# Gmx angle error

**URL:** <https://gromacs.bioexcel.eu/t/gmx-angle-error/6055>\
**Category:** User discussions\
**Tags:** analysis-tools\
**Created:** [March 27, 2023, 5:31pm UTC](https://gromacs.bioexcel.eu/t/gmx-angle-error/6055 "2023-03-27T17:31:08Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Lois](https://avatars.discourse-cdn.com/v4/letter/l/5f8ce5/32.png) [@Lois](https://gromacs.bioexcel.eu/u/Lois)\
**Post date:** [March 27, 2023, 5:31pm UTC](https://gromacs.bioexcel.eu/t/gmx-angle-error/6055/1 "2023-03-27T17:31:08Z")

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GROMACS version: 2016.4  
GROMACS modification: No

Hi all,

I’m performing simulations with a coarse-grained bead and spring model of a polymer and want to measure the average of each dihedral in the system. I use:

gmx\_mpi angle -f traj\_comp.xtc -n index.ndx -ov -type dihedral

for several systems. One of them brings up the following error:

Fatal error:  
angle (-nan) index out of range (0…360) : -214748364

but I’m unsure about what’s happened because I checked my index file and there are no issues and I’ve used the same method for every other system and there’s been no problem. Also every time I try the analysis, the error comes up at different times along the trajectory. Sometimes it happens straight away and others after going through 2 microseconds of the trajectory. Has anyone come across this before and know what it means?

Thanks.