Re: [boost] Re: Re: Physical quantities

From: Kevin Lynch (krlynch_at_[hidden])
Date: 2004-01-12 15:15:07

Andy Little wrote:
> "Kevin Lynch" <krlynch_at_[hidden]> wrote in message
> news:3FFF1505.8010709_at_bu.edu...
> 
> [snipped]
> 

snipped the parts about what I need in a units library.

> I have 2 questions
> 
> 1) What is your knowledge of C++?

That's sort of an open ended question, but for what it's worth  :-)

I'm a practicing particle physicist, and I do lots of programming for MC 
modeling of our experiment, straight numerical calculations of designs, 
analysis of large data sets, hardware data acquisition code, etc. etc. 
etc.   I do most of this work in compiled C/C++/Fortran, and it is all 
highly numerical, and in a dialect of interpreted C/C++ that doesn't 
really understand templates.

In all of these cases, a dimensions/unit framework that does NOT allow 
implementation of user defined dimensions and units would be useless to 
me personally.  I don't think that I use SI or even CGS anywhere within 
my code: I use a mix of non-dimensionalized calculations and "natural" 
physical units.

Which sure doesn't answer the question you asked, but since I don't know 
how to answer the question asked .....

> 
> 2) Do you have any example calculations we might consider?

Probably nothing I could show, at least without some substantial work 
:-)   for two reasons:

1) I'm stuck using large frameworks for the MC work that I am not going 
to retrofit to use a units framework, and most of that code wouldn't 
make any sense except in the context of the framework.
2) Most of the other design calculations I do are formulated in 
"non-dimensionalized" form, so that I don't have to worry about units 
and numerical scaling issues :-)

Let me think about it some more, and see if I can find some time to put 
something together....

> 
> from the point of view of...
> Is the time the program takes to calculate important.

My code is either done running in less time that it takes to compile 
(short code that would only benefit from nearly zero compile time 
overhead) or already runs for hundreds of hours (and hence would want a 
zero runtime overhead, a far more important constraint for those 
applications where I would consider using the units framework).

 > Is huge accuracy important.

Numerical accuracy (which I assume you are talking about ... an 
inaccurate dimensional analysis framework would hardly be useful :-)  is 
certainly not in the purview of the DA/units framework ... that has more 
to do with the selection of algorithms, rescaling techniques, and 
underlying numerical types.....

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