# 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