get_partial_unpack_indices Function

  function get_partial_unpack_indices(this, upstream_grad) result(output)
    implicit none
    class(array_type), intent(inout) :: this
    type(array_type), intent(in) :: upstream_grad
    type(array_type) :: output
    type(array_type), pointer :: ptr

    ptr => pack(upstream_grad, this%indices, this%adj_ja(1,1))
    call output%assign_and_deallocate_source(ptr)
  end function get_partial_unpack_indices