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GMX-ANGLE(1)			     GROMACS			    GMX-ANGLE(1)

NAME
     gmx-angle	-  Calculate distributions and correlations for angles and dihe-
     drals

SYNOPSIS
	gmx angle [-f [<.xtc/.trr/...>]] [-n [<.ndx>]] [-od [<.xvg>]]
		  [-ov [<.xvg>]] [-of [<.xvg>]] [-ot [<.xvg>]] [-oh [<.xvg>]]
		  [-oc [<.xvg>]] [-or [<.trr>]] [-b <time>] [-e <time>]
		  [-dt <time>] [-[no]w] [-xvg <enum>] [-type <enum>]
		  [-[no]all] [-binwidth <real>] [-[no]periodic]
		  [-[no]chandler] [-[no]avercorr] [-acflen <int>]
		  [-[no]normalize] [-P <enum>] [-fitfn <enum>]
		  [-beginfit <real>] [-endfit <real>]

DESCRIPTION
     gmx angle computes the angle distribution for a number of angles  or  dihe-
     drals.

     With  option  -ov, you can plot the average angle of a group of angles as a
     function of time. With the -all option, the first graph is the average  and
     the rest are the individual angles.

     With  the -of option, gmx angle also calculates the fraction of trans dihe-
     drals (only for ryckaert-bellemans dihedrals) as function of time, but this
     is probably only fun for a select few. An output file is only generated  if
     -type ryckaert-bellemans is specified.

     With option -oc, a dihedral correlation function is calculated.

     It  should  be noted that the index file must contain atom triplets for an-
     gles or atom quadruplets for dihedrals.  If this is not the case, the  pro-
     gram will crash.

     With  option -or, a trajectory file is dumped containing cos and sin of se-
     lected dihedral angles, which subsequently can be used as input for a prin-
     cipal components analysis using gmx covar.

     Option -ot plots when transitions occur between dihedral rotamers of multi-
     plicity 3 and -oh records a histogram of the  times  between  such  transi-
     tions,  assuming  the  input  trajectory frames are equally spaced in time.
     Output files are only generated if -type dihedral is specified.

OPTIONS
     Options to specify input files:

     -f [<.xtc/.trr/...>] (traj.xtc)
	    Trajectory: xtc trr cpt gro g96 pdb tng h5md

     -n [<.ndx>] (angle.ndx)
	    Index file

     Options to specify output files:

     -od [<.xvg>] (angdist.xvg)
	    xvgr/xmgr file

     -ov [<.xvg>] (angaver.xvg) (Optional)
	    xvgr/xmgr file

     -of [<.xvg>] (dihfrac.xvg) (Optional)
	    xvgr/xmgr file

     -ot [<.xvg>] (dihtrans.xvg) (Optional)
	    xvgr/xmgr file

     -oh [<.xvg>] (trhisto.xvg) (Optional)
	    xvgr/xmgr file

     -oc [<.xvg>] (dihcorr.xvg) (Optional)
	    xvgr/xmgr file

     -or [<.trr>] (traj.trr) (Optional)
	    Trajectory in portable xdr format

     Other options:

     -b <time> (0)
	    Time of first frame to read from trajectory (default unit ps)

     -e <time> (0)
	    Time of last frame to read from trajectory (default unit ps)

     -dt <time> (0)
	    Only use frame when t MOD dt = first time (default unit ps)

     -[no]w (no)
	    View output .xvg, .xpm, .eps and .pdb files

     -xvg <enum> (xmgrace)
	    xvg plot formatting: xmgrace, xmgr, none

     -type <enum> (angle)
	    Type of angle to analyse: angle, dihedral, improper, ryckaert-belle-
	    mans

     -[no]all (no)
	    Plot all angles separately in the averages file, in the order of ap-
	    pearance in the index file.

     -binwidth <real> (1)
	    binwidth (degrees) for calculating the distribution

     -[no]periodic (yes)
	    Print dihedral angles modulo 360 degrees

     -[no]chandler (no)
	    Use Chandler correlation function (N[trans]  =  1,	N[gauche]  =  0)
	    rather  than  cosine correlation function. Trans is defined as phi <
	    -60 or phi > 60.

     -[no]avercorr (no)
	    Average the correlation functions for  the	individual  angles/dihe-
	    drals

     -acflen <int> (-1)
	    Length of the ACF, default is half the number of frames

     -[no]normalize (yes)
	    Normalize ACF

     -P <enum> (0)
	    Order of Legendre polynomial for ACF (0 indicates none): 0, 1, 2, 3

     -fitfn <enum> (none)
	    Fit function: none, exp, aexp, exp_exp, exp5, exp7, exp9

     -beginfit <real> (0)
	    Time where to begin the exponential fit of the correlation function

     -endfit <real> (-1)
	    Time  where  to end the exponential fit of the correlation function,
	    -1 is until the end

KNOWN ISSUES
     * Counting transitions only works for dihedrals with multiplicity 3

SEE ALSO
     gmx(1)

     More information about GROMACS is available at <http://www.gromacs.org/>.

COPYRIGHT
     2026, GROMACS development team

2026.3				  Jun 25, 2026			    GMX-ANGLE(1)
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