LDPC parity check matrix generic class. More...
#include <itpp/comm/ldpc.h>
Public Member Functions  
LDPC_Parity ()  
Default constructor.  
LDPC_Parity (int ncheck, int nvar)  
Constructor that gives an empty matrix of size ncheck x nvar.  
LDPC_Parity (const std::string &filename, const std::string &format)  
Load an LDPC parity check matrix from a file.  
LDPC_Parity (const GF2mat_sparse_alist &alist)  
Constructor, from a GF2mat_sparse_alist object.  
virtual  ~LDPC_Parity () 
Virtual destructor.  
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.  
virtual void  display_stats () const 
Display some information about the 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  
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.  
Friends  
class  LDPC_Code 
LDPC parity check matrix generic class.
This class provides a basic set of functions needed to represent a parity check matrix, which defines an LDPC code. This class is used as base class for a set of specific LDPC parity check matrix classes, e.g. regular or irregular LDPC codes.
This class stores a parity check matrix as a sparse matrix. The transpose of the matrix is also stored to enable efficient access to its rows.
All parity check matrices can be loaded from (saved to) a file by converting them from (to) a portable GF2mat_sparse_alist
format.
However, typically one will want to create a LDPC_Code
from the parity check matrix (and optionally a generator) and save the codec binary data instead.
Please refer to the tutorial Generation of LDPC codes for some examples of code generation.
itpp::LDPC_Parity::LDPC_Parity  (  const std::string &  filename, 
const std::string &  format  
) 
Load an LDPC parity check matrix from a file.
filename  file name 
format  file format 
GF2mat_sparse_alist
for its definition).load_alist()
and save_alist()
Definition at line 55 of file ldpc.cpp.
References it_error, and load_alist().

protected 
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 check_connectivity(), get_col(), itpp::Sparse_Vec< T >::get_nz_indices(), init_flag, it_assert, itpp::length(), and nvar.

protected 
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 L2 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 L2 or smaller, and check_connectivity(from_m,from_n,from_m,from_n,0,L) returns a nonnegative 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 get_col(), itpp::Sparse_Vec< T >::get_nz_indices(), get_row(), init_flag, it_assert, and itpp::length().
Referenced by check_for_cycles(), and itpp::LDPC_Parity_Unstructured::generate_random_H().
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