get_partial_add Function

  function get_partial_add(this, upstream_grad) result(output)
    !! Get partial derivative with respect to left operand
    implicit none
    class(array_type), intent(inout) :: this
    type(array_type), intent(in) :: upstream_grad
    type(array_type) :: output

    output = upstream_grad
  end function get_partial_add