deal.II can interface to the PETSc and Trilinos software libraries. Both of these libraries provide lots of functions for linear algebra, among other things, for example implementations of a variety of linear solvers, as well as various different sparse and dense matrix and vector formats. Trilinos also has many subpackages that deal with problems that go far beyond linear algebra, for example nonlinear solvers, automatic differentiation packages, uncertainty propagation engines, etc. Of particular interest to deal.II is their ability to provide this functionality both on sequential and parallel (using MPI) computers. PETSc is written in C; Trilinos is written in C++ and can be considered to be a more modern version of PETSc though both packages are under continuing development at their respective national laboratories.
deal.II has wrapper classes to the linear algebra parts of both packages that provide almost the same interfaces as the built-in deal.II linear algebra classes. We use these interfaces for parallel computations based on MPI since the native deal.II linear algebra classes lack this ability.
The use of PETSc and Trilinos is optional. To use the wrapper classes,
you first have to install these packages and
point deal.II's ./configure
to the
installation directories. This happens in similar ways for the two
packages:
PETSc usually requires you to set the
environment variables PETSC_DIR
and PETSC_ARCH
to a path to PETSc and denoting the architecture for which PETSc is
compiled. If these environment variables are set, then
deal.II will pick them up during configuration, and
store them. It will then also recognize that PETSc shall be used, and
enable the wrapper classes.
Alternatively, the --with-petsc=DIR
and
--with-petsc-arch=ARCH
switches to
./configure
can be used to override the values
of PETSC_DIR
and PETSC_ARCH
or if these
environment variables are not set at all. If you do have a PETSc installation
and have set the PETSC_DIR
and
PETSC_ARCH
environment variables but do not wish
deal.II to be configured for PETSc use, you
should specify --with-petsc=no
as a flag during
configuration.
Note that in order to use PETSc with deal.II with the current version of deal.II, you need to have at least PETSc version 2.3.1 installed. deal.II version 6.0 has been tested up to PETSc release 2.3.3-p4.
Installing both PETSc and deal.II together can be a bit of a challenge. A good summary of the relevant steps can be found on the Frequently Asked Questions page, as well as in this posting to the mailing list.
As above, set the TRILINOS_DIR
environment variable to the path to an existing Trilinos installation,
or use the --with-trilinos=/path/to/trilinos
switch of
the deal.II ./configure
script. It should point to the path
of which the include and lib directories are subdirs. The Trilinos
installation needs to provide the same kind of libraries that
deal.II is configured for, i.e. if you want deal.II
to use shared libraries, then Trilinos needs to use shared libraries as
well.
deal.II and its tutorial programs use several of the
Trilinos sub-packages. Configuring Trilinos with a command
like the following should do the trick:
../configure --enable-shared \
--with-cflags=-fPIC --with-cxxflags=-fPIC --with-fflags=-fPIC \
--enable-thyra --enable-stratimikos --enable-rtop --enable-teuchos \
--enable-sacado --enable-ml --enable-ifpack --enable-epetra \
--enable-belos --enable-aztecoo --enable-amesos \
--prefix=/home/bangerth/bin/trilinos-9.0.1
The above scheme works if Trilinos is installed in its own directory
and header and library files are in subdirectories of the directory
given to --with-trilinos
. This scheme doesn't work,
however, if Trilinos has been installed as a regular package on a
system, for example into the /usr
or /opt
directories.
In that case, paths to include and library files may be specified
separately using the --with-trilinos-include
and --with-trilinos-libs
switches
to ./configure
. Alternatively, this information can also
be passed to the configuration script by setting the environment
variables TRILINOS_INCDIR, TRILINOS_LIBDIR
.