The Euler_2D program simulates a shock at Mach 2.95 impacting
a bubble of lower density than the surrounding air.

Boundary conditions
-------------------

The top and bottom boundaries are periodic.
The left and right boundaries are not updated; the initial data is left
in place and not modified. The default simulation never touches these
boundaries.

Plotting
--------

In order to plot the output, use gnuplot:

plot "./shock_bubble.out" using 1:2:3 with image

Parallelisation
---------------

OpenMP
------

Consider which loops can be divided up across multiple processors,
and which data-structures should be processed simultaneously.

MPI
---

You will need to work out an approach to splitting the data up between
processes. I suggest you split the data into strips parallel to the x-axis.