[gmx-developers] What is the function of 'dd_collect_state' used to ?

[Mark Abraham]

On 22/03/2011 8:15 PM, Yukun Wang wrote:
> I don't know if there is a function in Gromacs that it can get and 
> change a specific group atom's local information,for example data in 
> the t_state data structure , when given a group, which is defined and 
> included by command of grompp -n option.
> So I can call this function in the master node and couple severial 
> simulations simultaneously .

Data structures exist that contain this information, but it's not in one 
usable place. Each processor knows which atoms are local to it, but I 
don't think they all know which processor has each atom. Use the 
collect_state functionality to prove your concept, and if you need extra 
performance, think about doing the weeks of work for implementing 
something much harder but a little bit faster.

Mark

> 2011/3/22 David van der Spoel <spoel at xray.bmc.uu.se 
> <mailto:spoel at xray.bmc.uu.se>>
>
>     On 2011-03-22 04.42, Mark Abraham wrote:
>
>         On 22/03/2011 2:38 PM, Yukun Wang wrote:
>
>             Hi
>             What is the function of 'dd_collect_state' used to ?
>
>
>         It collects the state of the simulation system, which was
>         distributed
>         across the parallel nodes, into a single structure.
>
>             In the md.c there is a function as:
>             dd_collect_state(cr->dd,state,state_global)
>             I don't know what' the mean of it,and where was it defined.
>
>             I want to realize a work by gromacs, that there are several
>             simulations which coulped weakly only by exchanging position
>             information of a group of atoms for every n steps, and for
>             each
>             simulation I want to run parallelly. So the trouble is
>             coming for each
>             simulation with domain decomposition parallelizing that
>             this group of
>             atoms would be distributed in different node.
>             How can I get those data from different nodes in the
>             running time? If
>             I put the self-written coulping code in the master node
>             for each
>             simulation how I do this data gathering job?
>
>
>         Either you need to collect on the master node and communicate
>         between
>         them before redistributing, or write complex (but ultimately more
>         scalable) code to communicate between all the processors. The REMD
>         implementation should be a good model for the former.
>
>     Indeed, or the more general -multi option.
>
>         Mark
>
>
>
>     -- 
>     David van der Spoel, Ph.D., Professor of Biology
>     Dept. of Cell & Molec. Biol., Uppsala University.
>     Box 596, 75124 Uppsala, Sweden. Phone:  +46184714205.
>     spoel at xray.bmc.uu.se <mailto:spoel at xray.bmc.uu.se>
>     http://folding.bmc.uu.se
>
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