calculate_forbidden_region Subroutine

  subroutine calculate_forbidden_region(forbid)
    use theta_grid, only: ntgrid, bmag
    use mp, only: mp_abort
    implicit none
    logical, dimension(-ntgrid:, :), intent(out) :: forbid
    integer :: ig, il

    forbid = .false.

    ! Set the forbid flag
    do il = 1, nlambda
       do ig = -ntgrid, ntgrid
          forbid(ig,il) = 1.0 - al(il)*bmag(ig) < -bouncefuzz
       end do
    end do

    ! Check that none of our supposedly passing particles are forbidden
    ! at any point in our domain
    do il = 1, ng2
       if ( any(forbid(:,il)) ) then
          call mp_abort("Fatal error: supposedly passing particle was trapped, in calculate_forbidden_region, in le_grids.f90", .true.)
       end if
    end do
  end subroutine calculate_forbidden_region