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Groups > comp.lang.python > #91230
| Date | 2015-05-25 22:09 -0700 |
|---|---|
| From | Gary Herron <gherron@digipen.edu> |
| Subject | Re: a more precise distance algorithm |
| References | <b2e66a94-7a89-4be9-bbf7-9434396cc178@googlegroups.com> <5563e453$0$12990$c3e8da3$5496439d@news.astraweb.com> <f7bd33f0-f6e0-48cd-a8ea-bdd05fcced2a@googlegroups.com> |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.49.1432617306.5151.python-list@python.org> (permalink) |
On 05/25/2015 09:13 PM, ravas wrote: > On Monday, May 25, 2015 at 8:11:25 PM UTC-7, Steven D'Aprano wrote: >> Let's compare three methods. >> ... >> which shows that: >> >> (1) It's not hard to find mismatches; >> (2) It's not obvious which of the three methods is more accurate. > Thank you; that is very helpful! > > I'm curious: what about the sqrt() function being last is detrimental? > From a point of ignorance it seems like we are just producing errors sooner, > and then multiplying them, with this alternative method. It's probably not the square root that's causing the inaccuracies. In many other cases, and probably here also, it's the summing of two numbers that have vastly different values that loses precision. A demonstration: >>> big = 100000000.0 >>> small = 0.000000001 >>> (big+small)-big # Should produce a value =small, but gives an exact zero instead. 0.0 The squaring of the two values in x*x+y*y just makes the addition even more error prone since the squares make large values even larger and small values even smaller. Gary Herron. -- Dr. Gary Herron Department of Computer Science DigiPen Institute of Technology (425) 895-4418
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a more precise distance algorithm ravas <ravas@outlook.com> - 2015-05-25 12:21 -0700
Re: a more precise distance algorithm felix <felix@epepm.cupet.cu> - 2015-05-25 16:06 -0400
Re: a more precise distance algorithm Christian Gollwitzer <auriocus@gmx.de> - 2015-05-25 22:27 +0200
Re: a more precise distance algorithm ravas <ravas@outlook.com> - 2015-05-25 14:03 -0700
Re: a more precise distance algorithm Gary Herron <gary.herron@islandtraining.com> - 2015-05-25 13:20 -0700
Re: a more precise distance algorithm ravas <ravas@outlook.com> - 2015-05-25 14:05 -0700
Re: a more precise distance algorithm Steven D'Aprano <steve@pearwood.info> - 2015-05-26 13:11 +1000
Re: a more precise distance algorithm ravas <ravas@outlook.com> - 2015-05-25 21:13 -0700
Re: a more precise distance algorithm Gary Herron <gherron@digipen.edu> - 2015-05-25 22:09 -0700
Re: a more precise distance algorithm ravas <ravas@outlook.com> - 2015-05-25 22:49 -0700
Re: a more precise distance algorithm Christian Gollwitzer <auriocus@gmx.de> - 2015-05-26 07:33 +0200
Re: a more precise distance algorithm Brian Blais <bblais@gmail.com> - 2015-05-27 14:00 -0400
Re: a more precise distance algorithm Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2015-05-27 23:03 +0100
Re: a more precise distance algorithm Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-05-27 23:04 -0400
Re: a more precise distance algorithm Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-25 22:42 -0600
Re: a more precise distance algorithm ravas <ravas@outlook.com> - 2015-05-25 21:59 -0700
Re: a more precise distance algorithm random832@fastmail.us - 2015-05-26 09:40 -0400
Re: a more precise distance algorithm random832@fastmail.us - 2015-05-26 09:51 -0400
Re: a more precise distance algorithm Robin Becker <robin@reportlab.com> - 2015-05-27 14:02 +0100
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