如何在python中提供的间隔之外使我的Piecewise函数为零

Question

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,我希望得到零作为输入no的答案.65,因为1.4在区间[1,1.3]之外.

Answer 1

您需要告诉Piecewise您希望函数在超出边界时评估为零,例如:

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TypeError使用"复合条件" 提高0.7.61 <=x <=1.3