# Setting -dt and -b options in gmx trjconv **URL:** \ **Category:** User discussions\ **Tags:** analysis-tools\ **Created:** [December 30, 2021, 6:50am UTC](https://gromacs.bioexcel.eu/t/setting-dt-and-b-options-in-gmx-trjconv/3378 "2021-12-30T06:50:51Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Akki](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/akki/32/958_2.png) [@Akki](https://gromacs.bioexcel.eu/u/Akki)\ **Post date:** [December 30, 2021, 6:50am UTC](https://gromacs.bioexcel.eu/t/setting-dt-and-b-options-in-gmx-trjconv/3378/1 "2021-12-30T06:50:51Z")
GROMACS version: GROMACS modification: Yes/No Here post your question : Please clarify my doubt on How to set -dt and -b options in gmx trjconv… And what effect does it have on number of frames… Thank you ---
**Author:** ![scinikhil](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/scinikhil/32/3483_2.png) [@scinikhil](https://gromacs.bioexcel.eu/u/scinikhil)\ **Post date:** [December 30, 2021, 1:28pm UTC](https://gromacs.bioexcel.eu/t/setting-dt-and-b-options-in-gmx-trjconv/3378/2 "2021-12-30T13:28:37Z")
[https://manual.gromacs.org/documentation/2021/onlinehelp/gmx-trjconv.html](https://manual.gromacs.org/documentation/2021/onlinehelp/gmx-trjconv.html) ---
**Author:** ![Akki](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/akki/32/958_2.png) [@Akki](https://gromacs.bioexcel.eu/u/Akki)\ **Post date:** [January 3, 2022, 10:13am UTC](https://gromacs.bioexcel.eu/t/setting-dt-and-b-options-in-gmx-trjconv/3378/3 "2022-01-03T10:13:50Z")
I have checked the provided link, but still I didn’t understand on how to set these values… On what basis… Please help me with that… ---
**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\ **Post date:** [January 3, 2022, 2:42pm UTC](https://gromacs.bioexcel.eu/t/setting-dt-and-b-options-in-gmx-trjconv/3378/4 "2022-01-03T14:42:20Z")
You set whatever values you need; if you want to skip the first X ps of the trajectory, use `-b X`, and if you want to skip some frames, you can use `-dt` but `-skip` is easier to use. ---
**Author:** ![Akki](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/akki/32/958_2.png) [@Akki](https://gromacs.bioexcel.eu/u/Akki)\ **Post date:** [January 3, 2022, 4:30pm UTC](https://gromacs.bioexcel.eu/t/setting-dt-and-b-options-in-gmx-trjconv/3378/6 "2022-01-03T16:30:05Z")
But sir, Why is there a need of deleting frames… Doesn’t it affects our results?? ---
**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\ **Post date:** [January 3, 2022, 4:40pm UTC](https://gromacs.bioexcel.eu/t/setting-dt-and-b-options-in-gmx-trjconv/3378/7 "2022-01-03T16:40:58Z")
There are many reasons to shorten a trajectory or divide it into segments to do various analyses. There is no requirement to do this. ---
**Author:** ![Akki](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/akki/32/958_2.png) [@Akki](https://gromacs.bioexcel.eu/u/Akki)\ **Post date:** [January 3, 2022, 4:54pm UTC](https://gromacs.bioexcel.eu/t/setting-dt-and-b-options-in-gmx-trjconv/3378/8 "2022-01-03T16:54:59Z")
okk sir… Thank you soo much… ---
**Author:** ![Akki](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/akki/32/958_2.png) [@Akki](https://gromacs.bioexcel.eu/u/Akki)\ **Post date:** [January 3, 2022, 4:55pm UTC](https://gromacs.bioexcel.eu/t/setting-dt-and-b-options-in-gmx-trjconv/3378/9 "2022-01-03T16:55:36Z")
Can you please help me on how to build Markov state models using simulation data… ---
**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\ **Post date:** [January 3, 2022, 6:34pm UTC](https://gromacs.bioexcel.eu/t/setting-dt-and-b-options-in-gmx-trjconv/3378/10 "2022-01-03T18:34:44Z")
That’s not something GROMACS does natively. You’ll have to look into other software to build an MSM. ---
**Author:** ![Akki](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/akki/32/958_2.png) [@Akki](https://gromacs.bioexcel.eu/u/Akki)\ **Post date:** [January 4, 2022, 4:32am UTC](https://gromacs.bioexcel.eu/t/setting-dt-and-b-options-in-gmx-trjconv/3378/11 "2022-01-04T04:32:26Z")
Ya… Thank you sir… Can you please help me on how to make Force-extension curve using simulation data… ---
**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\ **Post date:** [January 4, 2022, 1:58pm UTC](https://gromacs.bioexcel.eu/t/setting-dt-and-b-options-in-gmx-trjconv/3378/12 "2022-01-04T13:58:25Z")
It would be better to start a new discussion thread if you’re asking unrelated questions. ---
**Author:** ![Akki](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/akki/32/958_2.png) [@Akki](https://gromacs.bioexcel.eu/u/Akki)\ **Post date:** [January 4, 2022, 5:12pm UTC](https://gromacs.bioexcel.eu/t/setting-dt-and-b-options-in-gmx-trjconv/3378/13 "2022-01-04T17:12:36Z")
okk sure…