[cctbxbb] convert an arbitrary point to one inside the asymmetric unit

[Gabor Bunkoczi]

Dear Engelbert,

you can use the asu_mappings objects to compute this (there may be
something more suitable for regular grids). Here is a link to a tutorial
written by Ralf Grosse-Kunstleve, where this is explained:

http://cci.lbl.gov/publications/download/iucrcompcomm_aug2004.pdf

BW, Gabor


On Mon, Nov 21, 2016 at 12:47 PM, Tijskens Engelbert <
Engelbert.Tijskens at uantwerpen.be> wrote:

> Hi,
>
> I am an experienced C++ and Python programmer, but new to cctbx.
>
> Can any tell me if there is an algorithm in cctbx available  to convert an
> arbritrary point in direct space to the corresponding point in the
> asymmetric unit of a given space group? i can figure out how to convert it
> to the corresponding point in the unit cell at the origin, but from there
> to the asymmetric unit is unclear to me.
>
> I found the brick class which gives me the assymmetric unit
> from cctbx import crystal,sgtbx
>
> if __name__=='__main__':
>     crystal_symmetry = crystal.symmetry( unit_cell=(3.5093,3.5093,3.5093,
> 90,90,90)
>                                        , space_group_symbol="229" # = "I
> m -3 m"
>                                        )
>     sg = crystal_symmetry.space_group()
>     brick = sgtbx.brick( sg.type() )
>     print brick
>
> I also found cctbx::sgtbx::asu and the classes therein, but they are
> largely undocumented.
>
> For the interested, this is the problem i want to solve:
> I have a (scalar) physical property P(r), depending on spatial position,
> presented as a 3D array on a regular grid over the unit cell (space group
> is known). I need to integrate P(r)*f(r), f(r) being an arbitrary function
> over a region of direct space, which typically comprises several unit
> cells. In order to reduce the memory footprint of the P array, i would like
> to restrict it to the space group’s asymmetric unit.
>
> All help is greatly appreciated.
> kindest regards,
>
> Dr [Engel]bert Tijskens
> HPC Analyst/Consultant
>
> Flemish Supercomputer Center vscentrum.be
> HPC core facility CalcUA uantwerp.be/calcua
> Computational mathematics www.uantwerpen.be/en/rg/cma
>
> University of Antwerp
> Middelheimlaan1 G.309, B-2020 Antwerp, Belgium
>
> engelbert.tijskens at uantwerpen.be
> ++32 3 265 3879
>
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>
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