!copyright (C) 2001  MSC-RPN COMM  %%%RPNPHY%%%
***S/P  DVRTDF
*

      SUBROUTINE DVRTDF ( R , X , DS, N , MR , MX , NK ) 8
*
#include "impnone.cdk"
      INTEGER N, MR, MX, NK
      REAL R(MR,NK),X(MX,NK),DS(n,NK)
*
*Author
*          R. Benoit RPN(Mar 1989)
*
*Revisions
* 001      R. Benoit (Aug 93) - DS(2D) for Local sigma
*
*Object
*          to calculate the vertical derivative by centred finite
*          differences
*
*Arguments
*
*          - Output -
* R        result
*
*          - Input -
* X        variable to derive
* DS       distance between sigma levels 'U'
* N        horizontal dimensions
* MR       1st dimension of R
* MX       1st dimension of X
* NK       vertical dimension
*
*Notes
*          R and X can share the same space, R(*,NK)=0
*
**
*
      INTEGER J,K
*
*
      DO 30 K=1,NK-1
CDIR$ IVDEP
         DO 20 J=1,N
            R(J,K)=(X(J,K+1)-X(J,K))/DS(j,K)
  20     CONTINUE
*
  30  CONTINUE
*
      DO 40 J=1,N
         R(J,NK)=0
  40  CONTINUE
*
      RETURN
      END