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From: firth@sei.cmu.edu.UUCP
Newsgroups: comp.lang.c
Subject: Re: C and Floating Point
Message-ID: <901@aw.sei.cmu.edu.sei.cmu.edu>
Date: Wed, 8-Apr-87 16:37:08 EST
Article-I.D.: aw.901
Posted: Wed Apr  8 16:37:08 1987
Date-Received: Sat, 18-Apr-87 03:09:50 EST
References: <15958@sun.uucp> <5716@brl-smoke.ARPA> <14681@cca.CCA.COM> <1163@drivax.UUCP> <14813@cca.CCA.COM>
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Keywords: C Fortran Floating Point

In article <14813@cca.CCA.COM> g-rh@CCA.UUCP (Richard Harter) writes:
(brief excerpt)
>... Given that we have arranged things so that convergence
>is forced, i.e. so that are guaranteed to reach a point such that,
>for some n,
>
>	x[n+1] = x[n] + delta[n] = x[n],
>
>what is the proper way to test for this, if the calculations are
>being done in floating point?

I would suggest

	abs(delta[n]/x[n]) <= eps

(omit the abs if feasible).  This gives the compiler least chance
to screw you.  If you have some way to relate 'eps' to the machine
precision, even better.