numpy.polyval()的反函数 [英] Inverse function of numpy.polyval()

问题描述

我想知道np.polyval()是否有一个方便的逆函数，我在其中给出y值并求解x?

I was wondering is there a convenient inverse function of np.polyval(), where I give the y value and it solves for x?

我知道我可以做到这一点的一种方法是:

I know one way I could do this is:

import numpy as np

# Set up the question
p = np.array([1, 1, -10])
y = 100

# Solve
p_temp = p
p_temp[-1] -= y
x = np.roots(p_temp)

不过，我的猜测最多的是，该代码的可读性差.有什么建议吗?

However my guess is most would agree on that this code has low readability. Any suggestions?

推荐答案

这样的事情怎么样?

In [19]: p = np.poly1d([1, 1, -10])  # Use a poly1d to represent the polynomial.

In [20]: y = 100

In [21]: (p - y).roots
Out[21]: array([-11.,  10.])

poly1d对象实现算术运算以返回新的poly1d对象，因此p - y是新的poly1d:

The poly1d object implements the arithmetic operations to return a new poly1d object, so p - y is a new poly1d:

In [22]: p - y
Out[22]: poly1d([   1,    1, -110])

poly1d的roots属性返回您期望的结果.

The roots attribute of a poly1d returns what you would expect.

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