no4cycles.m

一些奇偶校验矩阵的构造-matlab 消除四环

% Function searches for the presence of 4-cycles in the parity check matrix H
%
%   Prasanna Sethuraman, March 2004.
%

% 'row','col' is the postion in which a 1 is to be added. This function
% checks whether a 4-cycle is formed if a one is added at (row,col) in the
% existing H matrix.
function [no4cycle] = no4cycles(H, row, col)

onesInRow = find(H(row,:));

dim=size(H);
M = dim(1);
N = dim(2);

no4cycle=true;
for i=1:length(onesInRow)
    onesInCol = find(H(:,onesInRow(i)));
    for j=1:length(onesInCol)   
        if ( H(onesInCol(j),onesInRow(i))==1 & H(onesInCol(j),col)==1 & col~=onesInRow(i) & row~=onesInCol(j))
            no4cycle=false;
            return;
        end;
    end;
end;
% no4cycle