function [ meanDistSqr, dist2Lth ] = mDSTLNN( data, L )
%
% This function returns the average of the squared distance between each
% point and its L'th nearest neighbor.  I.E. when L=1 we return the average
% of the square of the nearest neighbor distance.
% 
% Written by:
% -- 
% John L. Weatherwax                2005-08-14
% 
% email: wax@alum.mit.edu
% 
% Please send comments and especially bug reports to the
% above email address.
% 
%-----

nSamp = size(data,1); 
if( L > nSamp )
  error( 'L must be less than the number of samples' ); 
end

% Compute the ((distance to Lth)^2) FROM each sample TO each sample:
dist2Lth = zeros(1,nSamp);
for ii=1:nSamp,
  xt = data(ii,:); 
  % Compute the squared distance between the datum xt and ALL other datum:
  dist = zeros(1,nSamp); 
  for jj=1:nSamp,
    yt = data(jj,:); 
    diff = xt - yt; 
    distSqr(jj) = diff * (diff.'); 
  end
  [ws,wi] = sort(distSqr);   
  dist2Lth(ii) = ws(L+1);
end

meanDistSqr = mean( dist2Lth );