Python 我收到一个警告 <RuntimeWarning: invalid value 在 sqrt>
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I am getting a warning <RuntimeWarning: invalid value encountered in sqrt>
提问by Maroof G
I am trying to run a quadratic equation in python. However, it keeps on giving me a warning
我正在尝试在 python 中运行二次方程。但是，它不断给我警告
RuntimeWarning: invalid value encountered in sqrt
Here's my code:
这是我的代码：
import numpy as np
a = 0.75 + (1.25 - 0.75)*np.random.randn(10000)
print(a)
b = 8 + (12 - 8)*np.random.randn(10000)
print(b)
c = -12 + 2*np.random.randn(10000)
print(c)
x0 = (-b - np.sqrt(b**2 - (4*a*c)))/(2 * a)
print(x0)
回答by DeepSpace
This is not 100% Python related. You can't calculate the square root of a negative number (when dealing with real numbers that is).
这不是 100% 与 Python 相关的。您无法计算负数的平方根（在处理实数时）。
You didn't take any precautions for when b**2 - (4*a*c)is a negative number.
您没有对 whenb**2 - (4*a*c)是负数采取任何预防措施。
>>> import numpy as np
>>>
>>> np.sqrt(4)
2.0
>>> np.sqrt(-4)
__main__:1: RuntimeWarning: invalid value encountered in sqrt
nan
Let's test if you have negative values:
让我们测试您是否有负值：
>>> import numpy as np
>>>
>>> a = 0.75 + (1.25 - 0.75) * np.random.randn(10000)
>>> b = 8 + (12 - 8) * np.random.randn(10000)
>>> c = -12 + 2 * np.random.randn(10000)
>>>
>>> z = b ** 2 - (4 * a * c)
>>> print len([_ for _ in z if _ < 0])
71
回答by Michael Green
If you're hoping to do complex analysis (working with imaginary numbers as defined by sqrt(-1)) you can import cmath and use cmath.sqrt(-1) instead of numpy.sqrt(-1).
如果您希望进行复杂分析（使用由 sqrt(-1) 定义的虚数），您可以导入 cmath 并使用 cmath.sqrt(-1) 而不是 numpy.sqrt(-1)。
For example, when I'm calculating the refractive index of materials from permittivity and permeability (by definition, j is involved), I'll write functions in python as such:
例如，当我根据介电常数和磁导率计算材料的折射率时（根据定义，涉及 j），我将在 python 中编写如下函数：
def n(f):
y = cmath.sqrt(mu1f(f) - j*mu2f(f)) * (e1f(f) - j*e2f(f))
return y.real
Where e1f etc. are previously defined interpolating functions, all of which are a function of incident frequency f. The y resultant is, in it of itself, a complex value, the complex index of refraction, but I'm oftentimes only interested in the real portion (the refractive index) so that is what is returned.
其中 e1f 等是先前定义的插值函数，所有这些都是入射频率 f 的函数。结果 y 本身就是一个复数值，即复折射率，但我通常只对实部（折射率）感兴趣，所以这就是返回的内容。
Hope this helps
希望这可以帮助
