diff --git a/tt.m b/tt.m
index 7cb13f97e9e4cce6b54075d0ac06406a7ffd6d94..0ee8045a9ed8c46067c5fe01fe68070e3dbda702 100644
--- a/tt.m
+++ b/tt.m
@@ -1,4 +1,4 @@
-function [a_out, b_out]=tt(x)
+function [a_out, b_out, c_out]=tt(x)
 % TT   Mean trapping time and its distribution.
 %    A=TT(X) computes the mean of the length of the vertical 
 %    line structures in a recurrence plot, so called trapping 
@@ -23,6 +23,9 @@ function [a_out, b_out]=tt(x)
 % $Revision$
 %
 % $Log$
+% Revision 3.3  2005/11/23 07:29:14  marwan
+% help text updated
+%
 % Revision 3.2  2005/03/16 11:19:02  marwan
 % help text modified
 %
@@ -36,30 +39,25 @@ function [a_out, b_out]=tt(x)
 % of the License, or any later version.
 
 error(nargchk(1,1,nargin));
-if nargout>2, error('Too many output arguments'), end
+if nargout>3, error('Too many output arguments'), end
+    
+%a_out = NaN; b_out = NaN; c_out = NaN;
 
 warning off
 if any(x(:))
 
-  if min(size(x))>1000       % this should speed up the routine; the value
-                             % depends on the available memory
-    x2=uint8(x);
-    x2(end+1,:)=0;
-    x=reshape(x2,size(x2,1)*size(x2,2),1);
-    x2=x(2:end);x(end)=[];
-    z0=find(x==0&x2==1);
-    z1=find(x2==0&x==1);
-  
-  else
-  
-    x(end+1,:)=0;x=double(x);
-    z=diff(reshape(x,size(x,1)*size(x,2),1));
-    z0=find(~(z-1));
-    z1=find(~(z+1));
-  
-  end
-  
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% for black vertical lines
+    xb=double(x); 
+    xb(end+1,:)=0;xb=double(xb(:));
+    z=diff(xb);
+    z0=find(z==1); % begin of black sequence
+    z1=find(z==-1); % end of black sequence
   
+
+  % measure the length of black lines
   if z0(1)>z1(1)
     z0(2:end+1)=z0(1:end);z0(1)=0; 
     if length(z0)>length(z1) 
@@ -69,8 +67,43 @@ if any(x(:))
   
   t=sort(z1-z0);
   t1=t(find(t-1));
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% for white vertical lines
+  for i = 1:size(x,2)
+      i_ = find(x(:,i));
+      i1 = min(i_); i2 = max(i_);
+      x(1:i1,i) = 1;
+      x(i2:end,i) = 1;
+  end
+  
+    xw=double(x); xw(end+1,:)=1;
+    zw=diff(xw(:));
+    z0w=find(zw==-1); % begin of white sequence
+    z1w=find(zw==1); % end of white sequence
+
+
+  
+  % measure the length of white lines
+  if z0w(1)>z1w(1)
+    z0w(1)=[]; 
+    if length(z1w)>length(z0w) 
+       z1w(end)=[];
+    end
+  end
+  if length(z1w)>length(z0w) 
+       z0w=[1;z0w];
+  end
+  
+  tw=sort(z1w-z0w);
+  t1w=tw(find(tw-1));
   
-  if nargout==2
+  if nargout==3
+     c_out=zeros(length(tw),1);
+     c_out=tw;
+  end
+  
+  if nargout>=2
      b_out=zeros(length(t),1);
      b_out=t;
   end
@@ -85,7 +118,11 @@ if any(x(:))
     
 else
 
-  if nargout==2
+  if nargout==3
+     c_out=NaN;
+  end
+ 
+  if nargout>=2
      b_out=NaN;
   end