[gmx-users] Re: ci barely out of bounds

David van der Spoel spoel at xray.bmc.uu.se
Mon May 28 22:32:32 CEST 2007

Matteo Guglielmi wrote:
> David van der Spoel wrote:
>> chris.neale at utoronto.ca wrote:
>>> This email refers to my original posts on this topic:
>>> http://www.gromacs.org/pipermail/gmx-users/2006-October/024154.html
>>> http://www.gromacs.org/pipermail/gmx-users/2006-October/024333.html
>>> I have previously posted some of this information to somebody else's
>>> bugzilla post #109 including a possible workaround
>>> http://bugzilla.gromacs.org/show_bug.cgi?id=109
>>> I have compiled my gromacs always using one of the gcc3.3* distros. I
>>> didn't do anything fancy, just the usual configure,make,make install.
>>> I did have trouble with a gromacs version compiled using a gcc4*
>>> distro and somebody on this user list assisted me in determining that
>>> I should just roll back my gcc verison. I run on all sorts of
>>> computers, opterons and intel chips, 32 and 64 bit, and this
>>> particular ci problem is the same for me on all of them.
>>> Matteo, I want to be sure that we are on the same page here: your ci
>>> is just *barely* out of bounds right? This is a different problem
>>> than when your ci is a huge negative number. In that case you have
>>> some other problem and your system is exploding.
>>> There is one test and one workaround included in my bugzilla post.
>>> The test is to recompile gromacs with the -DEBUG_PBC flag and see if
>>> the problem still occurs. For me this solved the problem (although
>>> gromacs runs much slower so it is not a great workaround). The
>>> solution was to remake my system with a few more or a few less waters
>>> so that the number of grids wasn't changing as the volume of the box
>>> fluctuates (slightly) during constant pressure simulations.
>>> I here include the text that I added to that bugzilla post:
>>> Did you try with a version of mdrun that was compiled with -DEBUG_PBC ?
>>> I have some runs that reliably (but stochastically) give errors about
>>> an atom
>>> being found in a grid just one block outside of the expected boundary
>>> only in
>>> parallel runs, and often other nodes have log files that indicate
>>> that they have
>>> just updated the grid size (constant pressure simulation). This error
>>> disappears
>>> when I run with a -DEBUG_PBC version. My assumption here is that
>>> there is some
>>> non-blocking MPI communication that is not getting through in time. The
>>> -DEBUG_PBC version spends a lot of time checking some things and
>>> although it
>>> never reports having found some problem, I assume that a side-effect
>>> of these
>>> extra calculations is to slow things down enough at the proper stage
>>> so that the
>>> MPI message gets through. I have solved my problem by adjusting my
>>> simulation
>>> cell so that it doesn't fall close to the grid boundaries. Perhaps
>>> you are
>>> experiencing some analogous problem?
>>> Quoting Matteo Guglielmi <matteo.guglielmi at epfl.ch>:
>>>> Hello Chris,
>>>> I have the same problem with gromacs and did not understand
>>>> what's going wrong yet.
>>>> I did not try to run a serial job (as you did) but all my 7 simulations
>>>> (6 solvated pores in membranes + 1 protein in water... all of them
>>>> with positional restrains - double precision) keep crashing in the
>>>> same way.
>>>> Did you finally understand why they do crash (in parallel)?
>>>> How did you compile gromacs?
>>>> I used the intel copilers (ifort icc icpc 9.1 series) whith the
>>>> following optimization flags: -O3 -unroll -axT.
>>>> I've also tried the 8.0 series but no chance to get rid of the problem.
>>>> I'm running on woodcrest (xeon cpu 5140 2.33GHz) and xeon cpu
>>>> 3.06GHz.
>>>> Thanks for your attention,
>>>> MG
>> Do you use pressure coupling? In principle that can cause problems
>> when combined with position restraints. Further once again, please try
>> to reproduce the problem with gcc as well. If this is related to
>> bugzilla 109 as Chris suggests then please let's continue the
>> discussion there.
> Yes I do (anysotropic pressure).
> I got the same problem with the same system using a compiled version  of
> gromacs
> with gcc 3.4.6.
> So, in my case, doesn't matter which compiler I do use to compile gromacs
> (either Intel series 9.1 or gcc 3.4.6), I always get the same error
> right after
> the "update" of the Grid size.
> ....
> step 282180, will finish at Tue May 29 15:57:31 2007
> step 282190, will finish at Tue May 29 15:57:32 2007
> -------------------------------------------------------
> Program mdrun_mpi, VERSION 3.3.1
> Source code file: nsgrid.c, line: 226
> Range checking error:
> Explanation: During neighborsearching, we assign each particle to a grid
> based on its coordinates. If your system contains collisions or parameter
> errors that give particles very high velocities you might end up with some
> coordinates being +-Infinity or NaN (not-a-number). Obviously, we cannot
> put these on a grid, so this is usually where we detect those errors.
> Make sure your system is properly energy-minimized and that the potential
> energy seems reasonable before trying again.
> Variable ci has value 1472. It should have been within [ 0 .. 1440 ]
> Please report this to the mailing list (gmx-users at gromacs.org)
> -------------------------------------------------------
> "BioBeat is Not Available In Regular Shops" (P.J. Meulenhoff)
> Looking forward to have a solution,
> thanks to all of you,
> MG.
If this is reproducible as you say it is then please save your energy 
file at each step and plot the box as a function of time. Most likely it 
is exploding gently. This is most likely caused by the combination of 
position restraints and pressure coupling. Therefore it would be good to 
turn off on. I would suggest starting with posres and no pressure 
coupling, and once that equilibrates turn on pressure coupling with a 
long tau_p (e.g. 5 ps).

David van der Spoel, PhD, Assoc. Prof., Molecular Biophysics group,
Dept. of Cell and Molecular Biology, Uppsala University.
Husargatan 3, Box 596,  	75124 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://folding.bmc.uu.se

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