Ifpack_LinePartitioner.h

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//       Ifpack: Object-Oriented Algebraic Preconditioner Package
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#ifndef IFPACK_LINEPARTITIONER_H
#define IFPACK_LINEPARTITIONER_H

#include "Ifpack_ConfigDefs.h"
#include "Ifpack_Partitioner.h"
#include "Ifpack_OverlappingPartitioner.h"
#include "Ifpack_Graph_Epetra_RowMatrix.h"
#include "Teuchos_ParameterList.hpp"
class Epetra_Comm;
class Ifpack_Graph;
class Epetra_Map;
class Epetra_BlockMap;
class Epetra_Import;
class Epetra_RowMatrix;

/* \brief Ifpack_LinePartitioner: A class to define partitions into a set of lines.

These "line" partitions could then be used in to do block Gauss-Seidel smoothing, for instance.

The current implementation uses a local (on processor) line detection in one of two forms.
Both are inspired by the work of Mavriplis for convection-diffusion (AIAA Journal, Vol 37(10), 1999).  


Algorithm 1: Matrix entries

Here we use the matrix entries, running lines across the "large" matrix entries, if they are sufficiently
large relative to the small ones.


Algorithms 2: Coordinates

Here we use coordinate information to pick "close" points if they are sufficiently far away
from the "far" points.  We also make sure the line can never double back on itself, so that
the associated sub-matrix could (in theory) be handed off to a fast triangular solver.  This 
implementation doesn't actual do that, however.

This implementation is deived from the related routine in ML.


Supported parameters:
  \c "partitioner: line type": "matrix entries" or "coordinates" (char *)
  \c "partitioner: line detection threshold": if ||x_j - x_i||^2 < thresh * max_k||x_k - x_i||^2, then the points are close enough to line smooth (double)
  \c "partitioner: x-coordinates": x coordinates of local nodes (double *)
  \c "partitioner: y-coordinates": y coordinates of local nodes (double *)
  \c "partitioner: z-coordinates": z coordinates of local nodes (double *)
  \c "partitioner: PDE equations": number of equations per node (integer)

*/

class Ifpack_LinePartitioner : public Ifpack_OverlappingPartitioner {

public:
  // Useful typedef
  typedef enum {COORDINATES=0, MATRIX_ENTRIES,} LINE_MODE;


  Ifpack_LinePartitioner(const Ifpack_Graph* Graph) :
  Ifpack_OverlappingPartitioner(Graph),
    Matrix_(0),
    mode_(COORDINATES),
    NumEqns_(1),
    xcoord_(0),
    ycoord_(0),
    zcoord_(0),
    threshold_(0.0)    
  {
    
  }

 Ifpack_LinePartitioner(const Epetra_RowMatrix* Matrix) :
  Ifpack_OverlappingPartitioner(0),
    Matrix_(Matrix),
    mode_(COORDINATES),
    NumEqns_(1),
    xcoord_(0),
    ycoord_(0),
    zcoord_(0),
    threshold_(0.0)    
  {    
    GraphWrapper_ = Teuchos::rcp(new Ifpack_Graph_Epetra_RowMatrix(Teuchos::rcp(Matrix,false)));
    Graph_ = &*GraphWrapper_;
        
  }


  virtual ~Ifpack_LinePartitioner() {}

  int SetPartitionParameters(Teuchos::ParameterList& List)
  {
    std::string mymode;
    mode_=COORDINATES;
    mymode = List.get("partitioner: line mode",mymode);
    if(mymode=="coordinates")         mode_=COORDINATES;
    else if(mymode=="matrix entries") mode_=MATRIX_ENTRIES;

    threshold_ = List.get("partitioner: line detection threshold",threshold_);
    if(threshold_ < 0.0)  IFPACK_CHK_ERR(-1);
    if(mode_==COORDINATES && threshold_ > 1.0)  IFPACK_CHK_ERR(-1);


    NumEqns_   = List.get("partitioner: PDE equations",NumEqns_);
    if(NumEqns_ < 1 )  IFPACK_CHK_ERR(-2);
    
    xcoord_   = List.get("partitioner: x-coordinates",xcoord_);
    ycoord_   = List.get("partitioner: y-coordinates",ycoord_);
    zcoord_   = List.get("partitioner: z-coordinates",zcoord_);
    if(mode_==COORDINATES && !xcoord_ && !ycoord_ && !zcoord_) IFPACK_CHK_ERR(-3);

    return(0);
  }

  int ComputePartitions();

private:

  // Useful functions
  int Compute_Blocks_AutoLine(int * blockIndices) const;
  void local_automatic_line_search(int NumEqns, int * blockIndices, int last, int next, int LineID, double tol, int *itemp, double * dtemp) const;

  // Stuff I allocated
  Teuchos::RCP<const Ifpack_Graph> GraphWrapper_;

  // User data
  const Epetra_RowMatrix* Matrix_;
  LINE_MODE mode_;
  int NumEqns_;
  double * xcoord_;
  double * ycoord_;
  double * zcoord_;
  double threshold_;


  // State data
};

#endif // IFPACK_LINEPARTITIONER_H