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<LI><A NAME="tex2html255"
  HREF="node11.html#SECTION00034010000000000000">2.4.0.1 BLAS and LAPACK</A>
<LI><A NAME="tex2html256"
  HREF="node11.html#SECTION00034020000000000000">2.4.0.2 FFT</A>
<LI><A NAME="tex2html257"
  HREF="node11.html#SECTION00034030000000000000">2.4.0.3 MPI libraries</A>
<LI><A NAME="tex2html258"
  HREF="node11.html#SECTION00034040000000000000">2.4.0.4 Other libraries</A>
<LI><A NAME="tex2html259"
  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 the following architecture-specific replacements for BLAS and LAPACK:
<BR><BLOCKQUOTE>
MKL for Intel Linux PCs
<BR>
ACML for AMD Linux PCs
<BR>
ESSL for IBM machines
<BR>
SCSL for SGI Altix
<BR>
SUNperf for Sun

</BLOCKQUOTE>
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. They can be freely downloaded,
but not redistributed. See the "GotoBLAS2" item at
<BR><TT>http://www.tacc.utexas.edu/tacc-projects/</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 version, and it 
can use the following vendor-specific FFT libraries:
<BLOCKQUOTE>
IBM ESSL
<BR>
SGI SCSL
<BR>
SUN sunperf
<BR>
NEC ASL

</BLOCKQUOTE>
<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.

<P>
If you have recent versions (v.10 or later) of MKL installed, you 
may use the FFTW3 interface provided with MKL. This can be directly
linked in MKL distributed with v.12 of the Intel compiler. In earlier 
versions, only sources are distributed: you have to compile them and 
to modify file <TT>make.sys</TT> accordingly 
(MKL must be linked <EM>after</EM> the FFTW-MKL interface).

<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">2.7.6</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.sys</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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