DampPsi Subroutine

      subroutine DampPsi
      use basicmod
      use fluxmod
      implicit none
      integer :: i,j,k,n
      real(8),parameter:: alphabp=0.1d0 !
      real(8):: taui
      real(8):: dhl,dh1l,dh2l,dh3l
      real(8),parameter:: huge=1.0d90 

!$acc kernels  
      dh1l=huge
      dh2l=huge
      dh3l=huge
!$acc loop collapse(3) independent
      do k=ks,ke
      do j=js,je
      do i=is,ie
            dh1l = x1a(i+1)-x1a(i)
            dh2l = x2a(j+1)-x2a(j)
            dh3l = x3a(k+1)-x3a(k)

         dhl = min(dh1l,dh2l,dh3l)
         taui = alphabp * chg /dhl ! cm/s /cm => 1/s
         bp(i,j,k) = bp(i,j,k)*(1.0d0 - dt*taui) ! if dt = dtloc, damping by factor of (1.0-drate)
      enddo
      enddo
      enddo
!$acc end kernels

      return
end subroutine  DampPsi