zishiyingsuanshubianma.txt

用MATLAB编程实现自适应的算术编码

%编码方法
str=input('请仅输入a b c d e范围内的一串随机码串:');
l=0;h=1;d=1;
p=[0.2 0.2 0.2 0.2 0.2];
geshu=ones(1,5);
n=length(str);
for i=1:n
  switch str(i)
    case 'a'
      geshu(1)=geshu(1)+1;
      m=1;
    case 'b'
       geshu(2)=geshu(2)+1;
      m=2;
    case 'c'
       geshu(3)=geshu(3)+1;
      m=3;
    case 'd'
       geshu(4)=geshu(4)+1;
      m=4;
    case 'e'
       geshu(5)=geshu(5)+1;
      m=5;
    otherwise
      error('请不要输入其它字符！');
  end
     
   pl=0;ph=0;
   for j=1:m-1 
       pl=pl+p(j);
   end
   for j=1:m 
       ph=ph+p(j);
   end
  
      l=l+d*pl;
      h=l+d*(ph-pl);
      d=h-l;
      
   p=geshu/(i+5);
end
pan=(l+h)/2

%解码方法
jieguo=str(1,n);
geshu=ones(1,5);
p=[0.2 0.2 0.2 0.2 0.2];
for i=1:n
    leiji=zeros(1,6);
    for j=1:5
        k=[1:1:j];
        leiji(j+1)=sum(p(k));
    end

   if pan>=leiji(1) & pan<leiji(2)
        jieguo(i)='a';
        geshu(1)=geshu(1)+1;
        pan=(pan-leiji(1))/(leiji(2)-leiji(1));
       
    elseif pan>=leiji(2) & pan<leiji(3)
        jieguo(i)='b';
        geshu(2)=geshu(2)+1;
        pan=(pan-leiji(2))/(leiji(3)-leiji(2));
       
    elseif pan>=leiji(3) & pan<leiji(4)
        jieguo(i)='c';
        geshu(3)=geshu(3)+1;
        pan=(pan-leiji(3))/(leiji(4)-leiji(3));
         
    elseif pan>=leiji(4) & pan<leiji(5)
        jieguo(i)='d';
        geshu(4)=geshu(4)+1;
        pan=(pan-leiji(4))/(leiji(5)-leiji(4));
         
    elseif pan>=leiji(5) & pan<leiji(6)
        jieguo(i)='e';
        geshu(5)=geshu(5)+1;
        pan=(pan-leiji(5))/(leiji(6)-leiji(5));
    end

   if i~=n
      p=geshu/(5+i);
   end
end
disp(jieguo)