http://xyst.i2p/inciter_laxcg.html
One way to remedy this stiffness and associated convergence problems is to apply a preconditioner to the governing equations. The idea is to write the system as which is solved for the Q vector of primitive variables of pressure, velocity, and temperature, T , The preconditioner is given by where the total enthalpy, H , is related to the total energy as and where the reference velocity is specified as...