git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@14326 f3b2605a-c512-4ea7-a41b-209d697bcdaa

python/examples/split.py

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+#!/usr/bin/env python -i
+# preceeding line should have path for Python on your machine
+
+# split.py
+# Purpose: similar to simple.py, but first the world communicator
+#   is split in two halves and LAMMPS is run only on one partition
+# Syntax:  split.py in.lammps
+#          in.lammps = LAMMPS input script
+
+import sys
+
+# parse command line
+
+argv = sys.argv
+if len(argv) != 2:
+  print "Syntax: simple.py in.lammps"
+  sys.exit()
+
+infile = sys.argv[1]
+
+me = 0
+
+# this example *only* works with mpi4py version 2.0.0 or later
+
+from mpi4py import MPI
+comm = MPI.COMM_WORLD
+me = comm.Get_rank()
+nprocs = comm.Get_size()
+
+# create two subcommunicators
+
+if me < nprocs // 2:  color = 0
+else: color = 1
+  
+split = comm.Split(color,key=0)
+
+if color == 0:
+  from lammps import lammps
+  lmp = lammps(comm=split)
+
+  # run infile one line at a time
+
+  lines = open(infile,'r').readlines()
+  for line in lines: lmp.command(line)
+
+  # run 10 more steps
+  # get coords from LAMMPS
+  # change coords of 1st atom
+  # put coords back into LAMMPS
+  # run a single step with changed coords
+
+  lmp.command("run 10")
+  x = lmp.gather_atoms("x",1,3)
+  epsilon = 0.1
+  x[0] += epsilon
+  lmp.scatter_atoms("x",1,3,x)
+  lmp.command("run 1");
+
+  f = lmp.extract_atom("f",3)
+  print "Force on 1 atom via extract_atom: ",f[0][0]
+
+  fx = lmp.extract_variable("fx","all",1)
+  print "Force on 1 atom via extract_variable:",fx[0]
+  print "Proc %d out of %d procs has" % (me,nprocs), lmp
+  print "Calculation on partition 0 complete"
+
+else:
+  # could run a 2nd calculation on second partition
+  #   with different LAMMPS instance or another code
+  # in this case, just sleep on second partition
+  
+  import time
+  time.sleep(2)
+  print "Calculation on partition 1 complete"
+
+# shutdown mpi4py
+  
+comm.Barrier()
+MPI.Finalize()