SUBROUTINE DMDER
C     ================
C
      INCLUDE 'IMPLIC.FOR'
      INCLUDE 'BASICS.FOR'
      INCLUDE 'ATOMIC.FOR'
      INCLUDE 'MODELQ.FOR'
      COMMON/DEPTDR/DDM(MDEPTH),DDP(MDEPTH),DD0(MDEPTH),
     *              DDMIN(MDEPTH),DDPLU(MDEPTH),DDA(MDEPTH),
     *              DDC(MDEPTH),DDB(MDEPTH)
C
      DO ID=2,ND-1
         DDM(ID)=DM(ID)-DM(ID-1)
         DDP(ID)=DM(ID+1)-DM(ID)
         DD0(ID)=DM(ID+1)-DM(ID-1)
         DDMIN(ID)=DDP(ID)/DD0(ID)
         DDPLU(ID)=DDM(ID)/DD0(ID)
         DDA(ID)=DDMIN(ID)/DDM(ID)
         DDC(ID)=DDPLU(ID)/DDP(ID)
      END DO
C
      DDM(1)=0.
      DDM(ND)=DM(ND)-DM(ND-1)
      DDP(1)=DM(2)-DM(1)
      DDP(ND)=0.
      DDMIN(1)=0.
      DDMIN(ND)=1.
      DDPLU(1)=1.
      DDPLU(ND)=0.
      DDA(1)=0.
      DDA(ND)=UN/DDM(ND)
      DDC(1)=UN/DDP(1)
      DDC(ND)=0.
      DO ID=1,ND
         DDB(ID)=DDA(ID)-DDC(ID)
      END DO
C
      RETURN
      END