From: Michael Sierchio <xhqmh@qanv.pbz>
Subject: Re: floating point comparison
Date: 1997/08/02
Date: 1997-08-02T00:00:00+00:00 [thread overview]
Message-ID: <33E3848F.5B1@qanv.pbz> (raw)
In-Reply-To: mheaney-ya023680002907972345420001@news.ni.net
Matthew Heaney wrote:
> My immediate problem is, How do I test 2 floating point numbers for equality?
Never test floating point numbers for equality! :-)
> The AQ&S states that
>
> if abs (X - Y) <= Float_T'Small
Numerical analysis is a fun discipline! For all you know, X and Y are
equal, except that you used different methods to derive them, and
they differ in one bit. Arrgh. Checking that they are within some
epsilon is proper, but deciding upon that epsilon may be hard.
There are multiple sources of error in a number: imprecision, so that
roundoff error accumulates, and the measurement limits (in the case of
a physical process) are big ones. The old physics/chem method of
retaining a fixed number of significant figures is naive at best --
Interval arithmetic may help -- you may choose to decide that two fp
nums are equal if their intervals overlap.
next prev parent reply other threads:[~1997-08-02 0:00 UTC|newest]
Thread overview: 105+ messages / expand[flat|nested] mbox.gz Atom feed top
1997-07-29 0:00 floating point comparison Matthew Heaney
1997-07-30 0:00 ` Jan Galkowski
1997-07-31 0:00 ` Don Taylor
1997-07-31 0:00 ` Russ Lyttle
1997-08-01 0:00 ` W. Wesley Groleau x4923
1997-08-02 0:00 ` Robert Dewar
1997-08-02 0:00 ` Matthew Heaney
1997-08-03 0:00 ` Robert Dewar
1997-08-04 0:00 ` W. Wesley Groleau x4923
1997-08-05 0:00 ` Jan-Christoph Puchta
1997-08-05 0:00 ` W. Wesley Groleau x4923
1997-08-05 0:00 ` Samuel Mize
1997-08-06 0:00 ` Chris L. Kuszmaul
1997-08-07 0:00 ` Dave Sparks
1997-08-08 0:00 ` Mark Eichin
1997-08-08 0:00 ` Jan-Christoph Puchta
1997-08-09 0:00 ` Robert Dewar
1997-08-10 0:00 ` Lynn Killingbeck
1997-08-08 0:00 ` Robert Dewar
[not found] ` <5sbb90$qsc@redtail.cruzio.com>
[not found] ` <5scugs$jdc$1@cnn.nas.nasa.gov>
1997-08-07 0:00 ` Robert Dewar
1997-08-08 0:00 ` Gerhard Heinzel
1997-08-08 0:00 ` Daniel Villeneuve
1997-08-08 0:00 ` schlafly
1997-08-09 0:00 ` Robert Dewar
1997-08-09 0:00 ` David Ullrich
1997-08-10 0:00 ` Robert Dewar
1997-08-16 0:00 ` Andrew V. Nesterov
1997-08-18 0:00 ` Robert Dewar
1997-08-19 0:00 ` Hans Olsson
1997-08-19 0:00 ` Jim Carr
1997-08-21 0:00 ` Christian Bau
1997-08-21 0:00 ` Jim Carr
1997-08-21 0:00 ` Robert Dewar
1997-08-22 0:00 ` Jim Carr
1997-08-22 0:00 ` Robert Dewar
1997-08-23 0:00 ` Jim Carr
1997-08-24 0:00 ` Robert Dewar
1997-08-29 0:00 ` Andrew V. Nesterov
1997-08-29 0:00 ` Robert Dewar
[not found] ` <340DF1DD.2736@iop.com>
1997-09-07 0:00 ` Get_Immediate Robert Dewar
1997-09-07 0:00 ` Get_Immediate Robert Dewar
1997-09-08 0:00 ` Get_Immediate J Giffen
[not found] ` <5u4eq6$30b$1@news.lth.se>
1997-08-29 0:00 ` floating point comparison Robert Dewar
1997-09-01 0:00 ` Chris RL Morgan
1997-09-01 0:00 ` Jim Carr
[not found] ` <checkerEFx6xI.FCM@netcom.com>
1997-09-03 0:00 ` Chris L. Kuszmaul
1997-09-05 0:00 ` Malome Khomo
1997-09-07 0:00 ` Robert Dewar
1997-09-05 0:00 ` Robert Dewar
1997-09-10 0:00 ` Jim Carr
1997-09-12 0:00 ` Robert Dewar
1997-09-15 0:00 ` James Pauley
1997-09-16 0:00 ` Robert Dewar
1997-08-23 0:00 ` W. Wesley Groleau x4923
1997-08-23 0:00 ` Robert Dewar
1997-08-30 0:00 ` Paul Eggert
1997-08-06 0:00 ` Robert Dewar
1997-08-07 0:00 ` Shmuel (Seymour J.) Metz
1997-08-08 0:00 ` Peter Shenkin
1997-08-09 0:00 ` Albert Y.C. Lai
1997-08-06 0:00 ` Robert Dewar
[not found] ` <33E8E3E1.17EA@pseserv3.fw.hac.com>
[not found] ` <5sbgpk$q0n$1@goanna.cs.rmit.edu.au>
1997-08-07 0:00 ` Robert Dewar
[not found] ` <33FE4603.1B6B@pseserv3.fw.hac.com>
1997-08-23 0:00 ` Robert Dewar
1997-08-08 0:00 ` W. Wesley Groleau x4923
1997-08-06 0:00 ` Robert Dewar
1997-08-07 0:00 ` Dr. Rex A. Dwyer
[not found] ` <33E8DFF6.6F44@pseserv3.fw.hac.com>
1997-08-07 0:00 ` Robert Dewar
[not found] ` <33EA1251.3466@link.com>
[not found] ` <33EA46CC.226@pseserv3.fw.hac.com>
1997-08-08 0:00 ` Christian Bau
1997-08-12 0:00 ` Martin Tom Brown
1997-08-23 0:00 ` W. Wesley Groleau x4923
1997-08-23 0:00 ` Robert Dewar
1997-09-05 0:00 ` Robert I. Eachus
1997-09-06 0:00 ` schlafly
1997-09-09 0:00 ` Robert Dewar
1997-09-07 0:00 ` M. J. Saltzman
1997-09-11 0:00 ` Robin Rosenberg
1997-08-07 0:00 ` Do-While Jones
1997-08-03 0:00 ` Brian Rogoff
1997-08-03 0:00 ` Robert Dewar
1997-07-30 0:00 ` Robert Dewar
1997-07-30 0:00 ` Matthew Heaney
1997-07-31 0:00 ` Jim Carr
1997-07-30 0:00 ` Matthew Heaney
1997-07-31 0:00 ` Samuel Mize
1997-07-31 0:00 ` Bob Binder (remove .mapson to email)
1997-07-31 0:00 ` Robert Dewar
1997-08-01 0:00 ` Dale Stanbrough
1997-08-04 0:00 ` Paul Eggert
1997-08-06 0:00 ` Robert Dewar
1997-08-14 0:00 ` Paul Eggert
1997-08-01 0:00 ` user
1997-08-02 0:00 ` Lynn Killingbeck
1997-08-03 0:00 ` Bob Binder (remove .mapson to email)
1997-08-03 0:00 ` Charles R. Lyttle
1997-08-03 0:00 ` Robert Dewar
1997-08-02 0:00 ` Peter L. Montgomery
1997-08-04 0:00 ` W. Wesley Groleau x4923
1997-08-05 0:00 ` Bob Binder (remove .mapson to email)
1997-07-31 0:00 ` Martin Tom Brown
1997-07-31 0:00 ` Robert Dewar
1997-08-02 0:00 ` Lynn Killingbeck
1997-07-31 0:00 ` Gerald Kasner
1997-07-31 0:00 ` Robert Dewar
1997-08-02 0:00 ` Michael Sierchio [this message]
1997-08-08 0:00 ` floating point conversions Mark Lusti
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