# Colvar output force and work

**URL:** <https://gromacs.bioexcel.eu/t/colvar-output-force-and-work/3191>\
**Category:** User discussions\
**Tags:** colvars\
**Created:** [November 23, 2021, 5:25pm UTC](https://gromacs.bioexcel.eu/t/colvar-output-force-and-work/3191 "2021-11-23T17:25:11Z")\
**Posts on this page:** 1\
**Showing post:** 10

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**Author:** ![giacomo.fiorin](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/giacomo.fiorin/32/2862_2.png) [@giacomo.fiorin](https://gromacs.bioexcel.eu/u/giacomo.fiorin)\
**Post date:** [November 30, 2021, 2:41pm UTC](https://gromacs.bioexcel.eu/t/colvar-output-force-and-work/3191/10 "2021-11-30T14:41:42Z")

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For the record, in case if you refer to this issue with index group names:

> [@Error compiling gromacs 2020.5 patched with Colvar module](https://gromacs.bioexcel.eu/t/error-compiling-gromacs-2020-5-patched-with-colvar-module/3048/10):
>
> Dear Prof. Mu error result when make indexFile rest\_index.ndx And group name containing space example : [PROB] , as it. I’m attach imagen from my index file generate with MDAnalysis.

that issue specifically was due to having used spaces inside a group’s name.

The GROMACS index group format (as produced by e.g. `make_ndx`) does not allow for spaces. The main difference between GROMACS and Colvars when a space is there is that GROMACS will just read everything up to the first space to use as the group’s name and discard the rest, whereas Colvars will raise a parsing error.

Giacomo

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