get_partial_piecewise Function

  function get_partial_piecewise(this, upstream_grad) result(output)
    !! Get partial derivative of piecewise activation
    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 => merge( &
         upstream_grad, &
         upstream_grad * this%right_operand%val(1,1), &
         this%left_operand%val.le.-this%right_operand%val(2,1) .or. &
         this%left_operand%val.ge.this%right_operand%val(2,1) &
    )
    call output%assign_and_deallocate_source(ptr)

  end function get_partial_piecewise