anchor.diff:        DIMENSION VT1W(MAXEQ,MAXND),VT2W(MAXEQ,MAXND)
         DIMENSION DN_S(MAXND),DN(MAXND)
         DIMENSION ICHECK(8)
  +CMWF LOCAL VARIABLES
  +      INTEGER IDEBUG,II,KK,ISTEPOUTSIDE
   C
   C =================== START PT USING ADAPTIVE RK ====================
   C
  
positive.code: C IF THE ENDING LOCATION CAN BE CONSIDERED ON THE ELEMENT BOUNDARY
  C ==> NO NEED TO REDUCE TIMESTEP
  C
                IF(DABS(D2*DL).LE.ATOL)GOTO 150
  C
  C IF THE ENDING LOCATION IS TRULY OUTSIDE OF THE ELEMENT
  C ==> COMPUTE AN INTERPOLATION FACTOR
  C
                XSI=DMAX1(XSI,D12/D1)
              ENDIF
            ENDIF
    150   CONTINUE
  
negative.code: C    ===> COMPUTE XSI
  C
            IF(DN(I).LT.0.0E0)THEN
               ISTEPOUTSIDE = 1
               IF (IDEBUG.GT.0) THEN
  C MWF DEBUG
                  WRITE(6,*)' DN(',I,')= ',DN(I),' OUTSIDE ELEMENT'
               ENDIF
              D1=DN_S(I)
              D2=DN(I)
              D12=DN_S(I)-DN(I)
  C
  C A1. WHEN THERE IS NO TRACKIING THROUGH THIS ELEMENT
  C
  C MWF 9/30/10           
  C            IF(DABS(D1*DL).LT.ATOL)THEN
              IF (DABS(D1).LT.DN_SAFE)THEN
  C     
  C IF THE PT IS LEAVING THE ELEMENT
  C ==> SET IDSDT TO 0, AND IDENTIFY I1, I2, I3 TO
  C     CONDUCT PT IN AN ADJACENT ELEMENT
  C
  CMWF 9/30/10
  C              IF(DABS(D2*DL).GT.ATOL)THEN
  C ALSO HAD ATOL IN DN_CHECK
                 IF(DABS(D2).GT.DN_SAFE)THEN
                  CALL DN_CHECK
       I              (MAXND,NODE,NEQ, DL,DN_SAFE,
       I               DN_S,
       O               I1,I2,I3)
                  IDSDT=0
  C MWF DEBUG
                  IF (IDEBUG.GT.0) THEN
                     WRITE(6,*)' ELTRAK DN_CHECK LEAVING IDSDT= ',IDSDT, 
       &                  ' I1= ',I1,' I2= ',I2,' I3= ',I3, 
       &                  ' D1= ',D1, ' D2= ',D2,' D12= ',D12
                  ENDIF
                  RETURN
                ENDIF
  C
  