如何在python中提供的间隔之外使我的分段函数为零 [英] How to make my Piecewise function zero outside the provided interval in python

问题描述

这是我的代码:

    In [61]: import sympy as sp

    In [62]: x = sp.Symbol('x')

    In [63]: phi_1 = sp.Piecewise( ( (1.3-x)/0.3, 1<=x <=1.3 ))

    In [64]: phi_1.subs(x,1.2)
    Out[64]: 0.333333333333334

    In [65]: phi_1.subs(x,1.4)
    Out[65]: Piecewise()

更具体地说，我想得到零作为输入号的答案.65，因为 1.4 在区间 [1, 1.3] 之外.

More specifically, I want to get zero as an answer to the input no. 65, since 1.4 is outside the interval [1, 1.3].

推荐答案

您需要告诉 Piecewise 您希望函数在超出范围时计算为零，例如:

You need to tell Piecewise that you want the function to evaluate to zero when outside the bounds, for example:

import sympy as sp

x = sp.Symbol('x')

phi_1 = sp.Piecewise(
    (0, x < 1),
    (0, x > 1.3),
    ( (1.3-x)/0.3, True )
)

print(phi_1.subs(x,1.2)) # 0.333333333333334

print(phi_1.subs(x,1.4)) # 0

请注意，此语法适用于 0.7.1 和 0.7.6 -- 您的代码在 0.7.6 中使用复合条件"1 <=x 引发 TypeError=1.3

Note that this syntax works in 0.7.1 and 0.7.6 -- your code raises an TypeError in 0.7.6 with the "compound conditional" 1 <=x <=1.3

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