Message 333443 - Python tracker

Message333443

Author	Petter S
Recipients	FR4NKESTI3N, Petter S, lisroach, xtreak
Date	2019-01-11.08:32:44
SpamBayes Score	-1.0
Marked as misclassified	Yes
Message-id	<1547195564.24.0.116430370553.issue35656@roundup.psfhosted.org>
In-reply-to

Content
I am of the opposite opinion. :-) > if I know roughly what the float should be why would I not want to test it for exactness? When testing algorithms, it is often the case that the answer should be mathematically exactly 2, but due to floating-point inexactness it becomes, say, 1.9999999997 in practice. If I then test for exactly 1.9999999997 the test becomes very brittle and sensitive for e.g. order of multiplications. Testing floating point numbers with a relative error is essential in many application.

Content

I am of the opposite opinion. :-) 

> if I know roughly what the float should be why would I not want to test it for exactness?

When testing algorithms, it is often the case that the answer should be mathematically exactly 2, but due to floating-point inexactness it becomes, say, 1.9999999997 in practice. If I then test for exactly 1.9999999997 the test becomes very brittle and sensitive for e.g. order of multiplications.

Testing floating point numbers with a relative error is essential in many application.

History
Date	User	Action	Args
2019-01-11 08:32:45	Petter S	set	recipients: + Petter S, lisroach, xtreak, FR4NKESTI3N
2019-01-11 08:32:44	Petter S	set	messageid: <1547195564.24.0.116430370553.issue35656@roundup.psfhosted.org>
2019-01-11 08:32:44	Petter S	link	issue35656 messages
2019-01-11 08:32:44	Petter S	create