Solution

 SUBROUTINE DoIt(X,Y,Z,n)
  IMPLICIT NONE
   INTEGER, INTENT(IN)                 :: n
   REAL, DIMENSION(:,:), INTENT(INOUT) :: X
   REAL, DIMENSION(:,:), INTENT(IN)    :: Y,Z
    WHERE (ABS(X) .GE. 0.01) X = (Y*Z*n)/X
 END SUBROUTINE DoIt

and in the calling program

  INTERFACE
   EXTRINSIC(F90_LOCAL) SUBROUTINE DoIt(X,Y,Z,n)
     IMPLICIT NONE
      INTEGER, INTENT(IN)                 :: n
      REAL, DIMENSION(:,:), INTENT(INOUT) :: X
      REAL, DIMENSION(:,:), INTENT(IN)    :: Y,Z
!HPF$ PROCESSORS, DIMENSION(10,10)        :: P
!HPF$ ALIGN (:,:) WITH X(:,:)             :: Y, Z
!HPF$ DISTRIBUTE (CYCLIC,CYCLIC) ONTO P   :: X
    END SUBROUTINE DoIt
  END INTERFACE