FFTW3 is a library designed to compute discrete Fourier transforms. As described in the the official FFTW site, there are various versions available, with different features and different levels of maturity. In this tutorial I deal with version 3, including the experimental MPI version. However the installation instructions seems to be valid (although not tested) also for the more popular version 2.
General Remarks
As usual we would like to install the libraries in the user space, so we will create a couple of directories for that purpose:
mkdir $HOME/usr mkdir $HOME/soft
To install FFTW3, download the package from the FFTW3 download page and decompress it:
cd ~/soft wget http://www.fftw.org/fftw-3.3alpha1.tar.gz tar -zxvf fftw-3.3alpha1.tar.gz cd fftw-3.3alpha1
Ubuntu only: If you want to install FFTW3 in your local Ubuntu you can skip this tutorial altogether and just run:
sudo apt-get install libfftw3-dev libfftw3-doc
However the MPI version (e.g. for testing) will not be available. If you want to have the MPI version follow the instructions in the other sections.
Build and Install (serial version only)
Then configure, make and install:
./configure --prefix=$HOME/usr make make install
The following files will be installed in:
~/usr/include/fftw3.h ~/usr/include/fftw3.f ~/usr/lib/libfftw3.a ~/usr/lib/libfftw3.la
The typical compilation options will be
export LD_RUN_PATH=$HOME/usr/lib #do this once *before* compiling cc -I$HOME/usr/include program.c -L$HOME/usr/lib -lfftw3 -o program
The official tutorial on the usage of FFTW3 (which is different from FFTW 2) is located here.
Using LD_RUN_PATH saves us from having to set path variables before *running* the program, such as LD_LIBRARY_PATH (which is a bad practice). When LD_RUN_PATH is set the created executable will store the search path internally (but will not enforce it). I learned this trick from http://gcc.gnu.org/faq.html#rpath and it works well with gcc at least. Setting this variable before compilation can be annoying, but is better than having to set variables *each* time we *use* the executable. This seems to be the only good option left when using libraries installed in the home directory (does anybody know a better alternative?).
Update on LD_RUN_PATH: It seems that the trick of setting this variable does not work with mpicxx, at least with the openmpi implementation. A more general way to store the path of the libraries in the executable seems to be to use the option '-Wl,rpath=$HOME/usr/lib' (sic); as described here.
MPI version
To install the experimental MPI version of FFTW3, make sure you downloaded fftw-3.3alpha1 (and not fftw-3.2 for example). Also make sure that there is an MPI compiler available:
$which mpicc /usr/bin/mpicc
If it is not available, you can choose one with the command 'mpi-selector-menu' in wcr. I tested this with the 'openmpi_gcc-1.2.2' compiler.
Do the same procedure of downloading the file and decompressing it, but add the --enable-mpi flag:
./configure --prefix=$HOME/usr --enable-mpi make install
now the library will be installed in your home directory, besides the files mentioned above, you will find also:
~/usr/include/fftw3-mpi.h ~/usr/lib/libfftw3_mpi.a ~/usr/lib/libfftw3_mpi.la
The typical command line for compilation will be
export LD_RUN_PATH=$HOME/usr/lib #do this *before* compiling mpicc -I$HOME/usr mpi_program.c -L$HOME/usr/lib -lfftw3_mpi -lfftw3 -o mpi_program
Make sure to link *first* to fftw3_mpi and *later* to fftw3. For some MPI platforms (notably openmpi-gcc) setting LD_RUN_PATH does not do the job of storing the library path inside the executables (see not in previous section), it may be necessary to use the following command:
mpicc -Wl,rpath=$HOME/usr/lib -I$HOME/usr mpi_program.c -L$HOME/usr/lib -lfftw3_mpi -lfftw3 -o mpi_program
In any case we should always check that the executable is properly linked by doing
ldd ./mpi_program
and checking that all shared libraries are "found".
The official tutorial for the MPI version of FFTW3 can be found here.