[phenixbb] Speeding direct summation ?

Pavel Afonine pafonine at lbl.gov
Fri Nov 2 09:38:56 PDT 2018

Hi Clement,

> I have (very) high resolution data, for which direct summation method 
> seems to give significantly better map than FFT (i.e. visible hydrogen 
> vs not).

at some point we spent a lot of time experimenting with this:

Acta Cryst. (2004). A60, 19-32
On a fast calculation of structure factors at a subatomic resolution
P. V. Afonine and A. Urzhumtsev

and I can't remember seeing any significant difference in 
R-factors/maps. So.. there must be something special going on in your 
case. If you send me files I may be able to tell you what exactly is 
going on. Otherwise, if you'd like to tackle this yourself, you can 
start with changing sampling finess (resolution_factor) to something 
like 1./5 or 1/6., which will still be much faster than direct summation 
yet produce even greater match between approximations.


More information about the phenixbb mailing list