Add stabilization parameter to shallow water example

test/hyperbolic/shallowwater.ufl

@@ -27,7 +27,8 @@ bflux = as_matrix([[-q0,                  -q1],
 
 
 # Define numerical fluxes to choose from
-llf_flux = dot(avg(flux), n) - 0.5*jump(u)
+alpha = Max(abs(n[0]*q0('+') + n[1]*q1('+')) + sqrt(g*h('+')), abs(n[0]*q0('-') + n[1]*q1('-')) + sqrt(g*h('-')))
+llf_flux = dot(avg(flux), n) - 0.5*alpha*jump(u)
 boundary_flux = 0.5*dot(flux + bflux, n) + as_vector([0., q0, q1])
 numerical_flux = llf_flux