X-Authentication-Warning: delorie.com: mail set sender to geda-user-bounces using -f X-Recipient: geda-user AT delorie DOT com X-TCPREMOTEIP: 63.119.35.194 X-Authenticated-UID: jpd AT noqsi DOT com Content-Type: multipart/signed; boundary="Apple-Mail=_BAE2E6B6-C4E2-45DC-A548-454C4984C9C2"; protocol="application/pgp-signature"; micalg=pgp-sha512 Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Subject: Re: [geda-user] Re: some more geometry module tweaks (sorry, wall of text) X-Pgp-Agent: GPGMail 2.5.2 From: John Doty In-Reply-To: Date: Wed, 6 Jan 2016 19:47:56 -0500 Message-Id: <8985B557-CC87-48A0-A745-298A501945F0@noqsi.com> References: To: geda-user AT delorie DOT com X-Mailer: Apple Mail (2.1878.6) Reply-To: geda-user AT delorie DOT com Errors-To: nobody AT delorie DOT com X-Mailing-List: geda-user AT delorie DOT com X-Unsubscribes-To: listserv AT delorie DOT com Precedence: bulk --Apple-Mail=_BAE2E6B6-C4E2-45DC-A548-454C4984C9C2 Content-Type: multipart/alternative; boundary="Apple-Mail=_D6B152C3-A5F2-402E-8ABA-B3F13C882AC9" --Apple-Mail=_D6B152C3-A5F2-402E-8ABA-B3F13C882AC9 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=windows-1252 On Jan 6, 2016, at 7:29 PM, Britton Kerin (britton DOT kerin AT gmail DOT com) [via = geda-user AT delorie DOT com] wrote: > Yeah DJ hinted at this as well. My knee-jerk reaction is to use an = even winder type for the internal floating point representation. Short = of arbitrary precision there's no way to support arbitrary intermediate = results, but if you can count bye ones all the way to a squared value = that would seem to cover all the simple geometrical calculations we're = interested in. Things like hypot() help, but I admit I don't fully = understand exactly how much. They certainly keep the numbers smaller = and thereby prevent overflow, but I don't fully understand the = consequences for intermediate results outside the range where the float = can represent all integers. This particular calculation is numerically stable, even if written as = sqrt(x*x+y*y). It can=92t generally be perfect, but it=92s not the kind = of thing that sends numerical analysts into cold sweats. John Doty Noqsi Aerospace, Ltd. http://www.noqsi.com/ jpd AT noqsi DOT com --Apple-Mail=_D6B152C3-A5F2-402E-8ABA-B3F13C882AC9 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=windows-1252
On Jan 6, 2016, at 7:29 PM, Britton = Kerin (britton DOT kerin AT gmail DOT com) = [via geda-user AT delorie DOT com] = <geda-user AT delorie DOT com>= wrote:

Yeah = DJ hinted at this as well.  My knee-jerk reaction is to use an even = winder type for the internal floating point representation.  Short = of arbitrary precision there's no way to support arbitrary intermediate = results, but if you can count bye ones all the way to a squared value = that would seem to cover all the simple geometrical calculations we're = interested in.  Things like hypot() help, but I admit I don't fully = understand exactly how much.  They certainly keep the numbers = smaller and thereby prevent overflow, but I don't fully understand the = consequences for intermediate results outside the range where the float = can represent all integers.

This = particular calculation is numerically stable, even if written as = sqrt(x*x+y*y). It can=92t generally be perfect, but it=92s not the kind = of thing that sends numerical analysts into cold sweats.

John Doty              Noqsi = Aerospace, Ltd.

http://www.noqsi.com/

jpd AT noqsi DOT com

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