Software for Low Density Parity Check Codes Radford M. Neal Version of 2006-02-08. 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 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.