add test script for compute momentum

# Test compute momentum with by comparing it's output with compute reduce

# Script will output the two computations of the total momentum as

# thermo vars - they should be identical

# 3D LJ Poiseuille flow simulation

dimension	3

boundary	p p p

atom_style	atomic

neighbor	0.3 bin

neigh_modify	delay 5

# create geometry

lattice		hcp 0.5

region		box block 0 20 0 10 0 10

create_box	3 box

create_atoms	1 box

mass		1 1.0

mass		2 1.0

mass		3 1.0

# LJ potentials

pair_style	lj/cut 1.0

pair_coeff	* * 1.0 1.0 1.0

# define groups

region	     1 block INF INF INF 1.0 INF INF

group	     lower region 1

region	     2 block INF INF 9.0 INF INF INF

group	     upper region 2

group	     boundary union lower upper

group	     liquid subtract all boundary

set	     group lower type 2

set	     group upper type 3

# temperature settings

compute      mobile liquid temp

velocity     liquid create 1.0 100 temp mobile

fix          1 all nve

fix          2 liquid temp/rescale 200 1.0 2.0 0.02 1.0

fix_modify   2 temp mobile

velocity     boundary set 0.0 0.0 0.0

fix	     4 lower setforce 0.0 0.0 0.0

fix	     5 upper setforce 0.0 0.0 0.0

fix	     6 liquid addforce 0.1 0.0 0.0

# Compute total momentum

compute mom liquid momentum

# Comparison (momentum variables + compute reduce)

variable mx atom mass*vx

variable my atom mass*vy

variable mz atom mass*vz

compute mom_red liquid reduce sum v_mx v_my v_mz

# Run

timestep	0.003

thermo		1000

thermo_style custom step c_mom_red[*] c_mom[*]

run		100000