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Ordering Algorithms

The following graph (sparse matrix) ordering algorithms are currently included in the Zoltan toolkit:
Nested dissection by METIS/ParMETIS
Nested dissection by PT-Scotch
These methods produce orderings that reduce fill in sparse matrix factorizations (Cholesky). Ordering is accessed through calls to Zoltan_Order.

Third-party libraries

Currently, all ordering in Zoltan is provided through the third-party libraries METIS/ParMETIS and PT-Scotch. At least one of these must be present to use Zoltan ordering.

Ordering Parameters

While the overall behavior of Zoltan is controlled by general Zoltan parameters, the behavior of each ordering method is controlled by parameters specific to ordering which are also set by calls to Zoltan_Set_Param. Many of these parameters are specific to individual ordering algorithms, and are listed in the descriptions of the individual algorithms.  However, several have meaning across multiple ordering algorithms. These parameters are described below.
 
Parameters:
   ORDER_METHOD The order algorithm used by Zoltan is specified by this parameter. Valid values are 
"NODEND" (for nodal nested dissection by ParMETIS or METIS),
"METIS" (same as NODEND with ORDER_TYPE = local),
"PARMETIS" (same as NODEND with ORDER_TYPE = global),
"SCOTCH", and
"NONE" (for no ordering).
   ORDER_TYPE "LOCAL" or "GLOBAL". If LOCAL is selected, then each processor constructs a local (sub-)graph. All inter-processor edges are simply ignored.  The ordering arrays returned, rank and iperm, are local permutation vectors in this case.
ORDER_START_INDEX The start index for the permutation vectors rank and iperm. Valid values are 0 and 1.
    REORDER If this value is set to TRUE (non-zero), Zoltan assumes that the lists of local and global ids are given as input to Zoltan_Order. Otherwise, the id lists will be populated by Zoltan_Order.  The permutation of the ids will be the one produced by calling the query functions.
Default Values:
ORDER_METHOD = NODEND
ORDER_TYPE = GLOBAL
ORDER_START_INDEX = 0
REORDER = FALSE

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