SUBROUTINE  calcul(  u,  f  )
      USE MPI
      USE numerics
      IMPLICIT  NONE
      REAL(rp),  DIMENSION(sx-1:ex+1,sy-1:ey+1,sz-1:ez+1,0:1),  INTENT(INOUT)   ::  u
      REAL(rp),  DIMENSION(sx-1:ex+1,sy-1:ey+1,sz-1:ez+1),      INTENT(IN)      ::  f
      END SUBROUTINE calcul