编程练习：Arnold图像置乱算法

%Arnold变换,这个文件保存为arnold.m.

% Arnold transform, v2, 2012-02-18

% Piotr Sklodowski, <piotr.sk@gmail.com>

%

% @in: two dimensional matrix

% @iter: number of iterations

%

function [ out ] = arnold( in, iter )

   if (ndims(in) ~= 2)

       error('Oly two dimensions allowed');

   end

   [m n] = size(in);

   if (m ~= n)

       error(['Arnold Transform is defined only for squares. ' ...

       'Please complete empty rows or columns to make the square.']);

   end

   out = zeros(m);

   n = n - 1;

   for j=1:iter

       for y=0:n

           for x=0:n

               p = [ 1 1 ; 1 2 ] * [ x ; y ];

               out(mod(p(2), m)+1, mod(p(1), m)+1) = in(y+1, x+1);

           end

       end

       in = out;

   end

end

%%%%%%%%%%%%  以下是Arnold逆变换，保存为iarnold.m%%%%%%%%%%%%%%

% Inverse Arnold transform, v2, 2012-02-18

% Piotr Sklodowski, <piotr.sk@gmail.com>

%

% @in: two dimensional matrix

% @iter: number of iterations

%

function [ out ] = iarnold( in, iter )

   if (ndims(in) ~= 2)

       error('Oly two dimensions allowed');

   end

   [m n] = size(in);

   if (m ~= n)

       error(['Arnold Transform is defined only for squares. ' ...

       'Please complete empty rows or columns to make the square.']);

   end

   out = zeros(m);

   n = n - 1;

   for j=1:iter

       for y=0:n

           for x=0:n

               p = [ 2 -1 ; -1 1 ] * [ x ; y ];

               out(mod(p(2), m)+1, mod(p(1), m)+1) = in(y+1, x+1);

           end

       end

       in = out;

   end

end

%%%%%%%%%%%%%%%%具体执行方法%%%%%%%%%%%%%