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Re: Question: representation of uncertainties in scientific notation

• Subject: Re: Question: representation of uncertainties in scientific notation
• From: Brian McMahon <bm@xxxxxxxx>
• Date: Fri, 2 Aug 2002 10:34:58 +0100 (BST)

>    My understanding is the conventional crystallographic notation for a
> number in exponential notation is 
> 
> 	-1.2345(2) x 10^1
> 
> but my reading of section 59 in
> http://www.iucr.org/iucr-top/cif/developers/spec/cifsyntax.html 
> is that CIF uses 
> 
> 	-1.2345e1(2)
> 
> I just want to check that -1.2345(2)e1 is not valid and has never been
> intended to valid in CIF.

The *intention* is to specify one particular representation, namely
-1.2345e1(2) and *not* -1.2345(2)e1. This is making concrete the usage
implied in paragraph 5. on page 657 of Hall, Allen & Brown (1991),
Acta Cryst. A47, 655-685.

As Nick's response indicates, there are grounds for arguing in favour of
alternative representations, but it adds a little more burden to parsers. So
it is certainly interesting to see whether Brian T.'s question raises anyone
who is using the other version in practice. If not, we intend to stick with
the current single allowed format.

However, I draw your attention to the fact that the current production for
<Exponent> in the cifsyntax document generalises the Hall, Allen & Brown  
paragraph 5 to explicitly permit the following representations to be
considered as valid:

      -1.2345e1(2)
      -1.2345E1(2)
      -1.2345d1(2)
      -1.2345D1(2)
      -1.2345+1(2)
      -1.2345e+1(2)  (etc)

Again,
   (a) is anyone currently using the 'd' or '+' forms;
   (b) are there any strong views on this generalisation?

Brian

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