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Utilities Module

The module implements various utility operations to assist with encoding, decoding and simulations. It includes:

  • Utilities:
    • AList - The class is allows reading and writing "alist" files. "alist" files format which were invented by David MacKay, allow storing sparse matrices efficiently in files. The format is documented here.
    • Frame - Each bit sequence is allocated a frame with a unique id for bookkeeping during simulation.
    • QCFile - This class allows reading and writing qc files which describes quasi cyclical matrices. The format is documented here.

Examples:

AList

from ldpc.utils import AList

# generate an AList object from a file
alist = AList.from_file("code_specs/Mackay_96.3.963.alist")
# convert the object to a standard numpy array
arr = alist.to_array()
# create an instance from an array
foo = AList.from_array(arr)
# save AList to file
foo.to_file("../tests/test_data/test.alist")
# express the matrix as a CodeStructure object
structure = foo.code_params()
# convert AList to a scipy.sparse array
sp = foo.to_sparse()
# or convert a sparse matrix to an AList
bar = AList.from_sparse(sp)

Frames

from ldpc.utils import FramesManager
from bitstring import Bits

# Frames shouldn't be instantiated on their own, but instead using the manager
fm = FramesManager()
# using the manager to crete a frame
bits = Bits(bytes=b"\x01\x02")
tx_frame = fm.create_frame(bits)
# create a copy of the tx_frame to simulate rx
rx_frame = fm.copy_frame(tx_frame)
# Note that copying, copies only bits, ids are still unique
print(rx_frame.uid != tx_frame.uid)
# two frames can be registered as a tx, rx pair:
fm.register_pair(tx_frame, rx_frame)

QCFile

from ldpc.utils import QCFile

# generate an object from a file
qc = QCFile.from_file("../ldpc/code_specs/ieee802.11/N648_R12.qc")
# convert the object to a standard numpy array
arr = qc.to_array()
# create an instance from an existing array
foo = QCFile.from_array(arr, qc.z)
# save object to file
foo.to_file("../tests/test_data/test.qc")
# convert object to a scipy sparse array
sp = foo.to_sparse()
# trying to build an object from an incompatible matrix will raise a value error
arr[1, 2] = 1  # Now the array isn't a column permutation of an identity
QCFile.from_array(arr, qc.z)  # this raises an error