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Notes on the packaged version of ATLAS

by Quentin Spencer
updated: October 4, 2005

updated by Deji Akingunola
October 15, 2008

updated by Deji Akingunola
June 15, 2011

updated by Frantisek Kluknavsky
Nov 20, 2012

Because ATLAS relies on compile-time optimizations to obtain improved
performance over BLAS and LAPACK, the resulting binaries are closely
tied to the hardware on which they are compiled, and can likely result
in very poor performance on other hardware.  For this reason,
including a package like ATLAS in Fedora requires some compromises.
Optimizing ATLAS for the most modern hardware can result in
significant performance penalties for users using the same package on
older hardware. A binary ATLAS package must perform reasonably well on the
entire range of hardware on which it could potentially be installed.

The result is a set of libraries that will not
necessarily achieve optimal performance on any given hardware but
should still offer significant performance gains over the reference
BLAS and LAPACK libraries on most hardware.  

In addition to the base 32bit build, subpackages are built for SSE, SSE2,
and SSE3 ix86 extensions.

On 64bit x86 systems the default atlas package was built with SSE3
optimization.
  
This packaging allows multiple installation of different atlas sub-packages
at the same time. The alternatives system (read 'man alternatives' for usage)
is used in the -devel subpackages to select the appropriate location for the 
architectural dependent header files.
 
For users who want optimal performance on
particular hardware, custom RPMs can be built from the source package
by setting the RPM macro "enable_native_atlas" to a value of 1. This
can be done from the command line as in the following example:

rpmbuild -D "enable_native_atlas 1" --rebuild atlas-3.8.3-1.src.rpm
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