The ATLAS (Automatically Tuned Linear Algebra Software) project is
an ongoing research effort focusing on applying empirical techniques
in order to provide portable performance. 

At present, it provides C and Fortran77 interfaces to a portable,
efficient BLAS implementation, as well as enhanced versions of 
a few routines from LAPACK.

If you want to link software to ATLAS rather than the standard BLAS, simply 
use -lf77blas -latlas (order is important), or -lptf77blas -latlas for the 
threaded library (which is primarily useful on SMP machines), in place of 
the usual -lblas.  Corresponding pure C versions of the ATLAS libraries are 
also included, in libcblas and libptcblas.

The ATLAS-enhanced LAPACK routines are also provided.
To link software with this library instead of the standard LAPACK, use 
-L/usr/local/lib/gcc-4.2.3 -L/usr/local/lib/gcc-4.2.3/gcc/i386-portbld-freebsd7.0/4.2.3 -lalapack -lf77blas -lcblas -latlas -lgfortranbegin -lgfortran -lm, or 
-L/usr/local/lib/gcc-4.2.3 -L/usr/local/lib/gcc-4.2.3/gcc/i386-portbld-freebsd7.0/4.2.3 -lalapack_r -lptf77blas -lptcblas -latlas -lgfortranbegin -lgfortran
-lm for the threaded library, in place of the usual -llapack.
Note that
-L/usr/local/lib/gcc-4.2.3 -L/usr/local/lib/gcc-4.2.3/gcc/i386-portbld-freebsd7.0/4.2.3
depends on your environment.

WWW: http://math-atlas.sourceforge.net/