[gmx-developers] Nr of graph edges per atom and distance restraints

[Berk Hess]

David van der Spoel wrote:

> hessb at mpip-mainz.mpg.de wrote:
>
>>> Juergen Haas wrote:
>>>
>>>>> To get things right,
>>>>> you are using only distance restraints, no orientation restraints
>>>>> and you get a segfault around line 166 or orires.c, not disre.c ??
>>>>
>>>> in that case I forgot to switch off orires...:(
>>>> to wrap it up: the segfault seems to have been linked to fftw commands
>>>> and it
>>>> turned out that I overlooked a trivial error: the lam/fftw environment
>>>> on my
>>>> newly installed machine was broken.
>>>> Fixing that solved all problems and I could use the suggested hack of
>>>> increasing g->maxedge.
>>>>
>>>> Thanks!
>>>> Juergen
>>>>
>>> To finally fix the bugzilla 66, which number of did you use instead 
>>> of 4
>>> on line 229 of mshift.c?
>>
>>
>> This is not relevant.
>> The code is quite small and puts only the chemical bonds in the graph
>> for interactions within three bonds.
>> But one can define as many long-range distance restraints as one likes.
>> Therefore there is not limit to the number of graph edges.
>>
>>> Alternatively, the condition & IF_CHEMBOND on line 201 could be 
>>> replaced
>>> by & IF_BOND
>>
>>
>> This does not help.
>
>
> I think it will because then distance restraints are included, now 
> only true chemical bonds are, and then the number will be determined 
> dynamically.
>
Ah, right.
But we don't want that as a general solution,
since that could cost a lot of extra allocation and might hurt cache 
performance.

A solution for distance restraints would be to add tp==F_DISRES.
But there was recently also someone with too mant harmonic bonds...
So we should think of a robust solution.

I just looked into the code and since there is g->nedge,
we could first just count everything, then fill the graph as is done now,
then shrink the array while resetting the g->edge pointers
and realloc.

Berk.