求解R中函数的逆

Is there any way for R to solve for the inverse of a given single variable function? The motivation is for me to later tell R to use a vector of values as inputs of the inverse function so that it can spit out the inverse function values.

有没有办法让R求解给定单变量函数的逆？我的动机是让我稍后告诉R使用值向量作为反函数的输入，以便它可以吐出反函数值。

For instance, I have the function y(x) = x^2, the inverse is y = sqrt(x). Is there a way R can solve for the inverse function?

例如，我有函数y（x）= x ^ 2，反函数是y = sqrt（x）。 R有没有办法解决反函数？

I looked up uniroot(), but I am not solving for the zero of a function.

我查找了uniroot（），但我没有解决函数的零点问题。

Any suggestions would be helpful.

任何的意见都将会有帮助。

Thanks!

谢谢！

1 个解决方案

#1

What kind of inverse are you finding? If you're looking for a symbolic inverse (e.g., a function y that is identically equal to sqrt(x)) you're going to have to use a symbolic system. Look at ryacas for an R library to connect with a computer algebra system that can likely compute inverses, Yacas.

你发现了什么样的逆转？如果您正在寻找符号反转（例如，函数y与sqrt（x）相同），则您将不得不使用符号系统。查看ryacas的R库以连接计算机代数系统，它可能会计算逆，Yacas。

Now, if you need only to compute point-wise inverses, you can define your function in terms of uniroot as you've written:

现在，如果你只需要计算逐点逆，你可以按照你所写的uniroot来定义你的函数：

> inverse = function (f, lower = -100, upper = 100) {
   function (y) uniroot((function (x) f(x) - y), lower = lower, upper = upper)[1]
}

> square_inverse = inverse(function (x) x^2, 0.1, 100)

> square_inverse(4)
[1] 1.999976

For a given y and f(x), this will compute x such that f(x) = y, also known as the inverse.

对于给定的y和f（x），这将计算x使得f（x）= y，也称为逆。

#1