function [h,l]=huffman(p);
%HUFFMAN 	Huffman code generator
%	 	[h,l]=huffman(p), Huffman code generator
%	 	returns h the Huffman code matrix, and l the
%        	average codeword length for a source with 
%	 	probability vector p. 

if length(find(p<0))~=0,
  error('Not a prob. vector, negative component(s)')%概率不能小于0
end
if abs(sum(p)-1)>10e-10,
  error('Not a prob. vector, components do not add up to 1')%總概率必須=1
end
n=length(p);%n是q中元素的個數
q=p;
m=zeros(n-1,n);
for i=1:n-1
  [q,l]=sort(q);%把q的元素按照降序排列放到q中,
  m(i,:)=[l(1:n-i+1),zeros(1,i-1)];%m矩陣中第一列是所有的l，第二列是去掉最小的一個，依次類推，其他用0填滿
  q=[q(1)+q(2),q(3:n),1];
end
for i=1:n-1
  c(i,:)=blanks(n*n);%返回n的平方個空位,最后是n-1行，n方列
end
c(n-1,n)='0';
c(n-1,2*n)='1';
for i=2:n-1
  c(n-i,1:n-1)=c(n-i+1,n*(find(m(n-i+1,:)==1))...%表示延續到下一行
  -(n-2):n*(find(m(n-i+1,:)==1)));
  c(n-i,n)='0';
  c(n-i,n+1:2*n-1)=c(n-i,1:n-1);
  c(n-i,2*n)='1';
  for j=1:i-1
    c(n-i,(j+1)*n+1:(j+2)*n)=c(n-i+1,...
    n*(find(m(n-i+1,:)==j+1)-1)+1:n*find(m(n-i+1,:)==j+1));
  end
end
for i=1:n
  h(i,1:n)=c(1,n*(find(m(1,:)==i)-1)+1:find(m(1,:)==i)*n);
  l1(i)=length(find(abs(h(i,:))~=32));
end
l=sum(p.*l1);