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<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></A>

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<LI><UL>
<LI><A NAME="tex2html252"
  HREF="node11.html#SECTION00034010000000000000">2.4.0.1 BLAS and LAPACK</A>
<LI><A NAME="tex2html253"
  HREF="node11.html#SECTION00034020000000000000">2.4.0.2 FFT</A>
<LI><A NAME="tex2html254"
  HREF="node11.html#SECTION00034030000000000000">2.4.0.3 MPI libraries</A>
<LI><A NAME="tex2html255"
  HREF="node11.html#SECTION00034040000000000000">2.4.0.4 Other libraries</A>
<LI><A NAME="tex2html256"
  HREF="node11.html#SECTION00034050000000000000">2.4.0.5 If optimized libraries are not found</A>
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<H2><A NAME="SECTION00034000000000000000"></A>
<A NAME="Sec:Libraries"></A>
<BR>
2.4 Libraries
</H2>

<P>
Q<SMALL>UANTUM </SMALL>ESPRESSO makes use of the following external libraries:

<UL>
<LI>BLAS (<TT>http://www.netlib.org/blas/</TT>) and
</LI>
<LI>LAPACK (<TT>http://www.netlib.org/lapack/</TT>) for linear algebra
</LI>
<LI>FFTW (<TT>http://www.fftw.org/</TT>) for Fast Fourier Transforms
</LI>
</UL>
A copy of the needed routines is provided with the distribution. However,
when available, optimized vendor-specific libraries should be used: this
often yields huge performance gains.

<P>

<H4><A NAME="SECTION00034010000000000000">
2.4.0.1 BLAS and LAPACK</A>
</H4>
Q<SMALL>UANTUM </SMALL>ESPRESSO can use any architecture-optimized BLAS and LAPACK replacements,
like those contained e.g. in the following libraries:
<BLOCKQUOTE>
MKL for Intel CPUs
<BR>
ACML for AMD CPUs
<BR>
ESSL for IBM machines
<BR>
SCSL for SGI Altix
<BR>
SUNperf for Sun

</BLOCKQUOTE>

<P>
If none of these is available, we suggest that you use the optimized ATLAS
library: see 
<BR><TT>http://math-atlas.sourceforge.net/</TT>. Note that ATLAS is not
a complete replacement for LAPACK: it contains all of the BLAS, plus the
LU code, plus the full storage Cholesky code. Follow the instructions in the
ATLAS distributions to produce a full LAPACK replacement.

<P>
Sergei Lisenkov reported success and good performances with optimized
BLAS by Kazushige Goto. The library is now available under an
open-source license: see the GotoBLAS2 page at 
<BR><TT>http://www.tacc.utexas.edu/tacc-software/gotoblas2/</TT>.

<P>

<H4><A NAME="SECTION00034020000000000000">
2.4.0.2 FFT</A>
</H4>
Q<SMALL>UANTUM </SMALL>ESPRESSO has an internal copy of an old FFTW library. It also supports
the newer FFTW3 library and some vendor-specific FFT libraries.
<TT>configure</TT> will first search for vendor-specific FFT libraries;
if none is found, it will search for an external FFTW v.3 library;
if none is found, it will fall back to the internal  copy of FFTW.
<TT>configure</TT> will add the appropriate preprocessing options:

<UL>
<LI><TT>-D__LINUX_ESSL</TT> for ESSL on IBM Linux machines,
</LI>
<LI><TT>-DASL</TT> for NEC ASL library on NEC machines,
</LI>
<LI><TT>-D__ARM_LIB</TT> for ARM Performance library,
</LI>
<LI><TT>-D__DFTI</TT>  for DFTI (Intel MKL library),
</LI>
<LI><TT>-D__FFTW3</TT> for FFTW3 (external),
</LI>
<LI><TT>-D__FFTW</TT>) for FFTW (internal library),
</LI>
</UL>
to <TT>DFLAGS</TT> in the <TT>make.inc</TT> file.
If you edit <TT>make.inc</TT> manually, please note that one and
only one among the mentioned preprocessing option must be set.

<P>
If you have MKL libraries, you may either use the provided FFTW3
interface (v.10 and later), or directly link FFTW3 from MKL (v.12
and later) or use DFTI (recent versions).

<P>

<H4><A NAME="SECTION00034030000000000000">
2.4.0.3 MPI libraries</A>
</H4>
MPI libraries are usually needed for parallel execution
(unless you are happy with OpenMP multicore parallelization).
In well-configured machines, <TT>configure</TT> should find the appropriate
parallel compiler for you, and this should find the appropriate
libraries. Since often this doesn't
happen, especially on PC clusters, see Sec.<A HREF="node14.html#SubSec:LinuxPCMPI">2.7.7</A>.

<P>

<H4><A NAME="SECTION00034040000000000000">
2.4.0.4 Other libraries</A>
</H4>
Q<SMALL>UANTUM </SMALL>ESPRESSO can use the MASS vector math
library from IBM, if available (only on AIX).

<P>

<H4><A NAME="SECTION00034050000000000000">
2.4.0.5 If optimized libraries are not found</A>
</H4>
The <TT>configure</TT> script attempts to find optimized libraries, but may fail
if they have been installed in non-standard places. You should examine
the final value of <TT>BLAS_LIBS, LAPACK_LIBS, FFT_LIBS, MPI_LIBS</TT> (if needed),
<TT>MASS_LIBS</TT> (IBM only), either in the output of <TT>configure</TT> or in the generated
<TT>make.inc</TT>, to check whether it found all the libraries that you intend to use.

<P>
If some library was not found, you can specify a list of directories to search
in the environment variable <TT>LIBDIRS</TT>,
and rerun <TT>configure</TT>; directories in the
list must be separated by spaces. For example:
<PRE>
   ./configure LIBDIRS="/opt/intel/mkl70/lib/32 /usr/lib/math"
</PRE>
If this still fails, you may set some or all of the <TT>*_LIBS</TT> variables manually
and retry. For example:
<PRE>
   ./configure BLAS_LIBS="-L/usr/lib/math -lf77blas -latlas_sse"
</PRE>
Beware that in this case, <TT>configure</TT> will blindly accept the specified value,
and won't do any extra search.

<P>
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<ADDRESS>
Filippo Spiga
2016-10-04
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