Discussion List Archives

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Expressions for R factors

  • To: Multiple recipients of list <coredmg@iucr.org>
  • Subject: Re: Expressions for R factors
  • From: "George M. Sheldrick" <gsheldr@shelx.uni-ac.gwdg.de>
  • Date: Fri, 4 Sep 1998 14:39:38 +0100 (BST)
Dear Brian

My programs have always used Y(obs) in the denominator, so either (a) it
is a typo in the dictionary, or (b) the majority of the CIFs in the Acta
database are wrong. Which would you prefer ?

Best wishes, George

========================================================================

Brian McMahon wrote:
> 
> John Bollinger at Indiana writes:
> 
> > With regard to _refine_ls_wR_factor_*: it seems unusual to me that the
> > sum in the denominator is over Y(calc) instead of over Y(obs).  Is this
> > intentional, and if so, can you refer me to any literature about why this
> > particular usage is to be preferred?  I have never run into it before, and I
> > shall have to make special provisions to get my software to calculate it.  I
> > see that this formula appears in the version 2.0.1 dictionary as well, but
> > that does not invalidate the question.
> 
> For example, the definition of _refine_ls_wR_factor_all is
> 
>                     ( sum | w | Y(obs) - Y(calc) |^2^ | )^1/2^
>                wR = ( --------------------------------- )
>                     (         sum | w Y(calc)^2^ |      )
> 
> as against the definition for _refine_ls_R_factor_gt, which is
> 
>                    sum | F(obs) - F(calc) |
>                R = ------------------------
>                          sum | F(obs) |
> 
> I note that the original definition for _refine_ls_wR_factor_ in version 1.0
> of the Core read
> 
>                wR = [sum(w|Ym-Yc|^2^) / sum(wYm^2^)]^1/2^
> 
> Have we simply introduced a typo into later versions?
> 
> Brian

[Send comment to list secretary]
[Reply to list (subscribers only)]