CALL SEQUENCE...
      dertim  XIN XOUT OUTPUT
 
 
      AUTHOR - B.Dugas, novembre 1992.
      LAST REVISION: $Header: /home/cvs/RMNLIB/utils/rdiag/lspgm/dertim.ptn,v 4.15 2014/09/25 20:20:47 dugas Exp $
 
 
      DESCRIPTION...
       A CCC FILE ARITHMETIC PROGRAM WHICH...
 
       ... PRODUCES FILE XOUT(T) = XIN(T)-XIN(T-1)
       
       NOTES - 1) DERTIM MAKES MINIMAL USE OF XIN'S TIME INFORMATION.
                  THE FIRST SAMPLE TIME IS SIMPLY ASSIGNED T=0,
                  THE NEXT ONE IS T=1, AND SO ON.
               2) XOUT(T=0) = XIN(T=0) 
               3) XIN CAN BE MULTI-LEVEL, MULTI-VARIABLE.
                  IN THIS CASE, THE FILE IS SUPPOSED TO BE
                  SORTED ACCORDING TO TIMESTEP/NAME/LEVEL,
                  FROM MOST TO LEAST SIGNIFICANT
      
 
      EXIT CONDITIONS...
        0 NO PROBLEMS
        1 UNABLE TO READ FIRST SET
        2 MORE THAN ONE SIZE IN XIN
        3 UNABLE TO ALLOCATE ENOUGH WORKING MEMORY