lammps/python/examples/demo.py

#!/usr/bin/env python -i
# preceding line should have path for Python on your machine

# demo.py
# Purpose: illustrate use of many library interface commands
# Syntax:  demo.py
#          uses in.demo as LAMMPS input script

from __future__ import print_function
import sys

# parse command line

argv = sys.argv
if len(argv) != 1:
  print("Syntax: demo.py")
  sys.exit()

from lammps import lammps
lmp = lammps()

# test out various library functions after running in.demo

lmp.file("in.demo")

print("\nPython output:")

natoms = lmp.extract_global("natoms",0)
mass = lmp.extract_atom("mass",2)
x = lmp.extract_atom("x",3)
print("Natoms, mass, x[0][0] coord =",natoms,mass[1],x[0][0])

temp = lmp.extract_compute("thermo_temp",0,0)
print("Temperature from compute =",temp)

eng = lmp.extract_variable("eng",None,0)
print("Energy from equal-style variable =",eng)

vy = lmp.extract_variable("vy","all",1)
print("Velocity component from atom-style variable =",vy[1])

vol = lmp.get_thermo("vol")
print("Volume from get_thermo = ",vol)

natoms = lmp.get_natoms()
print("Natoms from get_natoms =",natoms)

xc = lmp.gather_atoms("x",1,3)
print("Global coords from gather_atoms =",xc[0],xc[1],xc[31])

xc[0] = xc[0] + 1.0
lmp.scatter_atoms("x",1,3,xc)

print("Changed x[0][0] via scatter_atoms =",x[0][0])