# 2D Noh Strong Shock
This test highlights the ability of a code to track a high Mach number shock. Parameters from Liska and Wendroff 2003. The test consists of an infinitely strong circular shock radiating from the origin. There is initially a constant density of 1.0 across the grid and a velocity of 1.0 towards the center everywhere. Pressure is set to $10^{-6}$ everywhere. Gamma is set to 1.66666667. This test is performed with the default hydro build (`cholla/builds/make.type.hydro`) and Van Leer integrator. Full initial conditions can be found in `cholla/src/grid/initial_conditions.cpp`under `Noh_2D()`. 

The parameter file can be found at: {repository-file}`examples/2D/Noh_2D.txt`

## Parameter file:

```
#
# Parameter File for the 2D Noh problem described in Liska, 2003.
#

######################################
# number of grid cells in the x dimension
nx=200
# number of grid cells in the y dimension
ny=200
# number of grid cells in the z dimension
nz=1
# output time
tout=2.0
# how often to output
outstep=0.01
# value of gamma
gamma=1.66666667
# name of initial conditions
init=Noh_2D
# domain properties
xmin=0.0
ymin=0.0
zmin=0.0
xlen=1.0
ylen=1.0
zlen=1.0
# type of boundary conditions
xl_bcnd=2
xu_bcnd=4
yl_bcnd=2
yu_bcnd=4
zl_bcnd=0
zu_bcnd=0
custom_bcnd=noh
# path to output directory
outdir=./
```
Upon completion, you should obtain 201 output files. The evolution of the density is shown below. Examples of how to plot projections and slices can be found in the [General 2D plotting example](../../PythonExamples/2D-plotting.md).

:::{video} noh-docs.mp4
    :width: 700
    :height: 500
    :align: center
    :autoplay:
    :loop:
:::

We can compare to the [Fyris Alpha code](https://www.mso.anu.edu.au/fyris/lw2dnoh.html):  

:::{figure} fyris-alpha.png
:::