## Overview

This is a simple C frontend for ARPACK. This allows easy access to calculating a subset of eigenvectors and eigenvalues of sparse matrices. Specifically it can solve two problems:

- Av = vd
- Av = Mvd

Where A, M are sparse matrices, v is the subset of eigenvectors and d is the diagonal matrix of eigenvalues.

## License

```
Copyright 2010, 2011 Edgar Simo-Serra
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
```

## Installing

To install run:

`# make install`

You will have to be root to install it unless you change the path in the Makefile.

## Documentation

To generate full documentation use the command:

`$ make docs`

Which will generate a pdf containing the full documentation in the directory.

## Changelog

- Version 1.1, January 2012
- Invert the eigenvector/value order to match octave/matlab’s eigs(…) function.
- Support for EIGS_MODE_I_SHIFTINVERT with default driver backend.
- Support for EIGS_MODE_G_SHIFTINVERT with default driver backend.
- Added number of Lanczos vectors to use as a parameter.
- Added driver that uses UMFPACK backend (default).
- Added driver that tries Cholesky factorization, then LU and finally.
- Added driver that tries LU factorization then QR.
- Added driver that tries QR factorization.

- Version 1.0, December 2011
- Initial Revision.
- Support for EIGS_MODE_I_REGULAR with default driver backend.
- Support for EIGS_MODE_G_REGINVERSE with default driver backend.