Calculate the angle between three points

angle [<dataset name>] <mask1> <mask2> <mask3> [out <filename>] [mass]

[<dataset name>] Output data set name.
<maskX> Three atom masks selecting atom(s) to calculate angle for.
[out <filename>] Output file name.
[mass] Use center of mass of atoms in <maskX> instead of geometric center.

Calculate angle (in degrees) between atoms in <mask1>, <mask2>, and <mask3>.

For example, to calculate the angle between the first three atoms in the system and output as an XMGrace file:

angle A123 @1 @2 @3 out A123.agr