Trilinos/Zoltan2: Load Balancing and Combinatorial Scientific Computing.

Contents

• Introduction to Zoltan2
• Overview of the library usage
• Partitioning examples
• Building Zoltan2

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Information specifically for developers can be found at Developers' Notes.

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Introduction to Zoltan2

Zoltan2 is a complete refactoring of the Zoltan library into C++ in order to support template programming, to scale to larger problems, and to support architecture aware partitioning. This library is currently under active development.

Partitioning functionality that is available now is:

• Block partitioning for simple weighted identifiers (really created as a sample algorithm).
• Multi-jagged for weighted geometric coordinates.
• Recursive Coordinate Bisection (RCB) for weighted geometric coordinates.
• Graph partitioning with PTScotch for undirected weighted graphs.

Serial ordering available now is:

• Reverse Cuthill-McKee ordering for RCM ordering.
• Approximate Minimum Degree Ordering for AMD ordering.

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Overview of the library usage

Basic partitioning

Here we describe the typical user interaction with Zoltan2. We use partitioning as an example.

1. Create a Zoltan2::InputAdapter object for your data. This adapter provides a uniform interface to user data for the Zoltan2 library. Adapter interfaces exist for the following classes of data:

• Zoltan2::MatrixInput (a row oriented matrix with optional row weights)
• Zoltan2::GraphInput (an undirected weighted graph)
• Zoltan2::VectorInput (a single or multi-vector with optional weights)
• Zoltan2::CoordinateInput (arbitrary-dimension geometric coordinates)
• Zoltan2::IdentifierInput (simple collection of identifiers)

Zoltan2::MeshInput will be available soon.

2. Create a Teuchos::ParameterList with your Zoltan2 parameters. If you are using a third party library (PT-Scotch, ParMetis) you can include a sublist of parameters for this library. See Zoltan2 Parameters for a detailed list of parameterse.

3. Create a Zoltan2::PartitioningProblem. It is templated on your Zoltan2::InputAdapter type. The constructor arguments are typically your input adapter and your parameter list.

4. Call Zoltan2::PartitioningProblem::solve().

5. Obtain a Zoltan2::PartitioningSolution object from the Zoltan2::PartitioningProblem.

Obtaining partition quality

Repartitioning

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Partitioning examples

Examples include the following:

• Block partitioning (block.cpp)
• RCB partitioning for a C++ novice (rcb_C.cpp)

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Building Zoltan2

Zoltan2 is part of the Trilinos framework and requires several of the other Trilinos libraries to build.

Zoltan2 configuration refers to these CMake directives:

• Trilinos_ENABLE_OpenMP explain
• Trilinos_ENABLE_Zoltan if enabled Zoltan2 will build a test that compares the performance of Zoltan1 and Zoltan2
• Zoltan2_ENABLE_Experimental if enabled, code which is still under development will be available for use
• Explicit Instantiation if explicit instantiation is on, all Zoltan2 tests will be compiled with the instantiated types
• Zoltan2_ENABLE_METIS etc
• Zoltan2_ENABLE_PaToH etc
• Zoltan2_ENABLE_ParMETIS etc
• Zoltan2_ENABLE_Scotch etc
• Zoltan2_ENABLE_OVIS etc
• Zoltan2_ENABLE_AMD etc etc
• Zoltan2_ENABLE_ANASAZI etc

These are some of the compilation flags used by Zoltan2:

• Z2_OMIT_ALL_STATUS_MESSAGES The debug_level parameter controls the verbosity of status messages. When compiled with this option, the checks for debug_level are bypassed and all status output code is ignored.
• Z2_OMIT_ALL_PROFILING Checks are done at runtime to determine whether any of the memory or timer parameters were set, prior to checking memory in use or to start or stop a ttimer. When compiled with this option, those checks are bypassed.
• Z2_OMIT_ALL_ERROR_CHECKING The error_check_level parameter controls the amount of error checking done at runtime. When this flag is set, all error checking code is compiled out.