Renamed fix active to fix propel/self

doc/src/fix_propel_self.txt

@@ -0,0 +1,50 @@
+"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
+
+:link(lws,http://lammps.sandia.gov)
+:link(ld,Manual.html)
+:link(lc,Section_commands.html#comm)
+
+:line
+
+fix active command  :pre
+
+[Syntax:]
+
+fix ID group-ID magnitude
+
+ID, group-ID are documented in "fix"_fix.html command :ulb,l
+addforce = style name of this fix command :l
+magnitude = magnitude of the active force :l
+:ule
+
+[Examples:]
+
+fix active_group all active 1.0
+fix constant_velocity all viscous 1.0
+
+[Description:]
+
+Adds a force of a constant magnitude to each atom in the group. The direction
+of the force is along the axis obtained by rotating the z-axis along the atom's
+quaternion. In other words, the force is along the z-axis in the atom's body
+frame.
+
+:line
+
+[Restart, fix_modify, output, run start/stop, minimize info:]
+
+No information about this fix is written to "binary restart
+files"_restart.html.
+
+This fix is not imposed  during minimization.
+
+[Restrictions:]
+
+This fix makes use of per-atom quaternions to take into
+account the fact that the orientation can rotate and hence the direction
+of the active force can change. Therefore, this fix only works with
+ellipsoidal particles.
+
+[Related commands:]
+
+"fix setforce"_fix_setforce.html, "fix addforce"_fix_addforce.html