From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,cc4f25d878383cc X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2001-12-12 06:37:44 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!logbridge.uoregon.edu!hammer.uoregon.edu!skates!not-for-mail From: Stephen Leake Newsgroups: comp.lang.ada Subject: Re: Dimensionality Checking (Ada 20XX) Date: 12 Dec 2001 09:21:44 -0500 Organization: NASA Goddard Space Flight Center Message-ID: References: <9v37ru$cdmva$2@ID-25716.news.dfncis.de> <9v4fkq$2bl$1@mvmap66.ciw.uni-karlsruhe.de> <9v5gjl$d9cth$1@ID-25716.news.dfncis.de> <9v5pmr$ftq$1@mvmap66.ciw.uni-karlsruhe.de> <2ZxR7.35081$ER5.394136@rwcrnsc52> NNTP-Posting-Host: anarres.gsfc.nasa.gov Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: skates.gsfc.nasa.gov 1008167092 28954 128.183.220.71 (12 Dec 2001 14:24:52 GMT) X-Complaints-To: dscoggin@cne-odin.gsfc.nasa.gov NNTP-Posting-Date: 12 Dec 2001 14:24:52 GMT User-Agent: Gnus/5.0808 (Gnus v5.8.8) Emacs/20.7 Xref: archiver1.google.com comp.lang.ada:17833 Date: 2001-12-12T14:24:52+00:00 List-Id: "Mark Lundquist" writes: > "Thomas Koenig" wrote in message > news:9v5pmr$ftq$1@mvmap66.ciw.uni-karlsruhe.de... > > > > The logarithm of a unit does not have significance. > > Decibels are the logarithm of something (actually, a multiple of a > logarithm), and that something has units, e.g. (typically) sound pressure in > micropascals (a pascal is 1 N/m**2). Actually, Decibels are the log of a _ratio_ of sound pressure levels: Db = 10 log P/P_0 where P_0 is a reference sound pressure. I don't have my physics book handy (it's at home so my daughter can use it; wow!), so I don't remember what the standard reference is. > The astronomical magnitude scale is logarithmic with respect to > brightness. Again, log of a ratio, relative to some standard brightness. > pH is the negative log of the moles/L of H+. Hmm, that sounds right, but my chemistry book is at home also. > The Richter magnitude scale is logarithmic. > > Optical transmission density is logarithmic (don't know the units though). The basic point is that it is fundamentally meaningless to pass a value with non-unit dimensions to a transcendental function. All of these examples must define some standard value, take a ratio, and then take a log. Math is the language of physics, and it doesn't lie! Hmm, this is getting a bit far from Ada :). -- -- Stephe