Pure abstract class for unstructured LDPC matrices. More...
#include <itpp/comm/ldpc.h>
Public Member Functions | |
virtual void | display_stats () const =0 |
Display some information about the matrix. | |
int | cycle_removal_MGW (int L) |
Remove cycles (loops) from unstructured parity check matrix. | |
void | initialize (int ncheck, int nvar) |
Initialize an empty matrix of size ncheck x nvar. | |
GF2mat_sparse | get_H (bool transpose=false) const |
Get the parity check matrix, optionally its transposed form. | |
Sparse_Vec< bin > | get_col (int c) const |
Get a specific column from the matrix. | |
Sparse_Vec< bin > | get_row (int r) const |
Get a specific row from the matrix. | |
int | get_nvar () const |
Get the number of variable nodes (number of columns) | |
int | get_ncheck () const |
Get the number of check nodes (number of rows) | |
void | set (int i, int j, bin value) |
Set element (i,j) of the parity check matrix to value. | |
bin | get (int i, int j) const |
Get element (i,j) of the parity check matrix. | |
bin | operator() (int i, int j) const |
Get element (i,j) of the parity check matrix. | |
double | get_rate () const |
Get the code rate. | |
void | import_alist (const GF2mat_sparse_alist &H_alist) |
Import matrix from GF2mat_sparse_alist format. | |
GF2mat_sparse_alist | export_alist () const |
Export matrix to GF2mat_sparse_alist format. | |
void | load_alist (const std::string &alist_file) |
Load matrix from alist_file text file in alist format. | |
void | save_alist (const std::string &alist_file) const |
Save matrix to alist_file text file in alist format. | |
Protected Member Functions | |
void | generate_random_H (const ivec &C, const ivec &R, const ivec &cycopt) |
Generate a random parity check matrix. | |
void | compute_CR (const vec &var_deg, const vec &chk_deg, const int Nvar, ivec &C, ivec &R) |
Compute target number of columns (C) and rows (R) with a specific number of ones. | |
int | check_for_cycles (int L) const |
Check for cycles of length L. | |
int | check_connectivity (int from_m, int from_n, int to_m, int to_n, int g, int L) const |
Check for connectivity between nodes. | |
Protected Attributes | |
bool | init_flag |
Flag that indicates proper initialization. | |
GF2mat_sparse | H |
The parity check matrix. | |
GF2mat_sparse | Ht |
The transposed parity check matrix. | |
int | nvar |
Number of variable nodes. | |
int | ncheck |
Number of check nodes. | |
ivec | sumX1 |
Actual number of ones in each column. | |
ivec | sumX2 |
Actual number of ones in each row. | |
Static Protected Attributes | |
static const int | Nmax = 200 |
Maximum node degree class can handle. | |
Pure abstract class for unstructured LDPC matrices.
This class provides a common set of methods for unstructured LDPC matrices. For unstructured codes the parity checks are distributed at random rather than according to a specific pattern, and the generation of a parity matrix can be viewed as drawing a random sample from an ensemble of graphs (matrices) that are described by a specific degree distribution.
This class is used as base for the LDPC_Parity_Irregular
and LDPC_Parity_Regular
generator classes.
int itpp::LDPC_Parity_Unstructured::cycle_removal_MGW | ( | int | L | ) |
Remove cycles (loops) from unstructured parity check matrix.
This function implements the cycle removal algorithm presented by McGowan and Williamson at the IT workshop 2003. The maximum girth of the graph that will be attempted is L. The algorithm is bound to remove all loops of length L, insofar this is possible. I.e., it does not terminate until it is impossible to remove more cycles by swapping two edges.
L | Target girth. For example, L=6 attempts to removes all 4-cycles. |
Definition at line 292 of file ldpc.cpp.
References itpp::elem_mult(), itpp::floor_i(), itpp::LDPC_Parity::get_col(), itpp::Sparse_Vec< T >::get_nz_index(), itpp::LDPC_Parity::init_flag, it_assert, it_assert_debug, it_info_debug, itpp::length(), itpp::LDPC_Parity::ncheck, itpp::Sparse_Vec< T >::nnz(), itpp::LDPC_Parity::nvar, itpp::randi(), itpp::randu(), and itpp::Array< T >::set_size().
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protected |
Compute target number of columns (C) and rows (R) with a specific number of ones.
var_deg | vector of variable degree distributions, from an edge perspective |
chk_deg | vector of check degree distributions, from an edge perspective |
Nvar | number of variable nodes |
C | number of columns with a specific number of ones |
R | number of rows with a specific number of ones |
The result is passed by reference and saved in C and R.
Definition at line 598 of file ldpc.cpp.
References itpp::concat(), itpp::elem_div(), itpp::elem_mult(), itpp::find(), it_info_debug, itpp::length(), itpp::linspace(), itpp::max(), itpp::LDPC_Parity::Nmax, itpp::round(), itpp::sum(), itpp::to_ivec(), itpp::to_vec(), and itpp::zeros_i().
Referenced by itpp::LDPC_Parity_Irregular::generate(), and itpp::LDPC_Parity_Regular::generate().
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protectedinherited |
Check for cycles of length L.
This function implements a recursive routine to find loops. The function is mainly a tool for testing and debugging more sophisticated functions for graph manipulation.
L | length of cycles to look for |
Definition at line 249 of file ldpc.cpp.
References itpp::LDPC_Parity::check_connectivity(), itpp::LDPC_Parity::get_col(), itpp::Sparse_Vec< T >::get_nz_indices(), itpp::LDPC_Parity::init_flag, it_assert, itpp::length(), and itpp::LDPC_Parity::nvar.
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protectedinherited |
Check for connectivity between nodes.
This function examines whether the point (to_m, to_n) in the matrix can be reached from the point (from_m, from_n) using at most L steps. A recursive search is used.
The function can be used to search for cycles in the matrix. To search for a cycle of length L, set from_m=to_m and from_n=to_n, and godir=0.
from_m | starting coordinate, row number |
to_m | goal coordinate, row number |
from_n | starting coordinate, column number |
to_n | goal coordinate, row number |
g | direction: 1=start going vertically, 2=start going horizontally |
L | number of permitted steps |
Note that smaller cycles may appear as longer cycles when using this method. More specifically, suppose the method is run with a given L and there are cycles in the neighborhood of (from_m,from_n) of length L-2 or less, but which do not contain (from_m,from_n). These shorter cycles may then also be reported as a cycle of length L. For example, if one of the immediate neighbors of (from_m,from_n) is part of a cycle of length 4 this method will report that (from_m,from_n) is part of a cycle of length 6, if run with L=6. However, if it is known that there are no cycles of length L-2 or smaller, and check_connectivity(from_m,from_n,from_m,from_n,0,L) returns a non-negative value, then one will know with certainty that the point (from_m,from_n) is part of a cycle of length L. (This behavior is inherent to the simple recursive search used.)
Definition at line 192 of file ldpc.cpp.
References itpp::LDPC_Parity::get_col(), itpp::Sparse_Vec< T >::get_nz_indices(), itpp::LDPC_Parity::get_row(), itpp::LDPC_Parity::init_flag, it_assert, and itpp::length().
Referenced by itpp::LDPC_Parity::check_for_cycles(), and generate_random_H().
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