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From: pmontgom@sdcrdcf.UUCP (Peter Montgomery)
Newsgroups: comp.bugs.4bsd,sci.math.symbolic
Subject: Bug in bc square root routine
Message-ID: <4534@sdcrdcf.UUCP>
Date: Sun, 26-Apr-87 19:05:20 EDT
Article-I.D.: sdcrdcf.4534
Posted: Sun Apr 26 19:05:20 1987
Date-Received: Mon, 27-Apr-87 03:44:57 EDT
Reply-To: pmontgom@sdcrdcf.UUCP (Peter Montgomery)
Distribution: world
Organization: UNISYS, Santa Monica
Lines: 25
Xref: mnetor comp.bugs.4bsd:328 sci.math.symbolic:69


	The following bc program prints (comments added by me)

999999996999999999700000000001          (b = actual square root)
999999994000000008400000001802000000083999999999400000000001   (c = square)
999999996999999999699950000000          (d = computed square root)
50000001                                (b-d = difference)

        The problem exists both on a VAX 780 using 4.2bsd and on a SUN
2/170 using SUN release 3.0.

a = 10^10
b = 1 - 30*a - 30*a^2 + a^3
c = b^2
d = sqrt(c)
b
c
d
b-d
quit
-- 
	Peter Montgomery     {aero,allegra,bmcg,burdvax,hplabs,ihnp4,
			      psivax,randvax,sdcsvax,trwrb}!sdcrdcf!pmontgom

Don't blame me for the crowded freeways - I don't drive.