Grouping by units over add - progress, and a couple questions

hi,

On Fri, May 20, 2005 at 06:57:55AM -0700, C Y wrote:
> 
> --- Albert Reiner  wrote:
> > [C Y , Thu, 19 May 2005 18:40:13 -0700 (PDT)]:
> > > In general, it is meaningless to pose an expressin a^b where b is a
> > > quantity with units.
> > 
> > Not sure: In any book on liquid state physics you are likely to find
> > expressions like rho*log(rho), rho being of dimension 1/volume. 
> > Which is, of course, equivalent to log(rho^rho).  It may seem
> > meaningless, but that is only because some not very interesting 
> > quantities like, e.g., -rho*log(...) with ... of appropriate 
> > dimensions are often left out.
> 
> Well, I guess the question becomes different forms of the same issue -
> what units does rho*log(rho) have?  I have no idea what the log of a
> unit means physically.  Unless I do understand it it would most likely
> be worse than useless for me to attempt to program Maxima to handle it.

you might want to take a look at NIST SP-330 technical note on 
"The International System of Units", in p. 26, footnote to table
6, you can read that there are two *non-SI units accepted for use
with IS* called `neper' (Np) and `bel' (B),

-Both are used to express logarithmic quantities,
-The neper is coherent with the SI, but is not yet accepted as an SI unit
-The bel and the decibel, dB, are related to the neper

I guess you could use both to handle the log case in the units package.


Miquel

-- 
Miquel E Cabanas ------------------------------------------------------
SeRMN, Universitat Autonoma de Barcelona (Miquel.Cabanas@uab.es)
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