scotchDecomp.H

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Class
    Foam::scotchDecomp
 
Description
    Scotch domain decomposition.
 
    When run in parallel will collect the whole graph on to the master,
    decompose and send back. Use ptscotchDecomp for proper distributed
    decomposition.
 
    Coefficients dictionary: \a scotchCoeffs, \a coeffs.
 
    Quoting from the Scotch forum, on the 2008-08-22 10:09, Francois
    PELLEGRINI posted the following details:
    \verbatim
    RE: Graph mapping 'strategy' string
 
    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 gmap. It is, to date:
 
    r
    {
        job=t,
        map=t,
        poli=S,
        sep=
        (
            m
            {
                asc=b
                {
                    bnd=
                    (
                        d{pass=40,dif=1,rem=1}
                     |
                    )
                    f{move=80,pass=-1,bal=0.002491},
                    org=f{move=80,pass=-1,bal=0.002491},
                    width=3
                },
                low=h{pass=10}
                f{move=80,pass=-1,bal=0.002491},
                type=h,
                vert=80,
                rat=0.8
            }
          | m
            {
                asc=b
                {
                    bnd=
                    (
                        d{pass=40,dif=1,rem=1}
                      |
                    )
                    f{move=80,pass=-1,bal=0.002491},
                    org=f{move=80,pass=-1,bal=0.002491},
                    width=3
                },
                low=h{pass=10}
                f{move=80,pass=-1,bal=0.002491},
                type=h,
                vert=80,
                rat=0.8
            }
        )
    }
    \endverbatim
 
    Given that this information was written in 2008, this example strategy will
    unlikely work as-is with the more recent Scotch versions. Therefore, the
    steps for getting the current default strategy from within Scotch, is to do
    the following steps:
 
    <ol>
    <li> Edit the file <tt>system/decomposeParDict</tt> and use the following
    settings:
 
    \verbatim
    method          scotch;
 
    scotchCoeffs
    {
        writeGraph true;
    }
    \endverbatim
    </li>
 
    <li> Run \c decomposePar. For example, it will write a file named
         <tt>region0.grf</tt>.
    </li>
 
    <li> Now, instead of using \c gmap, run \c gpart with the following
    command structure to get the default strategy:
 
    \verbatim
    gpart <nProcs> -vs <grfFile>
    \endverbatim
 
    where:
 
    <ul>
        <li> <grfFile> is the file that was obtained with the option
             <tt>writeGraph=true</tt>, namely <tt>region0.grf</tt>.
        </li>
        <li> <nProcs> is the \c numberOfSubdomains defined in the dictionary
             file.
        </li>
    </ul>
    </li>
 
    <li> At the end of the execution will be shown a long string, similar to
    the following example (complete line was cropped at <tt>[...]</tt>):
 
    \verbatim
    S    Strat=m{asc=b{width=3,bnd=d{pass=40,dif=1,rem=0}[...],type=h}
    \endverbatim
    </li>
 
    <li> Edit the file <tt>system/decomposeParDict</tt> once again and add
    the \c strategy entry as exemplified:
 
    \verbatim
    method          scotch;
 
    scotchCoeffs
    {
        //writeGraph true;
        strategy "m{asc=b{width=3,bnd=d{pass=40,dif=1,rem=0}[...],type=h}";
    }
    \endverbatim
    </li>
 
    <li> Finally, run \c decomposePar once again, to at least test if it
         works as intended.
    </li>
 
    </ol>
 
Note
    \c gpart can be found in the current search path by adding the respective
    \c bin folder from the Scotch installation, namely by running the following
    commands:
 
    \verbatim
    source $(foamEtcFile config.sh/scotch)
    export PATH=$PATH:$SCOTCH_ARCH_PATH/bin
    \endverbatim
 
SourceFiles
    scotchDecomp.C
 
\*---------------------------------------------------------------------------*/
 
#ifndef scotchDecomp_H
#define scotchDecomp_H
 
#include "metisLikeDecomp.H"
 
namespace Foam
{
 
/*---------------------------------------------------------------------------*\
                           Class scotchDecomp Declaration
\*---------------------------------------------------------------------------*/
 
class scotchDecomp
:
    public metisLikeDecomp
{
    // Private Data
 
        //- Output path and name for optional grf file.
        mutable fileName graphPath_;
 
 
protected:
 
    // Protected Member Functions
 
        //- Decompose non-parallel
        virtual label decomposeSerial
        (
            const labelList& adjncy,
            const labelList& xadj,
            const List<scalar>& cWeights,
            labelList& decomp
        ) const;
 
 
        //- No copy construct
        scotchDecomp(const scotchDecomp&) = delete;
 
        //- No copy assignment
        void operator=(const scotchDecomp&) = delete;
 
 
public:
 
    //- Runtime type information
    TypeName("scotch");
 
 
    // Constructors
 
        //- Construct given decomposition dictionary and optional region name
        explicit scotchDecomp
        (
            const dictionary& decompDict,
            const word& regionName = ""
        );
 
 
    //- Destructor
    virtual ~scotchDecomp() = default;
 
 
    // Member Functions
 
        //- Knows about coupled boundaries
        virtual bool parallelAware() const
        {
            return true;
        }
 
        //- Inherit all decompose methods
        using decompositionMethod::decompose;
 
        //- Return for every coordinate the wanted processor number.
        virtual labelList decompose
        (
            const polyMesh& mesh,
            const pointField& points,
            const scalarField& pointWeights
        ) const;
 
        //- Return for every coordinate the wanted processor number.
        virtual labelList decompose
        (
            const polyMesh& mesh,
            const labelList& agglom,
            const pointField& regionPoints,
            const scalarField& regionWeights
        ) const;
 
        //- Return for every coordinate the wanted processor number.
        virtual labelList decompose
        (
            const labelListList& globalCellCells,
            const pointField& cc,
            const scalarField& cWeights
        ) const;
};
 
 
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} // End namespace Foam
 
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#endif
 
// ************************************************************************* //