%?This?program?constructs?coumn-weight?four?girth?8?quasi-cyclic?LDPC?codes?given
%?k（?row?weight?j（column?weight）?is?fixed?at?4）?and?m?（size?of?each?sub-matrix）.?The
%?program?constructs?a?distance?graph?first?then?converts?it?into?a?matrix.
%?For?details?of?the?algorithm?see?PhD?thesis?by?G.Malema?LDPC?codes:?Construction?and?Implementation
%（University?of?Adelaide?2007）?and?other?publications.
%?Author?:?Dr.?Gabofetswe?Alafang?MalemaUniversity?of?Botswana??
%?Department?of?Computer?science.?e-mail:?malemag@mopipi.ub.bw

j=4;?%?column-weight?should?be?fixed?at?4.
k=8;?%?row-weight?is?variable.
m=130;?%?size?of?each?sub-matrix.is?variable.
M=j*m;?%?total?number?of?rows.
shift=zeros（kj）;?%?stores?shift?values?for?each?sub-matrix.
rows?=?struct（‘connect‘0‘counter‘0‘con‘0）;?%?structure?used?for?storing?connections.
emptyset?=?[];
for?y?=?1:M???????%?connections?and?number?of?connections?for?rows?and?columns?are?initialized.
????rows（y）.counter?=?0;
????rows（y）.con?=?intersect（emptysetrows（y）.con）;
????rows（y）.connect?=?intersect（emptysetrows（y）.connect）;
????%rows（y）.mem?=?intersect（emptysetrows（y）.mem）;
end
group1?=?[1:m];??%row?group?one
group2?=?[m+1:2*m];??%?row?group?two
group3?=?[2*m+1:3*m];?%?row?group?three?these?groups?are?connected?to?group?one.
group4?=?[3*m+1:4*m];

g=?1;?%?determines?the?girth?of?the?code?in?these?case?8.
found_code?=?1;?%?true?if?algorithm?does?not?fail.

%?the?for?loop?finds?a?rows（from?groups?123）?that?are?apart?at?atleast?a?distance
%?of?8.?They?are?then?connected.?The?rest?of?the?groups?are?connected
%?according?to?this?first?connection.?The?process?is?repeated?k?times?which
%?is?the?number?of?connections?for?each?row.
for?kk?=?1:k
????r1?=?ceil（rand*length（group1））;?%?randomly?choose?a?row?from?group1
????i?=?group1（r1）;
????%while?rows（i）.counter?????????mem=[];?mem1?=?rows（i）.con;
????????mem2?=?[];
????????for?y?=?1:g
????????????%mem2?=?[];
????????????for?x?=?1:length（mem1）
????????????????x1?=?mem1（x）;
????????????????mem2?=?union（mem2rows（x1）.con）;
????????????end
????????????mem?=?union（mem1mem2）;
????????????mem1=mem;
????????end
????????
????%?find?row?not?in?mem?in?the?given?range.
????
????A?=?intersect（memgroup2）;
????A?=?setxor（Agroup2）;
????if?（isempty（A）~=1）
????????r1?=?ceil（rand*length（A））;
????????row1?=?A（r1）;
????else
????????disp（‘Row?two?not?found‘）;
????????found_code?=?0;
????????break;
????end
????
????%?create?list?of?neighbors?at?a?distance?of?6?or?less?for?row1.
????mem3?=?[];?mem1=rows（row1）.con;
????mem2?=?[];
????for?b?=?1:g
????????%mem2?=?[];
????????for?x?=?1:length（mem1）
????????????x1?=?mem1（x）;
????????????mem2?=?union（mem2rows（x1）.con）;
????????end
????????mem3?=?union（mem1mem2）;
????????mem1?=?mem3;
????end
????mem3?=?union（mem3row1）;
????
????%?Find?row?2?not?in?mem?or?mem3?at?a?distance?of?atleast?7.
????
????????????check1?=?intersect（memgroup3）;
????????????chec

?屬性????????????大小?????日期????時間???名稱
-----------?---------??----------?-----??----
?????文件????????6444??2009-05-20?07:28??girth84rr.m
?????文件????????1338??2009-05-20?07:28??license.txt