# \-trestart (default 10 ps) must be divisible by -dt for useful results? **URL:** \ **Category:** User discussions\ **Created:** [October 15, 2024, 1:58pm UTC](https://gromacs.bioexcel.eu/t/trestart-default-10-ps-must-be-divisible-by-dt-for-useful-results/10345 "2024-10-15T13:58:40Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![mj.rezayani](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/mj.rezayani/32/3918_2.png) [@mj.rezayani](https://gromacs.bioexcel.eu/u/mj.rezayani)\ **Post date:** [October 15, 2024, 1:58pm UTC](https://gromacs.bioexcel.eu/t/trestart-default-10-ps-must-be-divisible-by-dt-for-useful-results/10345/1 "2024-10-15T13:58:40Z")
GROMACS version: 2024 Dear Gromacs Users: When I run `gmx msd` I face this error. I can not understand what it says. ```auto Program: gmx msd, version 2024.3 Source file: src/gromacs/trajectoryanalysis/modules/msd.cpp (line 683) Function: virtual void gmx::analysismodules::Msd::analyzeFrame(int, const t_trxframe&, t_pbc*, gmx::TrajectoryAnalysisModuleData*) Inconsistency in user input: -trestart (default 10 ps) must be divisible by -dt for useful results. For more information and tips for troubleshooting, please check the GROMACS website at https://manual.gromacs.org/current/user-guide/run-time-errors.html ``` Could you please help me with that? I think this is just for the 2024 version because I did not face this error in previous versions. ---
**Author:** ![MagnusL](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/magnusl/32/2380_2.png) [@MagnusL](https://gromacs.bioexcel.eu/u/MagnusL)\ **Post date:** [October 15, 2024, 2:24pm UTC](https://gromacs.bioexcel.eu/t/trestart-default-10-ps-must-be-divisible-by-dt-for-useful-results/10345/2 "2024-10-15T14:24:56Z")
Yes, this check ([gmx msd: throw error if -trestart is not divisible by -dt and moved check for dt\_ \> trestart (!4259) · Merge requests · GROMACS / GROMACS · GitLab](https://gitlab.com/gromacs/gromacs/-/merge_requests/4259)) was introduced in 2024.2 to fix this bug ([Unexpected results for MSD, for various -dt (#5051) · Issues · GROMACS / GROMACS · GitLab](https://gitlab.com/gromacs/gromacs/-/issues/5051)). Do you specify `-dt`? To what? What is the interval between the frames in your trajectory file? ---
**Author:** ![mj.rezayani](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/mj.rezayani/32/3918_2.png) [@mj.rezayani](https://gromacs.bioexcel.eu/u/mj.rezayani)\ **Post date:** [October 15, 2024, 2:37pm UTC](https://gromacs.bioexcel.eu/t/trestart-default-10-ps-must-be-divisible-by-dt-for-useful-results/10345/3 "2024-10-15T14:37:28Z")
Dear MagnusL, Thanks for your reply. This a part of is my .mdp file. ```auto ; Run parameters integrator = md ; leap-frog integrator nsteps = 60000000 dt = 0.0005 ; Output control nstxout = 5000 ; save coordinates every - ps nstvout = 5000 ; save velocities every - ps nstenergy = 5000 ; save energies every - ps nstlog = 5000 ; update log file every - ps ``` Actually, I don’t know how to specify -dt. I know it should be in gmx msd command but I don’t know how to specify the number. ---
**Author:** ![MagnusL](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/magnusl/32/2380_2.png) [@MagnusL](https://gromacs.bioexcel.eu/u/MagnusL)\ **Post date:** [October 15, 2024, 2:52pm UTC](https://gromacs.bioexcel.eu/t/trestart-default-10-ps-must-be-divisible-by-dt-for-useful-results/10345/4 "2024-10-15T14:52:48Z")
Then it seems like you are suffering from [gmx msd crashes when trajectory was saved too often (#4694) · Issues · GROMACS / GROMACS · GitLab](https://gitlab.com/gromacs/gromacs/-/issues/4694), which will be fixed (possibly in GROMACS 2025) by [Allow femtosecond level trajectories to be analyzed in gmx-msd (!4428) · Merge requests · GROMACS / GROMACS · GitLab](https://gitlab.com/gromacs/gromacs/-/merge_requests/4428), but it has not been merged yet. ---
**Author:** ![MagnusL](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/magnusl/32/2380_2.png) [@MagnusL](https://gromacs.bioexcel.eu/u/MagnusL)\ **Post date:** [October 15, 2024, 2:53pm UTC](https://gromacs.bioexcel.eu/t/trestart-default-10-ps-must-be-divisible-by-dt-for-useful-results/10345/5 "2024-10-15T14:53:52Z")
At a closer thought, it should not be that bug. Sorry. I’ll see if I can understand what’s the problem. ---
**Author:** ![mj.rezayani](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/mj.rezayani/32/3918_2.png) [@mj.rezayani](https://gromacs.bioexcel.eu/u/mj.rezayani)\ **Post date:** [October 15, 2024, 3:00pm UTC](https://gromacs.bioexcel.eu/t/trestart-default-10-ps-must-be-divisible-by-dt-for-useful-results/10345/6 "2024-10-15T15:00:52Z")
Thank you very much. For this .mdp file : ```auto ; Run parameters integrator = md nsteps = 60000000 dt = 0.001 ; Output control nstxout = 20000 nstvout = 20000 nstenergy = 20000 nstlog = 20000 ``` I used this command: `gmx msd -f nvt5.xtc -s nvt5.tpr -o msd.xvg -trestart 20` And, It is worked. But, I have no reason for the selection of `-trestart 20` . :-)) ---
**Author:** ![MagnusL](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/magnusl/32/2380_2.png) [@MagnusL](https://gromacs.bioexcel.eu/u/MagnusL)\ **Post date:** [October 16, 2024, 5:55am UTC](https://gromacs.bioexcel.eu/t/trestart-default-10-ps-must-be-divisible-by-dt-for-useful-results/10345/7 "2024-10-16T05:55:08Z")
In the last case it worked because `-trestart` must be divisible by `-dt` (or the time between frames. In that case you write every 20 ps, so `-trestart` cannot be \< 20. ---
**Author:** ![mj.rezayani](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/mj.rezayani/32/3918_2.png) [@mj.rezayani](https://gromacs.bioexcel.eu/u/mj.rezayani)\ **Post date:** [October 16, 2024, 10:28am UTC](https://gromacs.bioexcel.eu/t/trestart-default-10-ps-must-be-divisible-by-dt-for-useful-results/10345/8 "2024-10-16T10:28:44Z")
Dear MagnusL Thanks