g_sgangle(1) computes the angle and distance between two groups

## SYNOPSIS

g_sgangle -f traj.xtc -n index.ndx -s topol.tpr -oa sg_angle.xvg -od sg_dist.xvg -od1 sg_dist1.xvg -od2 sg_dist2.xvg -[no]h -[no]version -nice int -b time -e time -dt time -[no]w -xvg enum -[no]one -[no]z

## DESCRIPTION

Compute the angle and distance between two groups. The groups are defined by a number of atoms given in an index file and may be two or three atoms in size. If -one is set, only one group should be specified in the index file and the angle between this group at time 0 and t will be computed. The angles calculated depend on the order in which the atoms are given. Giving, for instance, 5 6 will rotate the vector 5-6 with 180 degrees compared to giving 6 5.

If three atoms are given, the normal on the plane spanned by those three atoms will be calculated, using the formula P1P2 x P1P3. The cos of the angle is calculated, using the inproduct of the two normalized vectors.

Here is what some of the file options do:

-oa: Angle between the two groups specified in the index file. If a group contains three atoms the normal to the plane defined by those three atoms will be used. If a group contains two atoms, the vector defined by those two atoms will be used.

-od: Distance between two groups. Distance is taken from the center of one group to the center of the other group.

-od1: If one plane and one vector is given, the distances for each of the atoms from the center of the plane is given separately.

-od2: For two planes this option has no meaning.

## FILES

-f traj.xtc Input
Trajectory: xtc trr trj gro g96 pdb cpt

-n index.ndx Input
Index file

-s topol.tpr Input
Run input file: tpr tpb tpa

-oa sg_angle.xvg Output
xvgr/xmgr file

-od sg_dist.xvg Output, Opt.
xvgr/xmgr file

-od1 sg_dist1.xvg Output, Opt.
xvgr/xmgr file

-od2 sg_dist2.xvg Output, Opt.
xvgr/xmgr file

## OTHER OPTIONS

-[no]hno
Print help info and quit

-[no]versionno
Print version info and quit

-nice int 19
Set the nicelevel

-b time 0
First frame (ps) to read from trajectory

-e time 0
Last frame (ps) to read from trajectory

-dt time 0
Only use frame when t MOD dt = first time (ps)

-[no]wno
View output  .xvg .xpm .eps and  .pdb files

-xvg enum xmgrace
xvg plot formatting:  xmgrace xmgr or  none

-[no]oneno
Only one group compute angle between vector at time zero and time t

-[no]zno
Use the  z-axis as reference