Euler equations on a quadrilateral grid.  
A chevron shaped grid is used that is not orthogonal.

The Sod Riemann problem is solved in the x-direction on this grid.
See setprob.f and qinit.f.   
fdisc.f is used to specify the initial discontinuity.

Using extrapolation boundary conditions causes some problems at the top and
bottom boundaries since extrapolation is done in the direction of the grid
lines instead of normal to the boundary.  Solid wall boundary conditions at
these boundaries gives much better results.

Set PlotType=4 to plot a scatter plot of the results vs. x and compare
with the true Riemann solution stored in rpsoln.

WARNING: This example was modified February, 2006 to use
Version 4.3 of clawpack and the associated matlab scripts.