rotlatt.m

Lattice coding and decoding

function varargout = rotlatt(latt,varargin)

%ROTLATT Lattice rotation
%   RL = ROTLATT(L) applies a rotation operator to the lattice of
%   arbitary dimension. 
%
%   RL = ROTTLATT(L,PWR) applies a rotation operator powered to the PWR. 
%
%   [RL,R] = ROTLATT(L,PWR) same as above but also returns rotation
%   operator R.
%
%   Example:
%       We verify the relation R^2(Z2) = 2I(Z2) = 2Z2
%
%       pts = 2 ^ 4;
%       Z2 = makelatt('Z',pts,2);
%       IZ2 = rotlatt(Z2,2);
%       showlatt(Z2,'Style',1); hold on;
%       showlatt(Z2,'Labeling','num');
%
%   See also SPAN, GETPARAMS.

%   Copyright 2001-2003 Kamil Anis, [e-mail]
%   Dept. of Radioelectronics, 
%   Faculty of Electrical Engineering
%   Czech Technical University in Prague
%   $Revision: 0.1 $  $Date: 2003/1/16 17:33:28 $
%   --
%   <additional stuff goes here>

if isempty(varargin) == 1
	pwr = 1; % default value
else
	pwr = varargin{1};
end

[m,n] = size(latt);

k = 1:n / 2;
l = 1:n / 2 - 1;

diag_main = ones(n,1);
diag_main(2*k) = -1;
diag_lateral = ones(n - 1,1);
diag_lateral(2 * l) = 0;
R = diag(diag_main) + diag(diag_lateral,1) + diag(diag_lateral,-1);

for i = 1:m
  rotated(i,:) = latt(i,:) * (R ^ pwr);
end

varargout = {rotated,R};