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Message-ID: <500313AB.80506@t-online.de>
Date: Sun, 15 Jul 2012 21:02:03 +0200
From: Albert Graef <Dr.Gr...@t-online.de>
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To: pure-lang@googlegroups.com
Subject: Re: [pure-lang] pure and units of measure
References: <5000093A.4070606@gmail.com> <500173B5.3080805@t-online.de>
In-Reply-To: <500173B5.3080805@t-online.de>
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On 07/14/2012 03:27 PM, Albert Graef wrote:
> This is an interesting problem. :) As an alternative to Jim's approach,
> it can be viewed as a kind of algebraic simplication system and thus
> solved with symbolic rules. I've cobbled together a quick and dirty
> solution along these lines, which converts arbitrary units to the
> standard (SI) ones.

Here's an updated version of the script, which confines the
normalization to local rule sets
(http://docs.pure-lang.googlecode.com/hg/purelib.html#reduce). I think
that this design is preferable because it doesn't interfere with the
global arithmetics, and it also allows to give a better definition of
the 'as' conversion operator. The downside is that you'll have to
explicitly call a function 'si' to do the normalization now. For instance:

  > si (1*feet^3/minutes+1*gallons/seconds);
  0.0042573592272*meters^3*seconds^(-1)
  > ans as liters/minutes;
  255.441000762531*liters*minutes^(-1)
  > si ans;
  0.00425735001270885*meters^3*seconds^(-1)
  > ans as inches^3/hours;
  935277.192856837*inches^3*hours^(-1)

I also added a few more units, e.g.:

  > si (1*yards^2);
  0.83612736*meters^2
  > ans as inches^2;
  1295.99999999099*inches^2
  > 30*celsius as fahrenheit;
  86.0000000030605*fahrenheit

Well, obviously the numeric solver used by 'as' still needs to be
improved, I'm leaving that as an exercise. ;-) But other than that it
seems to work pretty well, and adding more units should be a piece of
cake now.

Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr.Gr...@t-online.de, a...@muwiinfa.geschichte.uni-mainz.de
WWW:    http://www.musikinformatik.uni-mainz.de/ag



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