[gmx-developers] Question on P-LINCS

[Anton Feenstra]

On 05/02/13 17:40, risueno at physik.hu-berlin.de wrote:
> Dear Gromacs developers
>
> In the P-LINCS paper (http://pubs.acs.org/doi/abs/10.1021/ct700200b) it is
> stated that P-LINCS can constrain bond angles. However, in the Gromacs
> manual (http://www.gromacs.org/Documentation/Manual, page 181), I find
> that P-LINCS is used when there is domain decomposition, but that it
> "should not be used with coupled angle constraints". So I wonder, is it
> possible to use P-LINCS with bond angle constraints? If not, why?

The key word here is 'coupled'. P-LINCS works with angle constraints, 
but not with *coupled* angle constraints. The reason is that the 
approximation for the matrix inversion assumes a sparse constraints 
matrix. Having coupled angle constraints breaks this sparsity 
assumption. (FYI, coupled angle constriants means one has, e.g. four 
atoms with 5 constraints; three for the bonds (like, i-j, j-k and k-l) 
and two for the angles (i-k and j-l)).

> In addition, I would like to ask what is the maximum number of cores for
> an efficient scalling in the parallel run of P-LINCS (perhaps there exists
> some benchmark as a function of the total number of constraints).

I don't know that. Berk is the (P-)LINCS expert.

-- 
Groetjes,

Anton
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|  _   _  ___,| K. Anton Feenstra                                     |
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