ptscotchDecomp.C

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/*---------------------------------------------------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     |
    \\  /    A nd           | Copyright (C) 2011-2015 OpenFOAM Foundation
     \\/     M anipulation  | Copyright (C) 2015 OpenCFD Ltd.
-------------------------------------------------------------------------------
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/>.
 
    From scotch forum:
 
    By: Francois PELLEGRINI RE: Graph mapping 'strategy' string [ reply ]
    2008-08-22 10:09 Strategy handling in Scotch is a bit tricky. In order
    not to be confused, you must have a clear view of how they are built.
    Here are some rules:
 
    1- Strategies are made up of "methods" which are combined by means of
    "operators".
 
    2- A method is of the form "m{param=value,param=value,...}", where "m"
    is a single character (this is your first error: "f" is a method name,
    not a parameter name).
 
    3- There exist different sort of strategies : bipartitioning strategies,
    mapping strategies, ordering strategies, which cannot be mixed. For
    instance, you cannot build a bipartitioning strategy and feed it to a
    mapping method (this is your second error).
 
    To use the "mapCompute" routine, you must create a mapping strategy, not
    a bipartitioning one, and so use stratGraphMap() and not
    stratGraphBipart(). Your mapping strategy should however be based on the
    "recursive bipartitioning" method ("b"). For instance, a simple (and
    hence not very efficient) mapping strategy can be :
 
    "b{sep=f}"
 
    which computes mappings with the recursive bipartitioning method "b",
    this latter using the Fiduccia-Mattheyses method "f" to compute its
    separators.
 
    If you want an exact partition (see your previous post), try
    "b{sep=fx}".
 
    However, these strategies are not the most efficient, as they do not
    make use of the multi-level framework.
 
    To use the multi-level framework, try for instance:
 
    "b{sep=m{vert=100,low=h,asc=f}x}"
 
    The current default mapping strategy in Scotch can be seen by using the
    "-vs" option of program dgpart. It is, to date:
 
    r
    {
        sep=m
        {
            asc=b
            {
                width=3,
                bnd=(d{pass=40,dif=1,rem=0,type=b}|)
                q{strat=f{move=80,pass=-1,bal=0.01,type=b}}
                x{sbbt=5,bal=0.05},
                org=q{strat=f{move=80,pass=-1,bal=0.01,type=b}}
                x{sbbt=5,bal=0.05}
            },
            low=q
            {
                strat=
                (
                    m
                    {
                        asc=b
                        {
                            bnd=(d{pass=40,type=b}|)
                            f{move=80,pass=-1,bal=0.05,type=b},
                            org=f{move=80,pass=-1,bal=0.05,type=b},
                            width=3
                        },
                        low=h{pass=10}
                        f{move=80,pass=-1,bal=0.05,type=b},
                        vert=80,
                        rat=0.8
                    }
                   |m
                    {
                        asc=b
                        {
                            bnd=(d{pass=40,type=b}|)
                            f{move=80,pass=-1,bal=0.05,type=b},
                            org=f{move=80,pass=-1,bal=0.05,type=b},
                            width=3
                        },
                        low=h{pass=10}
                        f{move=80,pass=-1,bal=0.05,type=b},
                        vert=80,
                        rat=0.8
                    }
                )
            },
            seq=q
            {
                strat=
                (
                    m
                    {
                        asc=b
                        {
                            bnd=(d{pass=40,type=b}|)
                            f{move=80,pass=-1,bal=0.05,type=b},
                            org=f{move=80,pass=-1,bal=0.05,type=b},
                            width=3
                        },
                        low=h{pass=10}
                        f{move=80,pass=-1,bal=0.05,type=b},
                        vert=80,
                        rat=0.8
                    }
                   |m
                    {
                        asc=b
                        {
                            bnd=(d{pass=40,type=b}|)
                            f{move=80,pass=-1,bal=0.05,type=b},
                            org=f{move=80,pass=-1,bal=0.05,type=b},
                            width=3
                        },
                        low=h{pass=10}
                        f{move=80,pass=-1,bal=0.05,type=b},
                        vert=80,
                        rat=0.8
                    }
                )
            },
            pass=5,
            vert=10000,
            rat=0.8
        },
        seq=r
        {
            job=t,
            bal=0.05,
            map=t,
            poli=S,
            sep=
            (
                m
                {
                    asc=b
                    {
                        bnd=(d{pass=40,type=b}|)
                        f{move=80,pass=-1,bal=0.05,type=b},
                        org=f{move=80,pass=-1,bal=0.05,type=b},
                        width=3
                    },
                    low=h{pass=10}
                    f{move=80,pass=-1,bal=0.05,type=b},
                    vert=80,
                    rat=0.8
                }
               |m
                {
                    asc=b
                    {
                        bnd=(d{pass=40,type=b}|)
                        f{move=80,pass=-1,bal=0.05,type=b},
                        org=f{move=80,pass=-1,bal=0.05,type=b},
                        width=3
                    },
                    low=h{pass=10}
                    f{move=80,pass=-1,bal=0.05,type=b},
                    vert=80,
                    rat=0.8
                }
            )
        },
        bal=0.05
    }
 
    Note: writeGraph=true : writes out .dgr files for debugging. Run with e.g.
 
        mpirun -np 4 dgpart 2 'region0_%r.dgr'
 
    - %r gets replaced by current processor rank
    - decompose into 2 domains
 
\*---------------------------------------------------------------------------*/
 
#include "ptscotchDecomp.H"
#include "addToRunTimeSelectionTable.H"
#include "Time.H"
#include "OFstream.H"
#include "globalIndex.H"
#include "SubField.H"
 
extern "C"
{
    #include <stdio.h>
    #include <mpi.h>
    #include "ptscotch.h"
}
 
 
// Hack: scotch generates floating point errors so need to switch of error
//       trapping!
#ifdef __GLIBC__
#   ifndef _GNU_SOURCE
#       define _GNU_SOURCE
#   endif
#   include <fenv.h>
#endif
 
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
namespace Foam
{
    defineTypeNameAndDebug(ptscotchDecomp, 0);
 
    addToRunTimeSelectionTable(decompositionMethod, ptscotchDecomp, dictionary);
}
 
// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
void Foam::ptscotchDecomp::check(const int retVal, const char* str)
{
    if (retVal)
    {
        FatalErrorInFunction
            << "Call to scotch routine " << str << " failed."
            << exit(FatalError);
    }
}
 
 
//Foam::label Foam::ptscotchDecomp::decomposeZeroDomains
//(
//    const fileName& meshPath,
//    const List<label>& initadjncy,
//    const List<label>& initxadj,
//    const scalarField& initcWeights,
//
//    List<label>& finalDecomp
//) const
//{
//    globalIndex globalCells(initxadj.size()-1);
//
//    bool hasZeroDomain = false;
//    for (label procI = 0; procI < Pstream::nProcs(); procI++)
//    {
//        if (globalCells.localSize(procI) == 0)
//        {
//            hasZeroDomain = true;
//            break;
//        }
//    }
//
//    if (!hasZeroDomain)
//    {
//        return decompose
//        (
//            meshPath,
//            initadjncy,
//            initxadj,
//            initcWeights,
//            finalDecomp
//        );
//    }
//
//
//    if (debug)
//    {
//        Info<< "ptscotchDecomp : have graphs with locally 0 cells."
//            << " trickling down." << endl;
//    }
//
//    // Make sure every domain has at least one cell
//    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
//    // (scotch does not like zero sized domains)
//    // Trickle cells from processors that have them up to those that
//    // don't.
//
//
//    // Number of cells to send to the next processor
//    // (is same as number of cells next processor has to receive)
//    List<label> nSendCells(Pstream::nProcs(), 0);
//
//    for (label procI = nSendCells.size()-1; procI >=1; procI--)
//    {
//        label nLocalCells = globalCells.localSize(procI);
//        if (nLocalCells-nSendCells[procI] < 1)
//        {
//            nSendCells[procI-1] = nSendCells[procI]-nLocalCells+1;
//        }
//    }
//
//    // First receive (so increasing the sizes of all arrays)
//
//    Field<int> xadj(initxadj);
//    Field<int> adjncy(initadjncy);
//    scalarField cWeights(initcWeights);
//
//    if (Pstream::myProcNo() >= 1 && nSendCells[Pstream::myProcNo()-1] > 0)
//    {
//        // Receive cells from previous processor
//        IPstream fromPrevProc(Pstream::blocking, Pstream::myProcNo()-1);
//
//        Field<int> prevXadj(fromPrevProc);
//        Field<int> prevAdjncy(fromPrevProc);
//        scalarField prevCellWeights(fromPrevProc);
//
//        if (prevXadj.size() != nSendCells[Pstream::myProcNo()-1])
//        {
//            FatalErrorInFunction
//                << "Expected from processor " << Pstream::myProcNo()-1
//                << " connectivity for " << nSendCells[Pstream::myProcNo()-1]
//                << " nCells but only received " << prevXadj.size()
//                << abort(FatalError);
//        }
//
//        // Insert adjncy
//        prepend(prevAdjncy, adjncy);
//        // Adapt offsets and prepend xadj
//        xadj += prevAdjncy.size();
//        prepend(prevXadj, xadj);
//        // Weights
//        prepend(prevCellWeights, cWeights);
//    }
//
//
//    // Send to my next processor
//
//    if (nSendCells[Pstream::myProcNo()] > 0)
//    {
//        // Send cells to next processor
//        OPstream toNextProc(Pstream::blocking, Pstream::myProcNo()+1);
//
//        label nCells = nSendCells[Pstream::myProcNo()];
//        label startCell = xadj.size()-1 - nCells;
//        label startFace = xadj[startCell];
//        label nFaces = adjncy.size()-startFace;
//
//        // Send for all cell data: last nCells elements
//        // Send for all face data: last nFaces elements
//        toNextProc
//            << Field<int>::subField(xadj, nCells, startCell)-startFace
//            << Field<int>::subField(adjncy, nFaces, startFace)
//            <<
//            (
//                cWeights.size()
//              ? static_cast<const scalarField&>
//                (
//                    scalarField::subField(cWeights, nCells, startCell)
//                )
//              : scalarField(0)
//            );
//
//        // Remove data that has been sent
//        if (cWeights.size())
//        {
//            cWeights.setSize(cWeights.size()-nCells);
//        }
//        adjncy.setSize(adjncy.size()-nFaces);
//        xadj.setSize(xadj.size() - nCells);
//    }
//
//
//    // Do decomposition as normal. Sets finalDecomp.
//    label result = decompose(meshPath, adjncy, xadj, cWeights, finalDecomp);
//
//
//    if (debug)
//    {
//        Info<< "ptscotchDecomp : have graphs with locally 0 cells."
//            << " trickling up." << endl;
//    }
//
//
//    // If we sent cells across make sure we undo it
//    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
//
//    // Receive back from next processor if I sent something
//    if (nSendCells[Pstream::myProcNo()] > 0)
//    {
//        IPstream fromNextProc(Pstream::blocking, Pstream::myProcNo()+1);
//
//        List<label> nextFinalDecomp(fromNextProc);
//
//        if (nextFinalDecomp.size() != nSendCells[Pstream::myProcNo()])
//        {
//            FatalErrorInFunction
//                << "Expected from processor " << Pstream::myProcNo()+1
//                << " decomposition for " << nSendCells[Pstream::myProcNo()]
//                << " nCells but only received " << nextFinalDecomp.size()
//                << abort(FatalError);
//        }
//
//        append(nextFinalDecomp, finalDecomp);
//    }
//
//    // Send back to previous processor.
//    if (Pstream::myProcNo() >= 1 && nSendCells[Pstream::myProcNo()-1] > 0)
//    {
//        OPstream toPrevProc(Pstream::blocking, Pstream::myProcNo()-1);
//
//        label nToPrevious = nSendCells[Pstream::myProcNo()-1];
//
//        toPrevProc <<
//            SubList<label>
//            (
//                finalDecomp,
//                nToPrevious,
//                finalDecomp.size()-nToPrevious
//            );
//
//        // Remove locally what has been sent
//        finalDecomp.setSize(finalDecomp.size()-nToPrevious);
//    }
//    return result;
//}
 
 
// Call scotch with options from dictionary.
Foam::label Foam::ptscotchDecomp::decompose
(
    const fileName& meshPath,
    const List<label>& adjncy,
    const List<label>& xadj,
    const scalarField& cWeights,
    List<label>& finalDecomp
) const
{
    List<label> dummyAdjncy(1);
    List<label> dummyXadj(1);
    dummyXadj[0] = 0;
 
    return decompose
    (
        meshPath,
        adjncy.size(),
        (adjncy.size() ? adjncy.begin() : dummyAdjncy.begin()),
        xadj.size(),
        (xadj.size() ? xadj.begin() : dummyXadj.begin()),
        cWeights,
        finalDecomp
    );
}
 
 
// Call scotch with options from dictionary.
Foam::label Foam::ptscotchDecomp::decompose
(
    const fileName& meshPath,
    const label adjncySize,
    const label adjncy[],
    const label xadjSize,
    const label xadj[],
    const scalarField& cWeights,
 
    List<label>& finalDecomp
) const
{
    if (debug)
    {
        Pout<< "ptscotchDecomp : entering with xadj:" << xadjSize << endl;
    }
 
    // Dump graph
    if (decompositionDict_.found("scotchCoeffs"))
    {
        const dictionary& scotchCoeffs =
            decompositionDict_.subDict("scotchCoeffs");
 
        if (scotchCoeffs.lookupOrDefault("writeGraph", false))
        {
            OFstream str
            (
               meshPath + "_" + Foam::name(Pstream::myProcNo()) + ".dgr"
            );
 
            Pout<< "Dumping Scotch graph file to " << str.name() << endl
                << "Use this in combination with dgpart." << endl;
 
            globalIndex globalCells(xadjSize-1);
 
            // Distributed graph file (.grf)
            label version = 2;
            str << version << nl;
            // Number of files (procglbnbr)
            str << Pstream::nProcs();
            // My file number (procloc)
            str << ' ' << Pstream::myProcNo() << nl;
 
            // Total number of vertices (vertglbnbr)
            str << globalCells.size();
            // Total number of connections (edgeglbnbr)
            str << ' ' << returnReduce(xadj[xadjSize-1], sumOp<label>())
                << nl;
            // Local number of vertices (vertlocnbr)
            str << xadjSize-1;
            // Local number of connections (edgelocnbr)
            str << ' ' << xadj[xadjSize-1] << nl;
            // Numbering starts from 0
            label baseval = 0;
            // 100*hasVertlabels+10*hasEdgeWeights+1*hasVertWeighs
            str << baseval << ' ' << "000" << nl;
            for (label cellI = 0; cellI < xadjSize-1; cellI++)
            {
                label start = xadj[cellI];
                label end = xadj[cellI+1];
                str << end-start;
 
                for (label i = start; i < end; i++)
                {
                    str << ' ' << adjncy[i];
                }
                str << nl;
            }
        }
    }
 
    // Strategy
    // ~~~~~~~~
 
    // Default.
    SCOTCH_Strat stradat;
    check(SCOTCH_stratInit(&stradat), "SCOTCH_stratInit");
 
    if (decompositionDict_.found("scotchCoeffs"))
    {
        const dictionary& scotchCoeffs =
            decompositionDict_.subDict("scotchCoeffs");
 
 
        string strategy;
        if (scotchCoeffs.readIfPresent("strategy", strategy))
        {
            if (debug)
            {
                Info<< "ptscotchDecomp : Using strategy " << strategy << endl;
            }
            SCOTCH_stratDgraphMap(&stradat, strategy.c_str());
            //fprintf(stdout, "S\tStrat=");
            //SCOTCH_stratSave(&stradat, stdout);
            //fprintf(stdout, "\n");
        }
    }
 
 
    // Graph
    // ~~~~~
 
    List<label> velotab;
 
 
    // Check for externally provided cellweights and if so initialise weights
 
    scalar minWeights = gMin(cWeights);
    scalar maxWeights = gMax(cWeights);
 
    if (maxWeights > minWeights)
    {
        if (minWeights <= 0)
        {
            WarningInFunction
                << "Illegal minimum weight " << minWeights
                << endl;
        }
 
        if (cWeights.size() != xadjSize-1)
        {
            FatalErrorInFunction
                << "Number of cell weights " << cWeights.size()
                << " does not equal number of cells " << xadjSize-1
                << exit(FatalError);
        }
    }
 
    scalar velotabSum = gSum(cWeights)/minWeights;
 
    scalar rangeScale(1.0);
 
    if (Pstream::master())
    {
        if (velotabSum > scalar(labelMax - 1))
        {
            // 0.9 factor of safety to avoid floating point round-off in
            // rangeScale tipping the subsequent sum over the integer limit.
            rangeScale = 0.9*scalar(labelMax - 1)/velotabSum;
 
            WarningInFunction
                << "Sum of weights has overflowed integer: " << velotabSum
                << ", compressing weight scale by a factor of " << rangeScale
                << endl;
        }
    }
 
    Pstream::scatter(rangeScale);
 
    if (maxWeights > minWeights)
    {
        if (cWeights.size())
        {
            // Convert to integers.
            velotab.setSize(cWeights.size());
 
            forAll(velotab, i)
            {
                velotab[i] = int((cWeights[i]/minWeights - 1)*rangeScale) + 1;
            }
        }
        else
        {
            // Locally zero cells but not globally. Make sure we have
            // some size so .begin() does not return null pointer. Data
            // itself is never used.
            velotab.setSize(1);
            velotab[0] = 1;
        }
    }
 
 
 
    if (debug)
    {
        Pout<< "SCOTCH_dgraphInit" << endl;
    }
    SCOTCH_Dgraph grafdat;
    check(SCOTCH_dgraphInit(&grafdat, MPI_COMM_WORLD), "SCOTCH_dgraphInit");
 
 
    if (debug)
    {
        Pout<< "SCOTCH_dgraphBuild with:" << nl
            << "xadjSize-1      : " << xadjSize-1 << nl
            << "xadj            : " << uintptr_t(xadj) << nl
            << "velotab         : " << uintptr_t(velotab.begin()) << nl
            << "adjncySize      : " << adjncySize << nl
            << "adjncy          : " << uintptr_t(adjncy) << nl
            << endl;
    }
 
    check
    (
        SCOTCH_dgraphBuild
        (
            &grafdat,               // grafdat
            0,                      // baseval, c-style numbering
            xadjSize-1,             // vertlocnbr, nCells
            xadjSize-1,             // vertlocmax
            const_cast<SCOTCH_Num*>(xadj),
                                    // vertloctab, start index per cell into
                                    // adjncy
            const_cast<SCOTCH_Num*>(xadj+1),// vendloctab, end index  ,,
 
            const_cast<SCOTCH_Num*>(velotab.begin()),// veloloctab, vtx weights
            NULL,                   // vlblloctab
 
            adjncySize,             // edgelocnbr, number of arcs
            adjncySize,             // edgelocsiz
            const_cast<SCOTCH_Num*>(adjncy),         // edgeloctab
            NULL,                   // edgegsttab
            NULL                    // edlotab, edge weights
        ),
        "SCOTCH_dgraphBuild"
    );
 
 
    if (debug)
    {
        Pout<< "SCOTCH_dgraphCheck" << endl;
    }
    check(SCOTCH_dgraphCheck(&grafdat), "SCOTCH_dgraphCheck");
 
 
    // Architecture
    // ~~~~~~~~~~~~
    // (fully connected network topology since using switch)
 
    if (debug)
    {
        Pout<< "SCOTCH_archInit" << endl;
    }
    SCOTCH_Arch archdat;
    check(SCOTCH_archInit(&archdat), "SCOTCH_archInit");
 
    List<label> processorWeights;
    if (decompositionDict_.found("scotchCoeffs"))
    {
        const dictionary& scotchCoeffs =
            decompositionDict_.subDict("scotchCoeffs");
 
        scotchCoeffs.readIfPresent("processorWeights", processorWeights);
    }
    if (processorWeights.size())
    {
        if (debug)
        {
            Info<< "ptscotchDecomp : Using procesor weights "
                << processorWeights
                << endl;
        }
        check
        (
            SCOTCH_archCmpltw(&archdat, nProcessors_, processorWeights.begin()),
            "SCOTCH_archCmpltw"
        );
    }
    else
    {
        if (debug)
        {
            Pout<< "SCOTCH_archCmplt" << endl;
        }
        check
        (
            SCOTCH_archCmplt(&archdat, nProcessors_),
            "SCOTCH_archCmplt"
        );
    }
 
 
    // Hack:switch off fpu error trapping
#   ifdef  FE_NOMASK_ENV
    int oldExcepts = fedisableexcept
    (
        FE_DIVBYZERO
      | FE_INVALID
      | FE_OVERFLOW
    );
#   endif
 
 
    // Note: always provide allocated storage even if local size 0
    finalDecomp.setSize(max(1, xadjSize-1));
    finalDecomp = 0;
 
    if (debug)
    {
        Pout<< "SCOTCH_dgraphMap" << endl;
    }
    check
    (
        SCOTCH_dgraphMap
        (
            &grafdat,
            &archdat,
            &stradat,           // const SCOTCH_Strat *
            finalDecomp.begin() // parttab
        ),
        "SCOTCH_graphMap"
    );
 
#   ifdef  FE_NOMASK_ENV
    feenableexcept(oldExcepts);
#   endif
 
 
 
    //finalDecomp.setSize(xadjSize-1);
    //check
    //(
    //    SCOTCH_dgraphPart
    //    (
    //        &grafdat,
    //        nProcessors_,       // partnbr
    //        &stradat,           // const SCOTCH_Strat *
    //        finalDecomp.begin() // parttab
    //    ),
    //    "SCOTCH_graphPart"
    //);
 
    if (debug)
    {
        Pout<< "SCOTCH_dgraphExit" << endl;
    }
    // Release storage for graph
    SCOTCH_dgraphExit(&grafdat);
    // Release storage for strategy
    SCOTCH_stratExit(&stradat);
    // Release storage for network topology
    SCOTCH_archExit(&archdat);
 
    return 0;
}
 
 
// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
Foam::ptscotchDecomp::ptscotchDecomp(const dictionary& decompositionDict)
:
    decompositionMethod(decompositionDict)
{}
 
 
// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
Foam::labelList Foam::ptscotchDecomp::decompose
(
    const polyMesh& mesh,
    const pointField& points,
    const scalarField& pointWeights
)
{
    if (points.size() != mesh.nCells())
    {
        FatalErrorInFunction
            << "Can use this decomposition method only for the whole mesh"
            << endl
            << "and supply one coordinate (cellCentre) for every cell." << endl
            << "The number of coordinates " << points.size() << endl
            << "The number of cells in the mesh " << mesh.nCells()
            << exit(FatalError);
    }
 
 
    // Make Metis CSR (Compressed Storage Format) storage
    //   adjncy      : contains neighbours (= edges in graph)
    //   xadj(celli) : start of information in adjncy for celli
 
 
    CompactListList<label> cellCells;
    calcCellCells
    (
        mesh,
        identity(mesh.nCells()),
        mesh.nCells(),
        true,
        cellCells
    );
 
    // Decompose using default weights
    List<label> finalDecomp;
    decompose
    (
        mesh.time().path()/mesh.name(),
        cellCells.m(),
        cellCells.offsets(),
        pointWeights,
        finalDecomp
    );
 
    // Copy back to labelList
    labelList decomp(points.size());
    forAll(decomp, i)
    {
        decomp[i] = finalDecomp[i];
    }
    return decomp;
}
 
 
Foam::labelList Foam::ptscotchDecomp::decompose
(
    const polyMesh& mesh,
    const labelList& agglom,
    const pointField& agglomPoints,
    const scalarField& pointWeights
)
{
    if (agglom.size() != mesh.nCells())
    {
        FatalErrorInFunction
            << "Size of cell-to-coarse map " << agglom.size()
            << " differs from number of cells in mesh " << mesh.nCells()
            << exit(FatalError);
    }
 
 
    // Make Metis CSR (Compressed Storage Format) storage
    //   adjncy      : contains neighbours (= edges in graph)
    //   xadj(celli) : start of information in adjncy for celli
    CompactListList<label> cellCells;
    calcCellCells
    (
        mesh,
        agglom,
        agglomPoints.size(),
        true,
        cellCells
    );
 
    // Decompose using weights
    List<label> finalDecomp;
    decompose
    (
        mesh.time().path()/mesh.name(),
        cellCells.m(),
        cellCells.offsets(),
        pointWeights,
        finalDecomp
    );
 
    // Rework back into decomposition for original mesh
    labelList fineDistribution(agglom.size());
 
    forAll(fineDistribution, i)
    {
        fineDistribution[i] = finalDecomp[agglom[i]];
    }
 
    return fineDistribution;
}
 
 
Foam::labelList Foam::ptscotchDecomp::decompose
(
    const labelListList& globalCellCells,
    const pointField& cellCentres,
    const scalarField& cWeights
)
{
    if (cellCentres.size() != globalCellCells.size())
    {
        FatalErrorInFunction
            << "Inconsistent number of cells (" << globalCellCells.size()
            << ") and number of cell centres (" << cellCentres.size()
            << ")." << exit(FatalError);
    }
 
 
    // Make Metis CSR (Compressed Storage Format) storage
    //   adjncy      : contains neighbours (= edges in graph)
    //   xadj(celli) : start of information in adjncy for celli
 
    CompactListList<label> cellCells(globalCellCells);
 
    // Decompose using weights
    List<label> finalDecomp;
    decompose
    (
        "ptscotch",
        cellCells.m(),
        cellCells.offsets(),
        cWeights,
        finalDecomp
    );
 
    // Copy back to labelList
    labelList decomp(cellCentres.size());
    forAll(decomp, i)
    {
        decomp[i] = finalDecomp[i];
    }
    return decomp;
}
 
 
// ************************************************************************* //