在函数中使用if命令时的ValueError [英] ValueError when using if commands in function

问题描述

我正在创建一些函数，我可以调用use关键字来调用特定的函数，

I'm creating some functions that I can call use keywords to call out specific functions,

import scipy.integrate as integrate
import numpy as np

def HubbleParam(a, model = "None"):
    if model == "LCDM":
        Omega_L0 = 0.7
        Omega_m0 = 0.3 
        return np.sqrt( Omega_m0/a/a/a+ Omega_L0  )

    if model == "Q":
        Omega_Q0 = 0.7
        Omega_m0 = 0.3 
        return np.sqrt( Omega_m0/a/a/a + Omega_Q0/a )


def EmitterDistance(z, model = "None"):
    a = 1./(1.+z)
    if model == 'LCDM':
        integrand = 1./a/a/HubbleParam(a, model="LCDM")
        return [z , integrate.quad(integrand, a, 1.)[0] ]

    if model == "Q":
        integrand = 1/a/a/HubbleParam(a, model="Q")
        return [z, integrate.quad(inta, a, 1.)[0] ]

z = np.linspace(0.,5., 1000)

print EmitterDistance(z, model="LCDM")

尝试打印此数组时，会返回此信息，

When trying to print this array, this is returned,

Traceback (most recent call last):
  File      "/Users/alexandres/Desktop/Formation_Galaxies/Homework1/FoG_HW1.py", line 95, in <module>
    print EmitterDistance(z, model="LCDM")
  File "/Users/alexandres/Desktop/Formation_Galaxies/Homework1/FoG_HW1.py", line 87, in EmitterDistance
    return [z , integrate.quad(integrand, a, a)[0] ]
  File     "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/scipy/integrate/quadpack.py", line 315, in quad
points)
  File     "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/scipy/integrate/quadpack.py", line 364, in _quad
    if (b != Inf and a != -Inf):
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
[Finished in 0.5s with exit code 1]
[shell_cmd: python -u     "/Users/alexandres/Desktop/Formation_Galaxies/Homework1/FoG_HW1.py"]
[dir: /Users/alexandres/Desktop/Formation_Galaxies/Homework1]
[path: /usr/bin:/bin:/usr/sbin:/sbin]

或更重要的是

ValueError：The具有多个元素的数组的真值是不明确的。使用a.any（）或a.all（）

这里有什么问题？

推荐答案

在需要标量值的上下文中使用数组时会产生这种错误。它在 if 表达式中测试 a！= -Inf 。 a 和 b 这里是集成的边界点。它们应该是标量，而不是数组。但是你打电话给 quad ：

This kind of error results when you use an array in a context that expects a scalar value. It is testing a != -Inf in an if expression. a and b here are the boundary points of the integration. They should be scalars, not arrays. But you are calling quad with:

 quad(integrand, a, a)

a 这里是 a = 1 ./（1. + z）， z 是 linspace <生成的数组/ code>。

a here is a = 1./(1.+z), and z is the array produced by linspace.

integrand 也看起来有问题。它是从 a 派生的数组。相反，它应该是一个功能。带标量并返回值的东西。 HubbleParam 可能有效，或 lambda 或使用它的函数def。

integrand also looks problematic. It is array derived from a. It should, instead, be a function. Something that takes a scalar and returns a value. HubbleParam might work, or a lambda or function def using it.

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