nbhood.m

Lattice coding and decoding

function pts = nbhood(latt,element,varargin)

%NBHOOD Find lattice element neighbors
%   NH = NBHOOD(L,P) finds the element's P neighbours along the
%   equilateral axes. There's a slight difference between NBHOOD and
%   SSHELL function. The following examle tells all.
%
%   Example:
%       pts = 2 ^ 5;
%       Z2 = makelatt('Z',pts,2);
%       NH = nbhood(Z2,13)
%       showlatt(NH,'Style',1); hold on;
%       showlatt(Z2,'Labeling','num');
% 
%       figure;
%       SH = sshell(Z2,13);
%       showlatt(SH,'Style',2); hold on;
%       showlatt(Z2,'Labeling','num');
%
%   Note: NBHOOD function gives sensible results only for geometrically
%         uniform lattices.
%
%   See also SSHELL, KISS.

%   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>

name = 'NBHOOD';
[idt,tag] = iecho(name);

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% set shell thickness
if nargin == 3
	thick = varargin{1};
else 
	thick = 1; % default thickess
end

[npts,dim] = size(latt);

% check the element position
if (npts < element) | (element < 0)
	disp(' ');
	disp([tag,'Not a lattice element!']);
	disp([idt,'Setting element to 1.']);
	disp(' ');
	
	element = 1;
end

coord = latt(element,:);
center = repmat(coord,[npts 1]);
dist = abs(latt - center);

% find smallest non-zero element
% 0 -> realmax
q = mapsto(dist,0,realmax);
m = min(min(q));

q100 = mapsto(dist,0,100)
z = unique(q100)

%m = min(min(q));

% STEP I: throw out the elements greater than m
y = (dist <= m);
u = prod(y,2);
r = find(u == 1);

%u = sum(y,2);
%r = find(u > 0);

% STEP II: find those with zero distance from the rest (lie on the axis)
x = (dist == 0);
w = sum(x,2);
s = find(w > 0); 

% find the intersection of both
pos = intersect(r,s);

% removing query point from the nbhood set
pt = find(pos == element);
pos = pos([1:pt - 1 pt + 1:end]);

pts = latt(pos,:);

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