-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Marat Khalili Sent: 15 July 2007 07:36 To: boost@lists.boost.org Subject: Re: [boost] [rfc] Inexact quantities arithmetics
Paul A Bristow wrote:
The word error gives off some very wrong vibes, and I would strongly urge you to change to using uncertainty instead of error, despite the historial use of the word error. It *really, really* isn't an error - it is a interval of (un-)certainty.
What do you think about 'uncertainty_interval_half_width'?
It could be - but that makes all sorts of assumptions about distribution, normality? 95% confidence? ... so I think you want a more vague (and shorter!) name.
Seriously I wanted to call it 'deviation' first, but opted for shorter identifier; same number of letters as in 'value' is additional bonus, makes code more symmetrical. BTW shouldn't 'value' be called average, mean or expectancy?
Well it might be, but if there is only one exact value 2 +- 0, and you might consider it 'most likely' so again I eventually favoured a vague term like value.
I thought it is still colloquially being called 'error',
You are quite right - but I strongly advise that this is out-dated.
but I'll think about it. Some help from English-speaking folks will be appreciated.
I *really* am English-speaking! - unlike Boost's many American-English speakers ;-)
You should also see
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/29189/1/95-0368.pdf
Yes, this one looks very much like one I'm thinking about. As a work of a government employee his code must be free, shouldn't it?
I have assumed so.
and FWIW some of my comments some years ago
Is it open-source?
It isn't in a state where I would want anyone else to see it with my name on it ;-((
My uncertain class has a value, standard deviation, degrees of freedom, and 16 uncertainty type flags - square, triangular, gaussian, exact etc
This fits into 128 bits, so only doubling the space required to store a 'value'.
I also felt it was vital to store the degrees of freedom with the value and uncertainty, and I also added some other bits of information like quantization (from A/D conversion), exact values, where the uncertainty estimate came from ...
This looks too heavy for me, it was tuned for some specific task, right?
Not really, I was trying to cater for ALL types of physical measurement, from astronomy to social science.
Generally, adding or substracting two lognormal values produces god-knows-what. Either you keep the whole (joint!) distribution or nothing.
True - but I felt there was value in recording where the uncertainty estimates came from - repeated (with how many) measurements, some other estimating method, A/D conversion quantisation, round-off from number of significant digits... But I also wanted to achieve the compile-time checking of units, now a Boost library, and get output nice, including the 'right' number of significant digits (from the uncertainty). This is more that I can chew at present ;-) Though it still seems a reasonable enough requirement. Paul PS I recall some New Zealand programmers work on this, but can't find a reference immediately. --- Paul A Bristow Prizet Farmhouse, Kendal, Cumbria UK LA8 8AB +44 1539561830 & SMS, Mobile +44 7714 330204 & SMS pbristow@hetp.u-net.com