diff --git a/tracy/tracy/src/physlib.cc b/tracy/tracy/src/physlib.cc
index 14d06f6343c2d0c997cef41b4322ffbd24ed6e75..4620ec860ca67ef97abb44405e3624e28473dd09 100644
--- a/tracy/tracy/src/physlib.cc
+++ b/tracy/tracy/src/physlib.cc
@@ -6,9 +6,9 @@
  L. Nadolski   SOLEIL        2002          Link to NAFF, Radia field maps
  J. Bengtsson  NSLS-II, BNL  2004 -
  */
-/* Current revision $Revision: 1.12 $
+/* Current revision $Revision: 1.13 $
  On branch $Name: not supported by cvs2svn $
- Latest change by $Author: nadolski $
+ Latest change by $Author: zhang $
 */
 
 /**************************/
@@ -368,7 +368,25 @@ void recalc_S(void) {
         Cell[k].S = S_tot;
     }
 }
-
+/**************************************************************************
+getcod(double dP, long &lastpos)
+
+   Purpose:
+       Find the closed orbit for the particle with energy offset dP
+       
+   Input:
+       imax number of iteration for cod search
+       dP   particle energy offset
+       eps  accuracy for cod search
+       
+   Output:
+   
+   Return:
+   
+   
+   Comments: 
+      
+***************************************************************************/       
 bool getcod(double dP, long &lastpos) {
     return GetCOD(globval.CODimax, globval.CODeps, dP, lastpos);
 }
diff --git a/tracy/tracy/src/t2cell.cc b/tracy/tracy/src/t2cell.cc
index 91ad983d776d4d6c8d3f880ab4f312f20e63f2cb..8783256c2caafee2f168fbe1107807a3c527b284 100644
--- a/tracy/tracy/src/t2cell.cc
+++ b/tracy/tracy/src/t2cell.cc
@@ -202,14 +202,17 @@ void Cell_Pass(const long i0, const long i1, ss_vect<T> &x, long &lastpos)
        lost at the aperture located at this element, finally return the value of lastpos.
 
    Input:
-       i0  starting position
-       i1 ending position of the element in the lattice
+       i0             starting position
+       i1             ending position of the element in the lattice
+       x              initial coordinates
+       lastpos        position of the last element when the particle is stable  
 
    Output:
        map     DA map
        lastpos pointer to last position of the particle
 
    Return:
+           x     position of the particle
       lastpos   
                 =position of the last element, particle is not lost
                !=position of the last element, particle is lost
@@ -761,10 +764,10 @@ bool Cell_GetCOD_M(long imax, double eps, double dP, long &lastpos)
               Looks for a chromatic closed orbit at dP  and computes oneturn map
               Search at precision eps and with a maximum of imax iterations
               using DA method
-	      If can't find the COD, then write beampos.dat, cod.out, flat_file_dbg.dat for debug; and also print information 
-	      for the particle lost.
+	      If can't find the COD, then write beampos.dat, cod.out, flat_file_dbg.dat for debug; 
+	      and also print information for the particle lost.
 	      If find the cod, then get the one turn map and cell pass, and 
-	      return status.codflag
+	      return status.codflag. The searched COD is saved in globval.CODvect
              
    Input:
        imax number of iteration for cod search
@@ -775,7 +778,9 @@ bool Cell_GetCOD_M(long imax, double eps, double dP, long &lastpos)
         
 
    Return:
-       status.codflag   true stable, false unstable.
+      globval.CODvect   COD for the particle with energy offset dP
+       status.codflag   if true, particle is stable, 
+                        if false, particle is unstable.
 
    Global variables:
        none
@@ -895,7 +900,20 @@ bool Cell_getCOD(long imax, double eps, double dP, long &lastpos)
 /********************************************************
 bool GetCOD(long imax, double eps, double dP, long &lastpos)
 
-  Purpose:
+  Purpose: Get the closed orbit for the particle with energy spread dP
+  
+  Input:
+       imax number of iteration for cod search
+       dP   particle energy offset
+       eps  accuracy for cod search
+        
+  Output:
+  
+  
+  Return:
+    lastpos     last position when the particle is stale
+        cod     the bool status whether the COD is found or not      
+       
     
 ********************************************************/