some comments added

hist2.m

@@ -25,7 +25,7 @@ function varargout=hist2(varargin)
 %
 %    See also HIST, HISTN, BAR3, MI.
 
-% Copyright (c) 2002-2003
+% Copyright (c) 2002-2007
 % Andre Sitz, Norbert Marwan, Potsdam University, Germany
 % http://www.agnld.uni-potsdam.de
 %
@@ -33,6 +33,9 @@ function varargout=hist2(varargin)
 % $Revision$
 %
 % $Log$
+% Revision 1.10  2006/07/04 14:05:08  marwan
+% lag = zero allowed
+%
 % Revision 1.9  2004/11/10 07:05:37  marwan
 % initial import
 %
@@ -82,15 +85,21 @@ if size(x,1)<size(x,2), x=x';end
 if size(y,1)<size(y,2), y=y';end
 x=x(:,1); y=y(:,1);
 %x=x(:); y=y(:);
-x1=(x-min(x))/max(x-min(x))-eps;
-y1=(y-min(y))/max(y-min(y))-eps;
+
+% normalise the value range to [0 1)
+x1 = (x - min(x)) / max(x - min(x)) - eps;
+y1 = (y - min(y)) / max(y - min(y)) - eps;
+
 if length(x)<=lag, lag=length(x)-1; warning(['Lag is too large. Using ',num2str(lag),' instead.']), end
 
-temp=fix(x1(1:(end-lag))*nbin)+(fix(y1((lag+1):end)*nbin))*nbin;
+% this is the main trick: put the first data to values [1:1:nbin] and the second data to [nbin:nbin:nbin^2]
+temp = fix(x1(1:(end-lag)) * nbin) + (fix(y1((lag+1):end) * nbin)) * nbin;
 
+% call Matlab histc function (faster than hist)
 p=histc(temp,0:(nbin^2-1))';
 p2=reshape(p,nbin,nbin)/length(x);
 
+% create the correct bin denominator
 minx = min(min(x)); maxx = max(max(x));
 if minx == maxx, minx = minx - floor(nbin/2) - 0.5; maxx = maxx + ceil(nbin/2) - 0.5; end
 miny = min(min(y)); maxy = max(max(y));