# Gmx angle Fatal error: Can not combine angles with trr dump

**URL:** <https://gromacs.bioexcel.eu/t/gmx-angle-fatal-error-can-not-combine-angles-with-trr-dump/6587>\
**Category:** User discussions\
**Created:** [June 9, 2023, 4:43pm UTC](https://gromacs.bioexcel.eu/t/gmx-angle-fatal-error-can-not-combine-angles-with-trr-dump/6587 "2023-06-09T16:43:01Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![srdjan](https://avatars.discourse-cdn.com/v4/letter/s/e495f1/32.png) [@srdjan](https://gromacs.bioexcel.eu/u/srdjan)\
**Post date:** [June 9, 2023, 4:43pm UTC](https://gromacs.bioexcel.eu/t/gmx-angle-fatal-error-can-not-combine-angles-with-trr-dump/6587/1 "2023-06-09T16:43:01Z")

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GROMACS version: 2019.2  
GROMACS modification: No

Hello, I am trying to do dihedral PCA analysis explained on this GROMACS link: [https://manual.gromacs.org/2021/reference-manual/analysis/dihedral-pca.html](https://manual.gromacs.org/2021/reference-manual/analysis/dihedral-pca.html) .

It says to make index file of dihedrals of interests by using [gmx mk\_angndx]([https://manual.gromacs.orggmx-mk-angndx](https://manual.gromacs.orggmx-mk-angndx) and than use gmx angela with flat -or to create trr “trajectory” containing sin and cos of dihedral angles.

But when I try to do this command, I get that I cannot combine angles with trr dump, but I don’t understand why.  
Even on link for gmx angle is written that -or will write trr file.

The command I used was: gmx angle -f Backbone.xtc -n dihedrals.ndx -or .

Can someone help me with this?

Thanx.

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<div class="post-metadata">

**Author:** ![srdjan](https://avatars.discourse-cdn.com/v4/letter/s/e495f1/32.png) [@srdjan](https://gromacs.bioexcel.eu/u/srdjan)\
**Post date:** [September 11, 2023, 11:59am UTC](https://gromacs.bioexcel.eu/t/gmx-angle-fatal-error-can-not-combine-angles-with-trr-dump/6587/2 "2023-09-11T11:59:02Z")

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Can anyone help with this? Thanx.