从派生命令中提取渐变 [英] Extract the gradient from the deriv command

问题描述

前几天，一位同事问我以下问题.在下面的代码中，如何提取渐变:

A colleague asked me the following question the other day. In the following piece of code, how do you extract the gradient:

> x=5
> a = eval(deriv(~ x^3, "x"))
> a
[1] 125
attr(,"gradient")
      x
[1,] 75

我的回答是

>  attr(a, "gradient")[1]
[1] 75

这个语法对我来说似乎很笨拙.有没有更好的提取梯度的方法?

This syntax seems clunky to me. Is there a better way of extracting the gradient?

推荐答案

不确定这些算作更好，但是:

Not sure these count as better, but:

with(attributes(a), gradient)

或

attributes(a)$gradient

是将属性返回为可供选择的列表的替代方法.

are alternatives that return the attributes as a list from which to select.

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