Trilinos Hands-on Tutorial

First things first:

• The Trilinos Project relies heavily upon its website (click on logo above).
• For future reference, a lot of information can be found on the Trilinos "Getting Started" page.
• Trilinos has a Tutorial document that you can find here.
• The 2010 Trilinos User Group meeting included a video-recorded tutorial that uses the website. Part 1 is here. Part 2 is here.
• Much of the rest of 2010 TUG is also available by video here.
• A more focused manycore tutorial starts here.

Let's dive in, you have two options:

• WebTrilinos
• WebTrilinos is a scientific portal, a web-based environment to use several Trilinos packages through the web.
• Note: Only packages that Trilinos was configured with can be used through the WebTrilinos interfaces.
• Installed at St. John's University, MN. The following versions of the C++ interface are available (the examples below use the C++ interface):
• Trilinos 10.8, MPI-enabled
• Trilinos 10.8, TBB-enabled
• Trilinos 10.8, CUDA-enabled
• Trilinos development branch (10.7), MPI-enabled
• Trilinos 10.6, MPI-enabled
• Trilinos 10.4, serial
• Trilinos 10.4, MPI-enabled

• In addition to the C++ interfaces, a Matrix Portal interface and a Python interface are also available.
• Access to this site is password protected. Login information will be given during live tutorials as needed.
• Reminder: Use Ctrl+A to highlight all the example code, Ctrl+C to copy it, and Ctrl+V to paste it in the WebTrilinos window.

• Download and build the examples on your machine
1. Download Trilinos
2. Download and install CMake (if not already done).
• The latest CMake release can be downloaded from here.
3. Download and install Clapack (if you don't have LAPACK and BLAS already).
• Get Clapack from here.
• Use CMake to build Clapack.
4. Build and install Trilinos.
• An example script is here.
• You can find other scripts in the Trilinos distribution Trilinos/sample_scripts directory.
• You can also use the CMake gui, or the text-gui ccmake.
5. Get Makefile from here.
• Learn about the Makefile and the Makefile.export system here.
• You can find the Makefile.export.package_name files once you have built and installed Trilinos.
• They will be in the include directory of your installation directory.
• Example: TrilinosInstall/include/Makefile.export.Epetra.
6. Customize the Makefile to your situation (the example Makefile uses only the Epetra package, but Makefile.export.package_name files are available for all packages).
7. Add Example code into a file called main.cpp and build away!

Now for some examples:

1. Start with some tools using the Teuchos package.
• Basic Support Tools
• Build a parameter list (used to pass parameters to all Trilinos packages).
• Build a reference-counted pointer (used to eliminate memory leak issues in most Trilinos packages).
• Build a command-line parser (tool for changing runtime behavior of program, providing documentation for options). [unhighlighted]
• Build a time monitor (tool for timing individual methods or operations in a program).
• Template Support Tools
• Create a templated BLAS wrapper.
• Create a templated LAPACK wrapper.
• Create a templated serial, dense matrix.
2. Write a program using the Epetra package.
• Beginner: Construct some vectors and perform basic operations.
• Intermediate: Find the dominant eigenpair of a matrix using the power method.
3. Generate a linear system using the Galeri package.
• Generate a matrix, discretized 2D Laplacian on a Cartesian grid.
• Try generating matrices for some different operators, the list of supported operators is here.
4. Create an algebraic preconditioner using the Ifpack package.
• Create a preconditioner using the Ifpack preconditioner factory.
• Try generating different preconditioners:
• The preconditioners supported in the factory interface are: "IC", "ICT", "ILU", "ILUT", and "Amesos".
• The list of supported parameters for the factory is here.
5. Solve a linear system using the Ifpack and AztecOO packages.
• Solve a linear system _Ax=b_ using Ifpack and AztecOO
6. Solve a linear system using the ML and AztecOO packages.
• Solve a linear system _Ax=b_ using ML(black-box) and AztecOO
• Solve a linear system _Ax=b_ using ML and AztecOO, but setting some multigrid options
7. Solve a linear system using the Ifpack and Belos packages.
• Solve a linear system _Ax=b_ using Ifpack and Belos
8. Compute some eigenpairs using the Anasazi package.
• Compute the smallest eigenpairs of a discretized 2D Laplacian using the block Davidson solver.
• Compute the smallest eigenpairs of a discretized 2D Laplacian using the LOBPCG solver.
• Compute the dominant singular values of a 2D discretization of a simple kernel using the block Krylov-Schur solver.
9. Solve a nonlinear system using the NOX package.
• Solve a simple nonlinear system using NOX
• Solve a simple nonlinear system using NOX
10. Tpetra is the new manycore-aware linear algebra stack.
• Basic application initialization for the Tpetra stack
• Basic creation and manipulation of Tpetra vectors
11. PyTrilinos tutorial materials.
• PyTrilinos tutorial slides
• Solve a simple 2D Laplace problem using PyTrilinos

Other examples

Some examples don't work with the web tutorial, since they read from files. You can try them out by downloading Trilinos and looking in the examples in the source tree. For example, the Intrepid discretizations package has examples in the packages/trilinoscouplings/examples/scaling/ directory. The following might be of interest:

• example_CurlLSFEM.cpp: driver for solving div-curl first order system in 3D with tangential boundary condition using curl-conforming elements
• example_DivLSFEM.cpp: driver for the same system with normal boundary condition and div-conforming elements
• example_Poisson.cpp: solving the Poisson equation using a Galerkin finite element method

For Belos' Recycling GMRES (GCRODR) solver, there are examples in packages/belos/epetra/example/GCRODR/PrecGCRODREpetraExFile.cpp and GCRODREpetraExFile.cpp. These examples use the sherman5.hb matrix, which is included in the /packages/belos/epetra/example/GCRODR directory with the Trilinos distribution.

Learning more:

• Online reference documentation.
• Trilinos User Group Meeting (2010).
• Trilinos User Group Meeting (2009).
• Trilinos User Group Meeting (2008).
• Trilinos User Group Meeting (2007).
• Mail lists.