Development/FFTW

Description	Content
module load	numlib/mkl
Availability	bwUniCluster_2.0 | BwForCluster_JUSTUS_2
License	Commercial. See EULA.
Citing	n/a
Links	Intel MKL Homepage | FFTW Homepage
Graphical Interface	No

1 Description

The Fastest Fourier Transform in the West (FFTW) is a software library for computing discrete Fourier transforms in one or more dimensions, of arbitrary input size, and of both real and complex data (as well as of even/odd data, i.e. the discrete cosine/sine transforms or DCT/DST). FFTW was developed by Matteo Frigo and Steven G. Johnson at the Massachusetts Institute of Technology.

The Intel Math Kernel Library (Intel MKL) offers FFTW2 (for version 2.x) and FFTW3 (for version 3.x) interfaces to the Intel MKL Fast Fourier Transform and Trigonometric Transform functionality. These interfaces enable applications using FFTW to gain performance with Intel MKL without changing the application source code. Therefore, it is highly recommended to use Intel MKL instead of a separate FFTW installation.

2 Availability

Intel MKL is available on selected bwHPC-Clusters. A complete list of versions currently installed on the bwHPC-Clusters can be obtained from the Cluster Information System (CIS).

In order to check which versions of Intel MKL are installed on the compute cluster, run the following command:

$ module avail numlib/mkl

3 Documentation

Online-Documentation.

The help page of the Intel MKL module provides more version specific information:

$ module help numlib/mkl

After loading the module, the environment variable $MKL_DOC_DIR points to the local documentation folder.

4 Usage

4.1 Loading the module

You can load the default version of Intel MKL with the following command:

$ module load numlib/mkl

The module will try to load all modules it needs to function (e.g., compiler, mpi, ...). If loading the module fails, check if you have already loaded one of those modules, but not in the version required by MKL.

If you wish to load another (older) version of Intel MKL, you can do so using

$ module load numlib/mkl/<version>

with <version> specifying the desired version.

5 Hints for compiling and linking

5.1 FFTW Specific Environments

To see a list of all FFTW environments set by the 'module load'-command use the command 'module display numlib/fftw'.
After having loaded the appropriate module(s), you can use several environment variables to compile and link your application.

$ module display numlib/fftw
-------------------------------------------------------------------
/opt/bwhpc/common/modulefiles/numlib/fftw/3.3.3-impi-4.1.1-intel-13.1:
FTW_VERSION = 3.3.3-impi-4.1.1-intel-13.1 
FFTW_HOME = /opt/bwhpc/common/numlib/fftw/3.3.3-impi-4.1.1-intel-13.1 
FFTW_BIN_DIR = /opt/bwhpc/common/numlib/fftw/3.3.3-impi-4.1.1-intel-13.1/bin 
FFTW_INC_DIR = /opt/bwhpc/common/numlib/fftw/3.3.3-impi-4.1.1-intel-13.1/include 
FFTW_LIB_DIR = /opt/bwhpc/common/numlib/fftw/3.3.3-impi-4.1.1-intel-13.1/lib 
FFTW_STA_DIR = /opt/bwhpc/common/numlib/fftw/3.3.3-impi-4.1.1-intel-13.1/lib 
FFTW_SHA_DIR = (empty)
FFTW_MAN_DIR = /opt/bwhpc/common/numlib/fftw/3.3.3-impi-4.1.1-intel-13.1/share/man 
FFTW_INF_DIR = /opt/bwhpc/common/numlib/fftw/3.3.3-impi-4.1.1-intel-13.1/share/info 
FFTW_DOC_DIR = /opt/bwhpc/common/numlib/fftw/3.3.3-impi-4.1.1-intel-13.1/doc 
FFTW_EXA_DIR = /opt/bwhpc/common/numlib/fftw/3.3.3-impi-4.1.1-intel-13.1/examples 
FFTW_WWW = http://www.fftw.org/ 
PATH = /opt/bwhpc/common/numlib/fftw/3.3.3-impi-4.1.1-intel-13.1/bin:$PATH
MANPATH = /opt/bwhpc/common/numlib/fftw/3.3.3-impi-4.1.1-intel-13.1/share/man:$MANPATH
INFOPATH = /opt/bwhpc/common/numlib/fftw/3.3.3-impi-4.1.1-intel-13.1/share/info:$INFOPATH
LD_LIBRARY_PATH = /opt/bwhpc/common/numlib/fftw/3.3.3-impi-4.1.1-intel-13.1/lib:$LD_LIBRARY_PATH 
[...]

5.2 Compile a Serial Program

 $ gcc example.c -o example -I$FFTW_INC_DIR -L$FFTW_LIB_DIR -lfftw3 -lm

5.2.1 with POSIX Threads

Compile program with support for POSIX threads.

 $ gcc example.c -o example -I$FFTW_INC_DIR -L$FFTW_LIB_DIR -lfftw3_threads -lfftw3 -lpthread -lm

5.3 Compile program with support for OpenMP threads

 $ gcc example.c -o example -fopenmp -I$FFTW_INC_DIR -L$FFTW_LIB_DIR -lfftw3_omp -lfftw3 -lm

5.4 Compile program with support for MPI

 $ mpicc example.c -o example -I$FFTW_INC_DIR -L$FFTW_LIB_DIR -lfftw3_mpi -lfftw3 -lm 

5.4.1 Run program with MPI support

 $ mpirun -n <ncpu> ./example 

(Replace <ncpu> by number of processor cores.)

Replace -lfftw3, -lfftw3_threads, etc. by -lfftw3f, -lfftw3f_threads, etc. for single precision and by -lfftw3l, -lfftw3l_threads etc. for long-double precision codes, respectively.

These commands will compile your program with dynamic fftw library versions in which case you also have to have the fftw module loaded for running the program. Alternatively, you may want to link your program with static fftw library versions. With static fftw libraries it is only necessary to load the fftw module for compiling but not for executing the program.

5.5 Compile program with static fftw library versions

Example for POSIX threads support

 $ gcc example.c -o example -I$FFTW_INC_DIR $FFTW_LIB_DIR/{libfftw3_threads.a,libfftw3.a} -lpthread -lm 

or:

 $ gcc example.c -o example -I$FFTW_INC_DIR -L$FFTW_LIB_DIR -Wl,-Bstatic -lfftw3 -lfftw3_threads \
       -Wl,-Bdynamic -lpthread -lm 

Environment variables $FFTW_INC_DIR, $FFTW_LIB_DIR etc. are available after loading the module.

6 Examples

Sometimes, FFTW is not available on your cluster. You can use the MKL library instead and include the FFTW functions, too. Various examples can be found in $MKLROOT/examples.

If any assistance, please feel free to contact 'compchem [at] bwhpc.de' or submit a trouble ticket at https://www.bwhpc.de/supportportal.

Intel Math Kernel Library (MKL) offers FFTW2 and FFTW3 interfaces to Intel MKL Fast Fourier Transform and Trigonometric Transform functionality. The purpose of these interfaces is to enable applications using FFTW to gain performance with Intel MKL without changing the program source code.
Here is an excerpt from 'module help numlib/mkl':

Static FFTW2/3 C/Fortran interfaces can be found in dir
    ${MKL_HOME}/interfaces/
  Examples:
    Link to FFTW3 Fortran interface with GNU compiler and ilp64 support:
      ${MKL_HOME}/interfaces/fftw3xf/libfftw3xf_intel64_double_i8_gnu47.a
    Link to FFTW3 Fortran interface with Intel compiler and lp64 support:
      ${MKL_HOME}/interfaces/fftw3xf/libfftw3xf_intel64_double_i4_intel150.a
  The Intel FFTW interfaces requires the Intel MKL library (e.g. it does
  not work with ACML library). Usually it is not a problem to use a
  different compiler version, e.g. to use _gnu41.a with gnu 4.3 compiler.
  See dir ${MKL_HOME}/interfaces/ for other interfaces (fftw2/3 Fortran/C).
  Compiler option for include files: -I${MKL_INC_DIR}/fftw

See the corresponding webpages:

• FFTW Interface to Intel Math Kernel Library
• FFTW2 Interface to Intel Math Kernel Library
• FFTW3 Interface to Intel Math Kernel Library

7 Useful links

• Documentation (english)
• Wikipedia article (german)
• Wikipedia article (english)

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