Entropy Fix Examples with Burger's Eqn

Example [book/chap12/efix] to accompany the book Finite Volume Methods for Hyperbolic Problems by R. J. LeVeque.

Converted to Clawpack 5.4.0 form in 2017.

Burgers' equation with a transonic rarefaction wave.

Comparison of results obtained with or without the entropy fix. This is set in the Riemann solver rp1_burgers.f90 by modifying the variable efix.

Note: also try changing mx in to an odd value (e.g. 61 instead of 60). Then there is one grid cell with the value 0.5 at x=0 and a different weak solution is obtained.

Note: The solution also looks much smoother if you set order=2 in instead of order=1.