Integration of Trilinos Into The Cactus Code Framework

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1 Integration of Trilinos Into The Cactus Code Framework Josh Abadie Research programmer Center for Computation & Technology Louisiana State University

2 Summary Motivation Objectives The Cactus Code Trilinos Process of Integration Further Work Acknowledgments

3 Motivation If in other science we should arrive at certainty without doubt and truth without error it behooves us to place the foundations of knowledge in mathematics Roger Bacon Mathematics can be used to describe accurately amazingly complex and otherwise incomprehensible things Complex math problems can be solved with computers Scientific Computing Programs which solve these problems can be very complex Software reuse is therefore important in Scientific Computing because of this complexity Frameworks, like Cactus and libraries, like Trilinos facilitate reuse of code, save time, leave less room for error, and encourage cooperation in parallel code development

4 Motivation: Parallel Code Development Parallel computing is an attempt to maximize the infinite but seemingly scarce commodity called time. Traditionally, software has been written for serial computation In the simplest sense, parallel computing is the simultaneous use of multiple compute resources to solve a computational problem Source:

5 Motivation: Parallel Programming Complexity Parallel applications usually much more complex than corresponding serial applications, perhaps an order of magnitude Not only do you have multiple instruction streams executing at the same time, but you also have data flowing between them So complex is parallel programming that frameworks like Cactus exist to make the job easier Source:

6 Objectives Cactus is not the answer to all our prayers: other frameworks exist that contain specialized code (solvers, preconditioners ) that we need to use in order to solve complex problems Since Cactus is extensible, we want to leverage the resource that is Trilinos for use in Cactus The integration of the Trilinos library in Cactus should be seamless, the code should have a clear interface that is easy to use

7 Cactus Code Framework Open source application framework designed primarily for scientists and engineers Simple and easy to extend in both C/C++ and Fortran The Flesh Glue for the framework The Thorns - actual computation Modules of Cactus

8 Structure of Cactus Plug-In Thorns (modules) driver input/output extensible APIs ANSI C CCL Interpreter scheduling Core Flesh remote steering Fortran/C/C++ equations of state interpolation SOR solver error handling parameters grid variables make system black holes boundary conditions wave evolvers multigrid coordinates Source: Tom Goodale

9 Standard Thorns HDF5 Toolkit PETSc Toolkit Web Browser Toolkit CFD Toolkit I/O using HDF5 data format Library of Elliptic equation solvers Web steering of computations Solving problems in CFD

10 Trilinos Set of Libraries solvers, preconditioners vector, matrix and sparse matrix classes with parallel capability Developed at Sandia National labs Easy to use, well documented common set of Data structures - Epetra

11 Trilinos Libraries LAPACK Algebraic preconditioner IFPACK Algebraic preconditioner ML Multilevel preconditioner Aztec Linear Solver NOX Collection of nonlinear solvers Anasazi Collection on eigen solvers Komplex Complex Solver Belos Krylov linear solver

12 Process of Integration Create Trilinos Libraries Documentation concise and very helpful Easy to make multiple builds with different configurations Create a Cactus thorn Create a thorn which tells Cactus about Trilinos and where the libraries are located To use Trilinos, just require the thorn, set some environment variables, write your thorn

13 Using Trilinos In Cactus Plug-In Thorns (module) extensible APIs ANSI C parameters Trilinos-Test scheduling Core Flesh Dependency Checking Trilinos error handling make system grid variables

14 Future Work Utility library A set of functions to simplify the process of using Trilinos in Cactus MPI transparency Data translation Epetra Driver Cactus Thorn which stores all data does all memory management with Trilinos Epetra classes Ultimate integration of Trilinos and Cactus Benchmarking

15 Acknowledgements Yaakoub El Khamra supervisor and mentor, Frameworks at CCT Gabrielle Allen Assistant Director of the Center for Computation and Technology Tom Goodale Chief Architect of the Cactus Code Framework Kathryn Traxler Education and Outreach at CCT The Trilinos Project Team Development of such a great library The Computer Science Department and Louisiana State University Assistance with funding