SUBROUTINE  prodscal(  rnorm,  a,  b,  comm3d  )
      USE numerics
      IMPLICIT  NONE
      REAL(rp),  INTENT(OUT)   ::  rnorm
      REAL(rp),  DIMENSION(  sx-1:ex+1,  sy-1:ey+1,  sz-1:ez+1),  INTENT(IN)  ::  a
      REAL(rp),  DIMENSION(  sx-1:ex+1,  sy-1:ey+1,  sz-1:ez+1),  INTENT(IN)  ::  b
      INTEGER,   INTENT(IN)  ::  comm3d
      END  SUBROUTINE  prodscal