fm_make_subcom_2 Subroutine

  subroutine fm_make_subcom_2(self)
    use mp, only: split, free_comm, mp_undefined
    implicit none
    class(fieldmat_type), intent(inout) :: self
    integer :: ik, colour
    type(comm_type) :: tmp
    logical :: has_head_sc

    !Make child subcommunicators
    do ik=1,self%naky
       !Make individual subcom
       call self%kyb(ik)%make_subcom_2
    enddo

    !Now make the supercell head communicator used for field gathers
    !/First work out if this proc is the head of any supercells
    has_head_sc=.false.
    do ik=1,self%naky
       has_head_sc=has_head_sc.or.any(self%kyb(ik)%supercells%is_head)
    enddo
    !/Now split to make a subcom
    colour = mp_undefined
    !NOTE: Here we assume that the supercell head will always
    !have the data we want *but* currently in ky_get_field we don't
    !store anything on the procs for which the supercell is local but 
    !empty. This should really be changed as whilst empty procs don't
    !have any field data to calculate they will still need it when
    !advancing g etc.
    if(has_head_sc.or.self%fm_sub_all%proc0) colour=1
    call split(colour,tmp,self%fm_sub_all%id)
    if(colour /= mp_undefined) then
       !/Store subcom
       self%fm_sub_headsc_p0=tmp
    endif

  end subroutine fm_make_subcom_2