[英]Floating point precision in Python
I have written this function in python: 我在python中编写了这个函数 :
import math
def radical(a, b, k):
return (1-((a**2-b**2)/a**2)*(math.sin(math.pi*(2*k-1)/180))**2)**.5
def f(a, b):
sigma = 0
for k in range(1,180/4):
sigma = sigma + radical(a, b, k)
return 8*a*math.sin(math.pi/180)*sigma
print f(25.,35.)
When I calculate this function in Wolphramapha and Maple I will get 189.797 but with python I will get 184.91089913 What is the problem in my program? 当我在Wolphramapha和Maple中计算这个函数时,我会得到189.797但是使用python 我会得到184.91089913我的程序有什么问题?
You are off by one. 你是一个人。 The
range
method excludes the end point. range
方法排除终点。 Try adding one: 尝试添加一个:
for k in range(1,180/4 + 1):
Result: 189.797208409 结果: 189.797208409
Well, first of all, python assumes integer division, so there is some serious round off in this code. 好吧,首先,python假设整数除法,所以在这段代码中有一些严重的舍入。 I believe there is an import in division for this.
我认为这有分歧。 Also, Here is some information on python's floating point arithmetic issues/problems:
另外,这里有一些关于python的浮点运算问题/问题的信息:
http://docs.python.org/2/tutorial/floatingpoint.html http://docs.python.org/2/tutorial/floatingpoint.html
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