## Description

A binary linear code with a sparse parity-check matrix. Alternatively, a member of an infinite family of \([n,k,d]\) codes for which the number of nonzero entries in each row and column of the parity-check matrix are both bounded above by a constant as \(n\to\infty\).

An LDPC code is \((j,k)\)-regular if the parity-check matrix has a fixed number of \(j\) nonzero entries in each row and \(k\) entries in each column; otherwise, the LDPC code is irregular. Irregular LDPC codes are characterized by the fractions \(v_j\) of columns of weight \(j\) as well as likewise fractions \(h_j\) for rows of weight \(j\); these are collectively called the degree distribution.

A parity check is performed by taking the inner product of a row of the parity-check matrix with a codeword that has been affected by a noise channel. A parity check yields either zero (no error) or one (error).

In alternative conventions (not used here), LDPC codes are referred to as simple LDPC codes, as opposed to generalized LDPC codes, alternatively named as Tanner codes.

## Rate

## Encoding

## Decoding

## Notes

## Parents

## Children

## Cousins

- Tensor-product code — Tensor products of random LDPC codes are robustly testable [35,36].
- Low-density generator-matrix (LDGM) code — The dual of an LDPC code has a sparse generator matrix and is called an LDGM code.
- Random code — LDPC codes are often constructed non-determinisitically.
- Tornado code — Tornado codes are similar to LDPC codes, but they use a highly irregular weight distribution for the underlying graphs [37].
- Low-rank parity-check (LRPC) code — LRPC codes are rank-metric analogues of LDPC codes [38].
- LDPC convolutional code (LDPC-CC) — LDPC-CCs are convolutional analogues of LDPC codes.
- Quantum low-density parity-check (QLDPC) code

## References

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## Page edit log

- Victor V. Albert (2022-08-17) — most recent
- Victor V. Albert (2022-04-25)
- Armin Gerami (2022-04-23)

## Cite as:

“Low-density parity-check (LDPC) code”, The Error Correction Zoo (V. V. Albert & P. Faist, eds.), 2022. https://errorcorrectionzoo.org/c/ldpc

Github: https://github.com/errorcorrectionzoo/eczoo_data/tree/main/codes/classical/bits/tanner/ldpc.yml.