[Python-ideas] PEP 485: A Function for testing approximate equality (original) (raw)

Steven D'Aprano steve at pearwood.info
Fri Feb 6 06:10:41 CET 2015

On Thu, Feb 05, 2015 at 09:53:49PM -0600, Ron Adam wrote:

I prefer the weak version myself. Because if you graph the result of True values for reltolerance=1. You get a graph where all like signed numbers are close. A tolerance of .5 gives a graph of the fifty percent of middle like signed numbers. And you can think of it as a percentage of the larger value. Which tends to be easier than thinking about percent increase.

I'm afraid I don't understand this description.

Also this recommends using this method.

http://c-faq.com/fp/fpequal.html

You stopped reading too soon:

[quote] Doug Gwyn suggests using the following ``relative difference'' function. It returns the relative difference of two real numbers: 0.0 if they are exactly the same, otherwise the ratio of the difference to the larger of the two. [end quote]

Anyone got a copy of Knuth handy and check the reference given above?

Knuth Sec. 4.2.2 pp. 217-8

I'd like to know what he has to say.

-- Steve

More information about the Python-ideas mailing list