# 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 Compaq 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 (and also PhiPACK). Links to more BLAS implementations can be found on SAL. I recommend ATLAS, 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. More LAPACK links can be found on SAL.

Note that MPB 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 MPB's *lib*`configure`

script, to manually specify a library location.)