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

GROMACS version: 2019.2
GROMACS modification: No

Hello, I am trying to do dihedral PCA analysis explained on this GROMACS link: .

It says to make index file of dihedrals of interests by using [gmx 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?


Can anyone help with this? Thanx.