LDPC: Python Tools for Low Density Parity Check Codes

2.4.1 verified Fri May 01 auth: no python

A Python library for constructing, encoding, and decoding Low Density Parity Check (LDPC) codes. Current version 2.4.1, active development with periodic releases. Supports a variety of constructions (e.g., random, protograph, QCLDPC) and decoders (belief propagation, min-sum).

pip install ldpc

Common errors

error ModuleNotFoundError: No module named 'ldpc.modules' ↓

cause Package restructured in v2.0; old internal modules no longer exist.

fix

Update imports: from ldpc import LdpcCode, etc. Do not import from ldpc.modules.

error AttributeError: module 'ldpc' has no attribute 'decode' ↓

cause Top-level decode function removed in v2.0.

fix

Use code.decoder().decode(...) or LdpcDecoder.from_code(code).decode(...).

Warnings

breaking In version 2.0+, the internal package structure was refactored. Custom parity-check matrices (H) must be passed as numpy arrays or scipy sparse matrices, not as lists. ↓

fix Ensure H is a 2D numpy array. Use np.array(H_list) if you have a list of lists.

gotcha The decoder's decode() method expects a 1D array of received symbols (0/1 for BSC, or soft bits for AWGN). For soft decoding, set decoder_type='bp' and provide log-likelihood ratios. ↓

fix For BSC: received = (codeword + noise) % 2. For AWGN: received = -2*noisey_llr + 1 (or similar).

deprecated The function `ldpc.decode` (top-level) is deprecated; use `LdpcDecoder.decode` instead. ↓

fix Replace `ldpc.decode(...)` with `decoder.decode(...)` where decoder = code.decoder().

Imports

LDPC code classes
```
from ldpc import LdpcCode, RandomLdpcCode, ProtographLdpcCode, QCLdpcCode
```
Main entry points. Avoid using old module path ldpc.modules.ldpc which was restructured.
Encoder
```
from ldpc import LdpcEncoder
```
Encoder class for linear encoding.
Decoder
```
from ldpc import LdpcDecoder
```
Provides belief propagation (BP) and min-sum decoders.

Utils

from ldpc.utils import hamming_distance, ...

Utility functions moved here.

Quickstart

Basic example: create a random LDPC code, encode, add noise, and decode.

import numpy as np
from ldpc import RandomLdpcCode, LdpcEncoder, LdpcDecoder

# Create a random LDPC code with rate 0.5, block length 100
code = RandomLdpcCode(block_len=100, rate=0.5)

# Encode: generate random message
msg = np.random.randint(0, 2, code.k)
codeword = code.encode(msg)

# Introduce noise (BSC)
noise = np.random.binomial(1, 0.1, codeword.shape)
received = (codeword + noise) % 2

# Decode
decoder = code.decoder()
decoded = decoder.decode(received, max_iter=50)
print('Decoded correctly:', np.array_equal(decoded, codeword))