# Software for Low Density Parity Check Codes

Version in development.

This collection of programs and modules, written in C, is intended to support research and education concerning Low Density Parity Check (LDPC) codes. (Note, however, that the copyright notice no longer restricts use to these purposes). These error-correcting codes were invented by Robert Gallager in the early 1960's, and re-invented and shown to have very good performance by David MacKay and myself in the mid-1990's. The decoding algorithm for LDPC codes is related to that used for Turbo codes, and to probabilistic inference methods used in other fields. Variations on LDPC and Turbo codes are currently the best practical codes known, in terms of their ability to transmit data at rates approaching channel capacity with very low error probability.

This and past versions of the software are available here, from Radford Neal's web page. The source code for this software is also hosted at Github, where there is a copy of these documentation pages for the latest release. Github also provides facilities for bug reporting and discussion.

## Index to Documentation

Download and installation instructions

> How to get and compile the programs and modules.

Github facilities

> How to get the source repository, report bugs, etc.

Release notes

> A log of changes made in each release of this software.

Software and program usage documentation

> General documentation on the methods implemented, and details of program usage.

Examples of program usage

> Examples using simple Hamming codes, and using more interesting LDPC codes.

How to modify the programs

> Notes on how to add new channel types, new decoding methods, etc.

Module documentation

> Modules used by the programs for modulo-2 matrix operations and random number generation.

References

> Classic and more recent papers on LDPC codes and related topics.

## Copyright and Lack of Warranty

Except as otherwise specified, all of this software and documentation is copyright © 1995-2012 by Radford M. Neal.

Permission is granted for anyone to copy, use, modify, and distribute these programs and accompanying documents for any purpose, provided this copyright notice is retained and prominently displayed, and note is made of any changes made to these programs. These programs and documents are distributed without any warranty, express or implied. As the programs were written for research purposes only, they have not been tested to the degree that would be advisable in any important application. All use of these programs is entirely at the user's own risk.

Some routines in the module rand.c are taken from the GNU C Library, and are copyrighted as described there and in the file LGPL.