# Template:Installing BLAS and LAPACK

### From AbInitio

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### BLAS

The first thing you must have on your system is a BLAS implementation. "BLAS" stands for "Basic Linear Algebra Subroutines," and is a standard interface for operations like matrix multiplication. It is designed as a building-block for other linear-algebra applications, and is used both directly by our code and in LAPACK (see below). By using it, we can take advantage of many highly-optimized implementations of these operations that have been written to the BLAS interface. (Note that you will need implementations of BLAS levels 1-3.)

You can find more BLAS information, as well as a basic implementation, on the BLAS Homepage. Once you get things working with the basic BLAS implementation, it might be a good idea to try and find a more optimized BLAS code for your hardware. Vendor-optimized BLAS implementations are available as part of the HP CXML, IBM ESSL, SGI sgimath, and other libraries. Recently, there has also been work on self-optimizing BLAS implementations that can achieve performance competitive with vendor-tuned codes; see the ATLAS homepage. ATLAS works well, but it does take some time to compile.

Note that the generic BLAS does not come with a `Makefile`

; compile it with something like:

mkdir blas && cd blas # the BLAS archive does not create its own directoryget http://www.netlib.org/blas/blas.tgzgunzip blas.tgz tar xf blas.tar f77 -c -O3 *.f # compile all of the .f files to produce .o files ar rv libblas.a *.o # combine the .o files into a library su -c "cp libblas.a /usr/local/lib" # switch to root and install

(Replace `-O3`

with your favorite optimization options. On Linux, I use `g77 -O3 -fomit-frame-pointer -funroll-loops`

, with `-malign-double -mcpu=i686`

on a Pentium II.) Note that MPB looks for the standard BLAS library with `-lblas`

, so the library file should be called `libblas.a`

and reside in a standard directory like `/usr/local/lib`

. (See also below for the `--with-blas=`

option to MPB's *lib*`configure`

script, to manually specify a library location.)

### LAPACK

LAPACK, the Linear Algebra PACKage, is a standard collection of routines, built on BLAS, for more-complicated (dense) linear algebra operations like matrix inversion and diagonalization. You can download LAPACK from the LAPACK Home Page.

Note that our software looks for LAPACK by linking with `-llapack`

. This means that the library must be called `liblapack.a`

and be installed in a standard directory like `/usr/local/lib`

(alternatively, you can specify another directory via the `LDFLAGS`

environment variable as described earlier). (See also below for the `--with-lapack=`

option to our *lib*`configure`

script, to manually specify a library location.)