

    addToRunTimeSelectionTable
    (
        decompositionMethod,
        simpleGeomDecomp,
        decomposer
    );

    addToRunTimeSelectionTable
    (
        decompositionMethod,
        simpleGeomDecomp,
        distributor
    );
}


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

// assignToProcessorGroup : given nCells cells and nProcGroup processor
// groups to share them, how do we share them out? Answer : each group
// gets nCells/nProcGroup cells, and the first few get one
// extra to make up the numbers. This should produce almost
// perfect load balancing

void Foam::simpleGeomDecomp::assignToProcessorGroup
(
    labelList& processorGroup,
    const label nProcGroup
) const
{
    label jump = processorGroup.size()/nProcGroup;
    label jumpb = jump + 1;
    label fstProcessorGroup = processorGroup.size() - jump*nProcGroup;

    label ind = 0;
    label j = 0;

    // assign cells to the first few processor groups (those with
    // one extra cell each
    for (j=0; j<fstProcessorGroup; j++)
    {
        for (label k=0; k<jumpb; k++)
        {
            processorGroup[ind++] = j;
        }
    }

    // and now to the `normal' processor groups
    for (; j<nProcGroup; j++)
    {
        for (label k=0; k<jump; k++)
        {
            processorGroup[ind++] = j;
        }
    }
}


void Foam::simpleGeomDecomp::assignToProcessorGroup
(
    labelList& processorGroup,
    const label nProcGroup,
    const labelList& indices,
    const scalarField& weights,
    const scalar summedWeights
) const
{
    // This routine gets the sorted points.
    // Easiest to explain with an example.
    // E.g. 400 points, sum of weights : 513.
    // Now with number of divisions in this direction (nProcGroup) : 4
    // gives the split at 513/4 = 128
    // So summed weight from 0..128 goes into bin 0,
    //     ,,              128..256 goes into bin 1
    //   etc.
    // Finally any remaining ones go into the last bin (3).

    const scalar jump = summedWeights/nProcGroup;
    const label nProcGroupM1 = nProcGroup - 1;
    scalar sumWeights = 0;
    label ind = 0;
    label j = 0;

    // assign cells to all except last group.
    for (j=0; j<nProcGroupM1; j++)
    {
        const scalar limit = jump*scalar(j + 1);
        while (sumWeights < limit)
        {
            sumWeights += weights[indices[ind]];
            processorGroup[ind++] = j;
        }
    }
    // Ensure last included.
    while (ind < processorGroup.size())
    {
       processorGroup[ind++] = nProcGroupM1;
    }
}


Foam::labelList Foam::simpleGeomDecomp::decomposeOneProc
(
    const pointField& points
) const
{
    // construct a list for the final result
    labelList finalDecomp(points.size());

    labelList processorGroups(points.size());

    labelList pointIndices(points.size());
    forAll(pointIndices, i)
    {
        pointIndices[i] = i;
    }

    const pointField rotatedPoints(rotDelta_ & points);

    // and one to take the processor group id's. For each direction.
    // we assign the processors to groups of processors labelled
    // 0..nX to give a banded structure on the mesh. Then we
    // construct the actual processor number by treating this as
    // the units part of the processor number.
    sort
    (
        pointIndices,
        UList<scalar>::less(rotatedPoints.component(vector::X))
    );

    assignToProcessorGroup(processorGroups, n_.x());

    forAll(points, i)
    {
        finalDecomp[pointIndices[i]] = processorGroups[i];
    }


    // now do the same thing in the Y direction. These processor group
    // numbers add multiples of nX to the proc. number (columns)
    sort
    (
        pointIndices,
        UList<scalar>::less(rotatedPoints.component(vector::Y))
    );

    assignToProcessorGroup(processorGroups, n_.y());

    forAll(points, i)
    {
        finalDecomp[pointIndices[i]] += n_.x()*processorGroups[i];
    }


    // finally in the Z direction. Now we add multiples of nX*nY to give
    // layers
    sort
    (
        pointIndices,
        UList<scalar>::less(rotatedPoints.component(vector::Z))
    );

    assignToProcessorGroup(processorGroups, n_.z());

    forAll(points, i)
    {
        finalDecomp[pointIndices[i]] += n_.x()*n_.y()*processorGroups[i];
    }

    return finalDecomp;
}


Foam::labelList Foam::simpleGeomDecomp::decomposeOneProc
(
    const pointField& points,
    const scalarField& weights
) const
{
    // construct a list for the final result
    labelList finalDecomp(points.size());

    labelList processorGroups(points.size());

    labelList pointIndices(points.size());
    forAll(pointIndices, i)
    {
        pointIndices[i] = i;
    }

    const pointField rotatedPoints(rotDelta_ & points);

    // and one to take the processor group id's. For each direction.
    // we assign the processors to groups of processors labelled
    // 0..nX to give a banded structure on the mesh. Then we
    // construct the actual processor number by treating this as
    // the units part of the processor number.
    sort
    (
        pointIndices,
        UList<scalar>::less(rotatedPoints.component(vector::X))
    );

    const scalar summedWeights = sum(weights);
    assignToProcessorGroup
    (
        processorGroups,
        n_.x(),
        pointIndices,
        weights,
        summedWeights
    );

    forAll(points, i)
    {
        finalDecomp[pointIndices[i]] = processorGroups[i];
    }


    // now do the same thing in the Y direction. These processor group
    // numbers add multiples of nX to the proc. number (columns)
    sort
    (
        pointIndices,
        UList<scalar>::less(rotatedPoints.component(vector::Y))
    );

    assignToProcessorGroup
    (
        processorGroups,
        n_.y(),
        pointIndices,
        weights,
        summedWeights
    );

    forAll(points, i)
    {
        finalDecomp[pointIndices[i]] += n_.x()*processorGroups[i];
    }


    // finally in the Z direction. Now we add multiples of nX*nY to give
    // layers
    sort
    (
        pointIndices,
        UList<scalar>::less(rotatedPoints.component(vector::Z))
    );

    assignToProcessorGroup
    (
        processorGroups,
        n_.z(),
        pointIndices,
        weights,
        summedWeights
    );

    forAll(points, i)
    {
        finalDecomp[pointIndices[i]] += n_.x()*n_.y()*processorGroups[i];
    }

    return finalDecomp;
}


// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //

Foam::simpleGeomDecomp::simpleGeomDecomp(const dictionary& decompositionDict)
:
    geomDecomp(decompositionDict, typeName)
{}


// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //

Foam::labelList Foam::simpleGeomDecomp::decompose
(
    const pointField& points
)
{
    if (!Pstream::parRun())
    {
        return decomposeOneProc(points);
    }
    else
    {
        globalIndex globalNumbers(points.size());

        // Collect all points on master
        if (Pstream::master())
        {
            pointField allPoints(globalNumbers.size());

            label nTotalPoints = 0;
            // Master first
            SubField<point>(allPoints, points.size()) = points;
            nTotalPoints += points.size();

            // Add slaves
            for (int slave=1; slave<Pstream::nProcs(); slave++)
            {
                IPstream fromSlave(Pstream::commsTypes::scheduled, slave);
                pointField nbrPoints(fromSlave);
                SubField<point>
                (
                    allPoints,
                    nbrPoints.size(),
                    nTotalPoints
                ) = nbrPoints;
                nTotalPoints += nbrPoints.size();
            }

            // Decompose
            labelList finalDecomp(decomposeOneProc(allPoints));

            // Send back
            for (int slave=1; slave<Pstream::nProcs(); slave++)
            {
                OPstream toSlave(Pstream::commsTypes::scheduled, slave);
                toSlave << SubField<label>
                (
                    finalDecomp,
                    globalNumbers.localSize(slave),
                    globalNumbers.offset(slave)
                );
            }
            // Get my own part
            finalDecomp.setSize(points.size());

            return finalDecomp;
        }
        else
        {
            // Send my points
            {
                OPstream toMaster
                (
                    Pstream::commsTypes::scheduled,
                    Pstream::masterNo()
                );
                toMaster<< points;
            }

            // Receive back decomposition
            IPstream fromMaster
            (
                Pstream::commsTypes::scheduled,
                Pstream::masterNo()
            );
            labelList finalDecomp(fromMaster);

            return finalDecomp;
        }
    }
}


Foam::labelList Foam::simpleGeomDecomp::decompose
(
    const pointField& points,
    const scalarField& weights
)
{
    if (!Pstream::parRun())
    {
        return decomposeOneProc(points, weights);
    }
    else
    {
        globalIndex globalNumbers(points.size());

        // Collect all points on master
        if (Pstream::master())
        {
            pointField allPoints(globalNumbers.size());
            scalarField allWeights(allPoints.size());

            label nTotalPoints = 0;
            // Master first
            SubField<point>(allPoints, points.size()) = points;
            SubField<scalar>(allWeights, points.size()) = weights;
            nTotalPoints += points.size();

            // Add slaves
            for (int slave=1; slave<Pstream::nProcs(); slave++)
            {
                IPstream fromSlave(Pstream::commsTypes::scheduled, slave);
                pointField nbrPoints(fromSlave);
                scalarField nbrWeights(fromSlave);
                SubField<point>
                (
                    allPoints,
                    nbrPoints.size(),
                    nTotalPoints
                ) = nbrPoints;
                SubField<scalar>
                (
                    allWeights,
                    nbrWeights.size(),
                    nTotalPoints
                ) = nbrWeights;
                nTotalPoints += nbrPoints.size();
            }

            // Decompose
            labelList finalDecomp(decomposeOneProc(allPoints, allWeights));

            // Send back
            for (int slave=1; slave<Pstream::nProcs(); slave++)
            {
                OPstream toSlave(Pstream::commsTypes::scheduled, slave);
                toSlave << SubField<label>
                (
                    finalDecomp,
                    globalNumbers.localSize(slave),
                    globalNumbers.offset(slave)
                );
            }
            // Get my own part
            finalDecomp.setSize(points.size());

            return finalDecomp;
        }
        else
        {
            // Send my points
            {
                OPstream toMaster
                (
                    Pstream::commsTypes::scheduled,
                    Pstream::masterNo()
                );
                toMaster<< points << weights;
            }

            // Receive back decomposition
            IPstream fromMaster
            (
                Pstream::commsTypes::scheduled,
                Pstream::masterNo()
            );
            labelList finalDecomp(fromMaster);

            return finalDecomp;
        }
    }
}


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