[phenixbb] Speeding direct summation ?

Tim Gruene tim.gruene at psi.ch
Fri Nov 2 09:19:17 PDT 2018

Dear Clement,

as far as I understand, SHELXL is compiled against the Intel FFT
library. Before, SHELXL used direct summation. If there was any
noticeable difference, I am sure George Sheldrich would not have taken
this step, as he would have had to expect a flood of complaints. My
guess is that the difference is not because of the difference between

Best regards,

On 11/02/2018 05:01 PM, Clement Degut wrote:
> Hi,
> 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).
> My main problem is that refinement got from quite slow, to barely not
> really possible to handle slow.
> I have 2 question from that :
> Am I looking at an artifact ? Meaning should at this resolution (0.84A
> for CC1/2 at 30% and good overall statistics) see extreme difference
> between map quality with direct summation vs FFT ?
> And if yes, can I speed the process compiling phenix with openMP on our
> cluster ? Or shoul I just become patient ?
> Many thanks
> Clément
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Paul Scherrer Institut
Tim Gruene
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Forschungsstrasse 111
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