問題描述
我每天都在公司使用 Python 2.4.我使用了標準數學庫中的通用對數函數log"，當我輸入 log(2**31, 2) 時，它返回 31.000000000000004，這讓我覺得有點奇怪.
I work daily with Python 2.4 at my company. I used the versatile logarithm function 'log' from the standard math library, and when I entered log(2**31, 2) it returned 31.000000000000004, which struck me as a bit odd.
我對 2 的其他冪也做了同樣的事情，而且效果很好.我跑了 'log10(2**31)/log10(2)' 得到了 31.0 輪
I did the same thing with other powers of 2, and it worked perfectly. I ran 'log10(2**31) / log10(2)' and I got a round 31.0
我嘗試在 Python 3.0.1 中運行相同的原始函數，假設它已在更高級的版本中得到修復.
I tried running the same original function in Python 3.0.1, assuming that it was fixed in a more advanced version.
為什么會這樣?Python中的數學函數是否可能存在一些不準確之處?
Why does this happen? Is it possible that there are some inaccuracies in mathematical functions in Python?
推薦答案
這對于計算機算術來說是意料之中的.它遵循特定規則，例如 IEEE 754，可能與您所學的數學不符在學校.
This is to be expected with computer arithmetic. It is following particular rules, such as IEEE 754, that probably don't match the math you learned in school.
如果這確實很重要，請使用 Python 的 十進制類型.
If this actually matters, use Python's decimal type.
例子:
from decimal import Decimal, Context
ctx = Context(prec=20)
two = Decimal(2)
ctx.divide(ctx.power(two, Decimal(31)).ln(ctx), two.ln(ctx))
這篇關于Python中不準確的對數的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！