get_partial_tanh Function

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

    logical :: this_is_temporary_local
    type(array_type), pointer :: ptr

    this_is_temporary_local = this%is_temporary
    this%is_temporary = .false.
    ! derivative of tanh(x) is (1 - tanh(x)^2)
    ptr => upstream_grad * tanh_reverse_array(this)
    ! ptr => upstream_grad * (1._real32 - this ** 2._real32)
    this%is_temporary = this_is_temporary_local
    call output%assign_and_deallocate_source(ptr)
  end function get_partial_tanh