xyst

Add artificial viscosity to ZalCG

Both 2nd-, and 4th-order dissipation. Based on Eqs. (10.49) and (10.53)
in Lohner, An Introduction to Applied CFD Techniques, Wiley, 2008.

Separately configurable, both off by default. Example:

stab2 = true
stab2coef = 0.1

stab4 = true