add documentation for fix move/python

doc/src/Section_commands.txt

@@ -585,6 +585,7 @@ USER-INTEL, k = KOKKOS, o = USER-OMP, t = OPT.
 "lineforce"_fix_lineforce.html,
 "momentum (k)"_fix_momentum.html,
 "move"_fix_move.html,
+"move/python"_fix_move_python.html,
 "mscg"_fix_mscg.html,
 "msst"_fix_msst.html,
 "neb"_fix_neb.html,

doc/src/fix_python_move.txt

@@ -0,0 +1,102 @@
+"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 move/python command :h3
+
+[Syntax:]
+
+fix move/python pymodule.CLASS :pre
+
+pymodule.CLASS = use class [CLASS] in module/file [pymodule] to compute how to move atoms
+
+[Examples:]
+
+fix  1 all move/python py_nve.NVE
+fix  1 all move/python py_nve.NVE_OPT :pre
+
+[Description:]
+
+The {move/python} fix style provides a way to define ways how particles
+are moved during an MD run from python script code, that is loaded from
+a file into LAMMPS and executed at the various steps where other fixes
+can be executed. This python script must contain specific python class
+definitions.
+
+This allows to implement complex position updates and also modified
+time integration methods. Due to python being an interpreted language,
+however, the performance of this fix can be moderately to significantly
+slower than the corresponding C++ code. For specific cases, this
+performance penalty can be limited through effective use of NumPy.
+
+:line
+
+The python module file has to start with the following code:
+
+from __future__ import print_function
+import lammps
+import ctypes
+import traceback
+import numpy as np
+#
+class LAMMPSFix(object):
+    def __init__(self, ptr, group_name="all"):
+        self.lmp = lammps.lammps(ptr=ptr)
+        self.group_name = group_name
+#
+class LAMMPSFixMove(LAMMPSFix):
+    def __init__(self, ptr, group_name="all"):
+        super(LAMMPSFixMove, self).__init__(ptr, group_name)
+#
+    def init(self):
+        pass
+#
+    def initial_integrate(self, vflag):
+        pass
+#
+    def final_integrate(self):
+        pass
+#
+    def initial_integrate_respa(self, vflag, ilevel, iloop):
+        pass
+#
+    def final_integrate_respa(self, ilevel, iloop):
+        pass
+#
+    def reset_dt(self):
+        pass :pre
+
+Any classes implementing new atom motion functionality have to be
+derived from the [LAMMPSFixMove] class, overriding the available
+methods as needed.
+
+Examples for how to do this are in the {examples/python} folder.
+
+:line
+
+[Restart, fix_modify, output, run start/stop, minimize info:]
+
+No information about this fix is written to "binary restart
+files"_restart.html.  None of the "fix_modify"_fix_modify.html options
+are relevant to this fix.  No global or per-atom quantities are stored
+by this fix for access by various "output
+commands"_Section_howto.html#howto_15.  No parameter of this fix can
+be used with the {start/stop} keywords of the "run"_run.html command.
+This fix is not invoked during "energy minimization"_minimize.html.
+
+[Restrictions:]
+
+This pair style is part of the PYTHON package.  It is only enabled if
+LAMMPS was built with that package.  See the "Making
+LAMMPS"_Section_start.html#start_3 section for more info.
+
+[Related commands:]
+
+"fix nve"_fix_nve.html, "fix python"_fix_python.html
+
+[Default:] none
+

doc/src/fixes.txt

@@ -71,6 +71,7 @@ Fixes :h1
    fix_meso_stationary
    fix_momentum
    fix_move
+   fix_move_python
    fix_mscg
    fix_msst
    fix_mvv_dpd

doc/src/lammps.book

@@ -200,6 +200,7 @@ fix_meso.html
 fix_meso_stationary.html
 fix_momentum.html
 fix_move.html
+fix_move_python.html
 fix_mscg.html
 fix_msst.html
 fix_mvv_dpd.html

src/.gitignore

@@ -908,10 +908,10 @@
 /python_impl.cpp
 /python_impl.h
 /python_compat.h
+/fix_move_python.cpp
+/fix_move_python.h
 /fix_python.cpp
 /fix_python.h
-/fix_python_move.cpp
-/fix_python_move.h
 /pair_python.cpp
 /pair_python.h
 /reader_molfile.cpp