document and add unit tests for lammps_set_fix_external_callback()

unittest/python/python-fix-external.py

@@ -0,0 +1,42 @@
+import sys,os,unittest
+from ctypes import *
+from lammps import lammps
+
+# add timestep dependent force
+def callback_one(lmp, ntimestep, nlocal, tag, x, f):
+    for i in range(nlocal):
+        f[i][0] = float(ntimestep)
+        f[i][1] = float(ntimestep)
+        f[i][2] = float(ntimestep)
+
+class PythonExternal(unittest.TestCase):
+    def testExternalCallback(self):
+        """Test fix external from Python with pf/callback"""
+
+        machine=None
+        if 'LAMMPS_MACHINE_NAME' in os.environ:
+            machine=os.environ['LAMMPS_MACHINE_NAME']
+        lmp=lammps(name=machine, cmdargs=['-nocite', '-log','none', '-echo', 'screen'])
+
+        # a few commands to set up simple system
+        basic_system="""lattice sc 1.0
+                        region box block -1 1 -1 1 -1 1
+                        create_box 1 box
+                        create_atoms 1 box
+                        mass 1 1.0
+                        pair_style zero 0.1
+                        pair_coeff 1 1
+                        velocity all set 0.1 0.0 -0.1
+                        thermo 5
+                        fix 1 all nve
+                        fix ext all external pf/callback 5 1
+"""
+        lmp.commands_string(basic_system)
+        lmp.set_fix_external_callback("ext",callback_one,lmp)
+        lmp.command("run 10 post no")
+        self.assertAlmostEqual(lmp.get_thermo("temp"),1.0/30.0,14)
+
+##############################
+if __name__ == "__main__":
+    unittest.main()
+