Deprecation1

Changes to Tpetra's template parameters and offset types

Proposal:

The Tpetra Team proposes the following changes to the templated types and data types used by Tpetra classes.

• Remove template parameters for LocalOrdinal and GlobalOrdinal.

  • LocalOrdinal will be determined during configuration (via CMake options) to be int32_t or int64_t.
  • GlobalOrdinal will be fixed to int64_t.

• Specify the maximum number of nonzeros per MPI rank (sometimes called "offset_type") to be Kokkos::size_type.

• Remove template parameter for Node.

  • Support for various execution spaces (e.g., OpenMP, CUDA) will be determined during configuration via CMake options.
  • When a single execution space is built, Tpetra operations will be done in that execution space by default.
    E.g., Tpetra::MultiVector<scalar_t>::dot(multiVecA, results);
  • New capability to perform heterogeneous operations will be enabled by new interfaces that take execution space as a function parameter, allowing multiple execution spaces to be used.
    E.g., Tpetra::MultiVector<scalar_t>::dot(executionSpaceEnum, multiVecA, results);

Justification:

• Both build times and library size are smaller when fewer template parameters are used and instantiated.
• The Tpetra user interface is simpler with fewer template parameters.
• The Tpetra code base is more maintainable with fewer template parameters.
• Adding the Kokkos ExecutionSpace as an option for Tpetra operations enables heterogeneous computation across multiple execution spaces.

Impact:

• Code changes in applications and other Trilinos packages will likely be simple and straightforward. Most applications already use the proposed local and global ordinal types. When applications have used typedefs to represent Tpetra data types, only the typedefs will need to change.
• Less commonly used combinations of LocalOrdinal and GlobalOrdinal will no longer be supported.

Proposed schedule:

• Conversion path completed and documented in Tpetra: FY18 Q3
• Deprecation warnings for existing templated interface added: FY18 Q3
• Adoption required; deprecated code removed: FY19 Q1

Questions, comments, concerns:

• Please email [email protected] or contact a member of the Tpetra team.

Date: January 30, 2018
SAND2018-1009 O