.. _lapack_install:

=============================================================
Installing LAPACK and BLAS
=============================================================

See :ref:`linalg` for more references.

First see if these are already installed.  You could do this by going to the
directory `$CLASSHG/codes/lapack/random` and typing::

    $ make randomsys3.exe

if you get a message like::

    ld: library not found for -lblas

then you'll need to install these.

This was discussed in Lecture 17.

To install BLAS and LAPACK, see the links below and also:

 * `<http://gcc.gnu.org/wiki/GfortranBuild>`_

On some linux systems, including the VM for the class, you can install both
BLAS and LAPACK via::

    $ sudo apt-get install liblapack-dev 

The BLAS can be installed by downloading from
`<http://www.netlib.org/blas/blas.tgz>`_

Put this in desired location, e.g. $CLASSHG/codes/lapack/blas.tgz
and then::

    $ cd $CLASSHG/codes/lapack
    $ tar -zxf blas.tgz    # creates BLAS subdirectory
    $ cd BLAS
    $ gfortran -O3 -c *.f
    $ ar cr libblas.a *.o  # creates libblas.a


To use this library::

    $ gfortran -lblas -L$CLASSHG/codes/lapack/BLAS  \
               program.f90

A small subset of LAPACK routines are in
$CLASSHG/codes/lapack/lapack-subset.  In this directory do::

    $ make lib

which should create `liblapack.a`.

To use this library::

    $ gfortran -lblas -L$CLASSHG/codes/lapack/BLAS  \
               -llapack -L$CLASSHG/codes/lapack/lapack-subset \
               program.f90

With these you should be able to run the codes in
$CLASSHG/codes/lapack/random, though you may need to add -L flags in the
Makefile if you've put libraries in nonstandard places as in the above
examples.

To get additional LAPACK routines separately, see
`<http://www.netlib.org/lapack/double/>`_ and click on some routine name
plus dependencies to get a zip or tar file of the routine and any other
routines it calls.

Some references:

 * `LAPACK <http://www.netlib.org/lapack/>`_
 * `LAPACK User's Guide <http://www.netlib.org/lapack/lug/>`_
 * :ref:`blas`
 * `Automatically Tuned Linear Algebra Software (ATLAS) <http://math-atlas.sourceforge.net/>`_
 * `<http://en.wikipedia.org/wiki/LAPACK>`_