RE: [boost] Re: physical units library

From: Paul A. Bristow (boost_at_[hidden])
Date: 2002-10-17 14:29:15

This is still an very important need for all the science and technology areas.
It is good to see work is still going on - though IMHO it is very complicated
and far from clear how to fit all these requirements (and several others)
together.

> That having been said, in general I would prefer something a little more
> like the FermiLab approach as it seems more intuitive to me.  Namely, it is
> nice to simply be able to write:
>
> 5 * cm;

I like this too, and scientists are picky customers!

<snips>

>  but OTOH, I am currently of the mind that std::facet is an underused aspect
of the standard
> library.  IMHO the representation of kiloliters or meters cubed or m^3 or
> m**3 or m3 should be configurable via imbuing the output with a facet based
> on unitRepresentation : public std::facet.  Then, to change the output one
> can derive a class from unitRepresentation replacing "K" with "*K" or "K*"
> depending on the programmer's preference.

This sounds interesting - especially now that MSVC 7 works much better with
facets ...

> As for unit conversions, I think this, like any scientific Unit library in
> general, requires a "significant_digit" library like the one on which I am
> working.  Thus, as I have already greatly researched, converting between lb
> and force-kg (kN) would be only as accurate as either a) your source data or
> b) the conversion factor (about 7 digits IIRC).

The recently reviewed interval library and still to be re-reviewed math
constants suggest a framework for handling the uncertainty (latest trendy term
for what used to be 'experimental error' - now 'so last year'. ISO 'Guide to the
expression of Uncertainty in Measurement' ISBN 92-67-10188-9 (1995)).

I am now working on how to present intervals of math constants (which are
limited by the machine floating point precision) but the same method should be
able to be used for physical constants (where the limits are determined by
experimental uncertainty).  The interval library may be useful in propagating
uncertainty through calculations, though a useful solution will have to add the
information like degrees of freedom and distribution (square for computational
'error' - but often gaussian for measurements).

Paul

Paul A Bristow, Prizet Farmhouse, Kendal, Cumbria, LA8 8AB  UK
[phone]   Mobile [phone]
Mobile mailto:pabristow_at_[hidden]
mailto:pbristow_at_[hidden]

> -----Original Message-----
> From: boost-bounces_at_[hidden]
> [mailto:boost-bounces_at_[hidden]]On Behalf Of Jeffrey C. Jacobs
> Sent: Thursday, October 17, 2002 6:52 PM
> To: boost_at_[hidden]
> Subject: [boost] Re: physical units library
>
> Jeffrey.
>
> "vladimir josef sykora" <vladimir.sykora_at_[hidden]> wrote in message
> news:aok5bc$ne4$1_at_main.gmane.org...
> > Greetings boosters,
> > I've been working for some time now on a physical unit's library that I'd
> > like to submit to boost. It uses the concept of generating units out of
> > physical dimensions. It provides type-safety and implicit conversion
> between
> > units using operators.
> >
> [more...]