# 3D Adaibatic Expansion Test

This test demonstrates simple adiabatic expansion in a cosmological frame.  The initial conditions are the critical density in baryons at the starting redshift, T=100K, and no bulk velocity. Gamma is set to 5/3. This test is performed with the cosmology build (`cholla/builds/make.type.cosmology`) and SIMPLE integrator.
Full initial conditions can be found in `cholla/src/grid/initial_conditions.cpp`under `Adiabatic_Expansion()`. 

## Parameter file:

This parameter file can be found in [examples/3D/Adiabatic_Expansion.txt](https://github.com/cholla-hydro/cholla/blob/main/examples/3D/Adiabatic_Expansion.txt) on the `dev` branch.
```
#
# Parameter File for the 3D Adiabatic Expansion test.
#

######################################
# number of grid cells in the x dimension
nx=256
# number of grid cells in the y dimension
ny=32
# number of grid cells in the z dimension
nz=32
# output time
tout=1000
# how often to output
outstep=1000
# value of gamma
gamma=1.66666667
# name of initial conditions
init=Adiabatic_Expansion
#Cosmological Parameters
Init_redshift=20.0
#Init_redshift=0.998294693667
H0=50.0
Omega_M=1.0
Omega_L=0.0
Omega_b=1.0
temperature_floor=1.0e-2
scale_outputs_file=scale_output_files/outputs_adiabatic_expansion.txt
# domain properties
xmin=0.0
ymin=0.0
zmin=0.0
xlen=64000.0
ylen=8000.0
zlen=8000.0
# type of boundary conditions
xl_bcnd=1
xu_bcnd=1
yl_bcnd=1
yu_bcnd=1
zl_bcnd=1
zu_bcnd=1
# path to output directory
indir=ics/
outdir=./
```
  
Upon completion, you should obtain two output files. The final density, velocity, and temperature in physical units are shown below. Examples of how to plot projections and slices can be found in the [General 2D plotting example](../../PythonExamples/2D-plotting.md). 
:::{figure} adiabatic_expansion.png
Adiabatic Expansion test solution from Cholla.
:::