allweight.m

一个很有用的函数

function v = allweight(n, w)  
% v = allweight(n, w)  
%
% Computes all binary n-vectors with weight w.
%
% Inputs:
%   n = length of vector
%   w = weight of vectors (w <= n)
%
% Output:
%   v = matrix of vectors with weight w, Nxn
%       N = nchoosek(n, w) = number of binary n-vectors of weight w
%
% Release: $Name:  $
% Version: $Id: allweight.m,v 1.2 2005-11-24 09:19:26+01 estrom Exp $

% History:
% 
% Original by Anders Persson
% Erik Str鰉, 010320 
% Erik Str鰉, bug fixed for MATLAB 7, 051124

if w > n
    error('Weight of code word > length of code word!');
end
if ( (n > w) & (w > 0) ) %% Recursive!
    v = zeros(nchoosek(n, w), n);
    n1 = nchoosek(n-1, w-1);
    v(1:n1, 1) = ones(n1, 1);
    v(1:n1, 2:end) = allweight(n-1, w-1);
    n0 = nchoosek(n-1, w);
    v(n1+(1:n0), 2:end) = allweight(n-1, w);
else %% Done!
  if w == 0 
    v = zeros(1, n);
  else
    v = ones(1, w);
  end    
end