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 "Teuchos_ParameterList.hpp"
class Epetra_Comm;
class Ifpack_Graph;
class Epetra_Map;
class Epetra_BlockMap;
class Epetra_Import;

/* \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 line detection inspired by the work of Mavriplis
for convection-diffusion (AIAA Journal, Vol 37(10), 1999).  

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 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:

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

  virtual ~Ifpack_LinePartitioner() {};

  int SetPartitionParameters(Teuchos::ParameterList& List)
  {
    threshold_ = List.get("partitioner: line detection threshold",threshold_);
    if(threshold_ < 0.0 || 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(!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;


  // User data
  int NumEqns_;
  double * xcoord_;
  double * ycoord_;
  double * zcoord_;
  double threshold_;

  // State data
};

#endif // IFPACK_LINEPARTITIONER_H