Python —被numpy的分段函数所迷惑 [英] Python — confused by numpy's piecewise function

问题描述

我正在尝试在Python中实现分段功能.由于我使用了numpy中的许多工具，因此我仅从中导入所有内容(即from numpy import *).我的分段函数定义为

I'm trying to implement a piecewise function in Python. Since I'm using quite a few tools from numpy, I simply import everything from it (i.e. from numpy import *). My piecewise function is defined as

LinQuad = piecewise( t, [t < 1, t >= 1], [lambda t : t, lambda t : t**2] )

这将导致错误NameError: global name 't' is not defined.我不明白为什么要定义t —毕竟，没有必要为简单的lambda函数Lin = lambda t : t定义t.在某些示例中，定义了t的域，但是我不知道函数LinQuad将在哪个值上求值.该怎么办?

which results in the error NameError: global name 't' is not defined. I don't understand why I should define t — after all, it is not necessary to define t for a simple lambda function Lin = lambda t : t. In some examples the domain of t is defined, but I don't know at which values the function LinQuad will be evaluated. What to do?

推荐答案

我不是numpy专家，但是在我看来，您似乎希望分段返回一个可以在其他地方使用的函数.那不是它的作用-它自己计算函数结果.您可能会编写一个lambda表达式，该表达式将采用任意域并返回其计算结果:

I'm no numpy expert, but it looks to me like you're expecting piecewise to return a function that you can then use elsewhere. That's not what it does - it calculates the function result itself. You could probably write a lambda expression that would take an arbitrary domain and return your calculation on it:

LinQuad = lambda x: piecewise(x, [x < 1, x >= 1], [lambda t: t, lambda t: t**2])

我不太确定在那里定义condlist布尔数组-大概是numpy特有的.

I am none too sure about defining the condlist boolean arrays there - presumably that's something specific to numpy.

或者，如果适合您的情况:

Or if appropriate to your situation:

def LinQuad(x):
   return piecewise(x, [x < 1, x >= 1], [lambda t: t, lambda t: t**2])

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