.. index:: TRLan, Lanczos; TRLan
.. _TRLan:

TRLan
=====

Description
-----------

TRLan implements the Thick-Restart Lanczos method for solving large symmetric eigenvalue problems.

User instructions
-----------------

TRLan is available for use with both the GNU and Intel.  To use, load the appropriate module.  For example, to use the serial library, run

.. code-block:: bash

    $ module load trlan/201009

and to use the parallel library, run

.. code-block:: bash

    $ module load trlan-mpi/201009

(Note that TRLan seems to be released with date stamps rather than version numbers.)

To use the serial library add '-ltrlan' to your link link; to use the MPI version add '-ltrlan_mpi'.

TRLan is relatively straightforward (but certainly not black-box) to use.  The programmer must supply the routine to multiply the matrix by trial Lanczos vector.  It is therefore necessary to read the documentation thoroughly, which is available at http://crd.lbl.gov/~kewu/trlan/.

TRLan is written in Fortran.  Whilst it is possible to link to TRLan from other languages, it might be easier to use nu-TRLan for C/C++ projects.

Source
------

http://crd.lbl.gov/~kewu/trlan/ and https://codeforge.lbl.gov/projects/trlan/.

License
-------

No obvious license given that I could find.  It seems safe to provide an appropriate citations in any publications arise from using the library.

Admin notes
-----------

Compilation is quite straightforward.  After making the appropriate settings in Make.inc, run

.. code-block:: bash

    $ make lib

to compile the serial version of the library and 

.. code-block:: bash

    $ make plib

to compile the parallel version of the library.  I used the following Make.inc files:

.. code-block:: make

    # gfortran, serial
    FC=gfortran
    F90=gfortran
    FFLAGS=-O3 
    SHELL=/bin/sh

.. code-block:: make

    # ifort, serial
    FC=ifort
    F90=ifort
    FFLAGS=-O3 
    SHELL=/bin/sh

.. code-block:: make

    # ifort/gfortran, mpi
    FC=mpif90
    F90=mpif90
    FFLAGS=-O3 
    SHELL=/bin/sh

Obviously the compiler and MPI modules had to be loaded.

The libraries, libtrlan.a and libtrlan_mpi.a, are compiled in the root directory.  I created the directory structure to fit in with the standard layout by hand.