PARPACK SOFTWARE:

PARPACK (Parallel ARPACK) is an extension of the ARPACK software package 
used for solving large scale eigenvalue problems on distributed memory 
parallel architectures.  The message passing layers currently supported 
are BLACS and MPI.

Routines Availible: 

   - All core ARPACK routines for single, double, complex, and complex16.
   - A small number of example drivers.

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ABOUT ARPACK: 

ARPACK is a collection of Fortran77 subroutines designed to solve large 
scale eigenvalue problems. 

The package is designed to compute a few eigenvalues and corresponding 
eigenvectors of a general n by n matrix A. It is most appropriate for 
large sparse or structured matrices A where structured means that a 
matrix-vector product w <- Av requires order n rather than the usual 
order n**2 floating point operations. This software is based upon an 
algorithmic variant of the Arnoldi process called the Implicitly Restarted 
Arnoldi Method (IRAM). When the matrix A is symmetric it reduces
to a variant of the Lanczos process called the Implicitly Restarted Lanczos 
Method (IRLM). These variants may be viewed as a synthesis of the 
Arnoldi/Lanczos process with the Implicitly Shifted QR technique that is 
suitable for large scale problems. For many standard problems, a matrix
factorization is not required. Only the action of the matrix on a vector is 
needed. 

ARPACK software is capable of solving large scale symmetric, nonsymmetric, 
and generalized eigenproblems from significant application areas. The software 
is designed to compute a few (k) eigenvalues with user specified features such 
as those of largest real part or largest magnitude.  Storage requirements are 
on the order of n*k locations. No auxiliary storage is required. A set of
Schur basis vectors for the desired k-dimensional eigen-space is computed which 
is numerically orthogonal to working precision. Numerically accurate eigenvectors 
are available on request. 

Important Features: 

   -    Reverse Communication Interface. 

   -    Single and Double Precision Real Arithmetic Versions for 
        Symmetric, Non-symmetric, Standard or Generalized Problems. 

   -    Single and Double Precision Complex Arithmetic Versions for 
        Standard or Generalized Problems. 

   -    Routines for Banded Matrices - Standard or Generalized Problems. 

   -    Routines for The Singular Value Decomposition. 

   -    Example driver routines that may be used as templates to implement 
        numerous Shift-Invert strategies for all problem types, data types 
        and precision. 

