codage huffman avec matlab
salut tout le monde on nous a demandé de faire un programme (sans utiliser la commande) qui donne les code de chaque symbole introduit alor j'ai trouvé un code mais je n'ai pas compris quelque ligne
voici le code
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| function [code,compression]=huffman5(p);
%HUFFMAN5
%HUFFMAN CODER FOR V5
% Format [CODE,COMPRESSION]=HUFFMAN5(P)
%
% P is the probability (or number of occurences) of each alphabet symbol
% CODE gives the huffman code in a string format of ones and zeros
% COMPRESSION gives the compression rate
%
% Huffman5 works by first building up a binary tree (eg p =[ .5 .2 .15 .15])
%
% a_1 a_4
% 1/ 1/
% / /
% b3 b1
% \ / \
% 0\ 1/ 0\
% b2 a_3
% \
% 0\
% a_2
%
% Such that the tree always terminates at an alphabet symbol and the
% symbols furthest away from the root have the lowest probability.
% The branches at each level are labeled 0 and 1.
% For this example CODE would be
% 1
% 00
% 010
% 011
% and the compression rate 1.1111
% Sean Danaher University of Northumbria at Newcastle UK 98/6/4
p = input('entrez le vecteur des probabilité');
p=p(:)/sum(p); %normalises probabilities
c=huff5(p);
code=char(getcodes(c,length(p)));
compression=ceil(log(length(p))/log(2))/ (sum(code' ~= ' ')*p);
%---------------------------------------------------------------
function c=huff5(p);
% HUFF5 Creates Huffman Tree
% Simulates a tree structure using a nested cell structure
% P is a vector with the probability (number of occurences)
% of each alphabet symbol
% C is the Huffman tree. Note Matlab 5 version
% Sean Danaher 98/6/4 University of Northumbria, Newcastle UK
c=cell(length(p),1); % Generate cell structure
for i=1:length(p) % fill cell structure with 1,2,3...n
c{i}=i; % (n=number of symbols in alphabet)
end
while size(c)-2 % Repeat till only two branches
[p,i]=sort(p); % Sort to ascending probabilities
c=c(i); % Reorder tree.
c{2}={c{1},c{2}};c(1)=[]; % join branch 1 to 2 and prune 1
p(2)=p(1)+p(2);p(1)=[]; % Merge Probabilities
end
%---------------------------------------------------------------
function y= getcodes(a,n)
% Y=GETCODES(A,N)
% Pulls out Huffman Codes for V5
% a is the nested cell structure created by huffcode5
% n is the number of symbols
% Sean Danaher 98/6/4 University of Northumbria, Newcastle UK
global y
y=cell(n,1);
getcodes2(a,[])
%----------------------------------------------------------------
function getcodes2(a,dum)
% GETCODES(A,DUM)
%getcodes2
% called by getcodes
% uses Recursion to pull out codes
% Sean Danaher 98/6/4 University of Northumbria, Newcastle UK
global y
if isa(a,'cell')
getcodes2(a{1},[dum 0]);
getcodes2(a{2},[dum 1]);
else
y{a}=setstr(48+dum);
end |
ca veut dire quoi dans matlab lorsqu'on ecris une matrice entre 2 acolade {}
tel que :
Code:
c{2}={c{1},c{2}};c(1)=[];
et puis dans la 2eme fonction je n'ai rien pigé tel que
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| global y
if isa(a,'cell')
getcodes2(a{1},[dum 0]);
getcodes2(a{2},[dum 1]);
else
y{a}=setstr(48+dum);
end |
meme a l'aide du help j'arrive pas a me fixer les idées aidez moi svp:?
