Isorropia: Partitioning and Rebalancing package

Version 3.0d

Introduction

Isorropia is a repartitioning/rebalancing package, intended to assist with redistributing objects such as matrices and matrix-graphs in a parallel execution setting, to allow for more efficient computations. To enable Isorropia in your Trilinos build, provide the argument '--enable-isorropia' to configure.

Isorropia is primarily an interface to the Zoltan library, but can be built and used with minimal capability without Zoltan. To enable Isorropia's Zoltan support, you need to add '--enable-isorropia-zoltan' and '--enable-epetraext' to your Trilinos configure command, and provide include-paths and library specifications for Zoltan version 3.0 or higher (provide these to configure using the '--with-incdirs' and '--with-libs' configure arguments). If you built Zoltan with third party libraries, e.g. ParMETIS, then you must also link with these libraries.

Overview of Isorropia
Example Programs
Defaults, Parameters

Overview of Isorropia.

Isorropia's user interface consists primarily of the Isorropia::Partitioner, Isorropia::Redistributor and Isorropia::CostDescriber classes, as well as the Isorropia::Epetra::create_balanced_copy functions.

The Isorropia::create_balanced_copy functions are free-standing functions (not class members) which simply take an input object (Epetra_CrsGraph, Epetra_CrsMatrix, etc.) and return a copy which is balanced across partitions.

For more sophisticated use-cases, such as performing one partitioning and then using it to redistribute multiple objects, it is more efficient to use the Isorropia::Partitioner and Isorropia::Redistributor classes. The general usage model is to:

create a Isorropia::Partitioner instance (providing as input the matrix-graph or row-matrix object that is to be re-partitioned, and optionally a Isorropia::CostDescriber instance with weights/costs to influence the partitioning).
create a Isorropia::Redistributor object (providing as input a Isorropia::Partitioner instance)
Use the Isorropia::Redistributor to redistribute one or more objects to the new partitioning.

Isorropia is currently aimed primarily at repartitioning/redistributing Epetra objects, including Epetra_CrsGraph, Epetra_RowMatrix (which includes Epetra_CrsMatrix and Epetra_VbrMatrix) and Epetra_MultiVector.

Example Programs

A number of example programs which demonstrate using Isorropia are provided in the 'packages/isorropia/example' subdirectory.

matrix_1.cpp demonstrates creating a balanced copy of Epetra_CrsGraph and Epetra_CrsMatrix objects using Isorropia::Epetra::create_balanced_copy functions.

part_redist.cpp demonstrates repartitioning and redistributing the contents of an Epetra_LinearProblem object, using the Isorropia::Partitioner and Isorropia::Redistributor classes. This program does not use user-specified weights/costs.

Other programs in the example subdirectory demonstrate the use of weights/costs data to influence the partitioner. See vert_weights.cpp, graphedge_weights.cpp and hgedge_weights.cpp.

Defaults, Parameters, ...

Several Isorropia classes and methods accept Teuchos::ParameterList objects, allowing the user to control certain behavior.

Choice of partitioner
If Isorropia is configured with Zoltan support, then by default Zoltan will be used as the partitioner. To use the simple built-in linear partitioner instead, set the following parameter:
```
  Teuchos::ParameterList params;
  params.set("PARTITIONING_METHOD", "SIMPLE_LINEAR");
```
Passing parameters through to Zoltan
Isorropia can relay Zoltan parameters directly to Zoltan. Before passing a Teuchos::ParameterList to Isorropia, create a sublist in it named "Zoltan". Then, any parameters that should be passed to Zoltan itself, can be stored in the sublist exactly as they appear in the Zoltan users guide. Example:
```
  Teuchos::ParameterList params;
  Teuchos::ParameterList& sublist = params.sublist("Zoltan");
  sublist.set("LB_METHOD", "GRAPH");
  sublist.set("PARMETIS_METHOD", "PARTKWAY");
```
Refer to the Zoltan users guide (available at www.cs.sandia.gov/zoltan) for available Zoltan parameters.