fm_calc_sc_heads Subroutine

  subroutine fm_calc_sc_heads(self)
    use mp, only: iproc, sum_allreduce
    implicit none

    class(fieldmat_type), intent(inout) :: self
    integer :: ik, is, ic, it
    !AJ There may be a problem here is any supercell has no assigned head.
    !AJ This is the case (I think) for 1,1; but it shouldn't actually cause 
    !AJ a problem as 1,1 shouldn't be communicated anyway as only one process
    !AJ is involved in it.
    self%heads = 0
    do ik=1,self%naky
       do is=1,self%kyb(ik)%nsupercell
          if(self%kyb(ik)%supercells(is)%is_head) then
             do ic=1,self%kyb(ik)%supercells(is)%ncell               
                it = self%kyb(ik)%supercells(is)%cells(ic)%it_ind
                self%heads(it,ik) = iproc
             end do
          end if
       end do
    end do

    call sum_allreduce(self%heads)

  end subroutine fm_calc_sc_heads