komm.LempelZivWelchCode

Lempel–Ziv–Welch (LZW) code. It is a lossless data compression algorithm which is variation of the Lempel–Ziv 78 algorithm. For more details, see Say06, Sec. 5.4.2.

Parameters:

• source_cardinality (int) –

  The source cardinality $S$. Must be an integer greater than or equal to $2$.

• target_cardinality (int) –

  The target cardinality $T$. Must be an integer greater than or equal to $2$. Default is $2$ (binary).

Examples:

>>> lzw = komm.LempelZivWelchCode(2)  # Binary source, binary target
>>> lzw = komm.LempelZivWelchCode(3, 4)  # Ternary source, quaternary target

encode

Encodes a sequence of source symbols using the LZW encoding algorithm.

Parameters:

• input (ArrayLike) –

  The sequence of symbols to be encoded. Must be a 1D-array with elements in $[0:S)$ (where $S$ is the source cardinality of the code).

Returns:

• output (NDArray[integer]) –

  The sequence of encoded symbols. It is a 1D-array with elements in $[0:T)$ (where $T$ is the target cardinality of the code).

Examples:

>>> lzw = komm.LempelZivWelchCode(2)
>>> lzw.encode(np.zeros(15, dtype=int))
array([0, 0, 1, 1, 1, 0, 0, 1, 1, 0, 1])

>>> lzw = komm.LempelZivWelchCode(2, 8)
>>> lzw.encode(np.zeros(15, dtype=int))
array([0, 2, 3, 4, 5])

decode

Decodes a sequence of encoded symbols using the LZW decoding algorithm.

Parameters:

• input (ArrayLike) –

  The sequence of symbols to be decoded. Must be a 1D-array with elements in $[0:T)$ (where $T$ is the target cardinality of the code). Also, the sequence must be a valid output of the encode method.

Returns:

• output (NDArray[integer]) –

  The sequence of decoded symbols. It is a 1D-array with elements in $[0:S)$ (where $S$ is the source cardinality of the code).

Examples:

>>> lzw = komm.LempelZivWelchCode(2)
>>> lzw.decode([0, 0, 1, 1, 1, 0, 0, 1, 1, 0, 1])
array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0])

>>> lzw = komm.LempelZivWelchCode(2, 8)
>>> lzw.decode([0, 2, 3, 4, 5])
array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0])