Micro and Nano Mechanics Group
Revision as of 23:16, 29 January 2009 by Correaa (Talk)

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 also for version 2 (not tested).

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.

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.

The official tutorial for the MPI version of FFTW3 can be found here.