GAUSS-SEIDEL ITERATION FOR STIFF ODES FROM CHEMICAL-KINETICS

A simple Gauss-Seidel technique is proposed that exploits the special form of the chemical kinetics equations. Classical Aitken extrapolatio n is applied to accelerate convergence. The technique is meant for imp lementation in stiff solvers that are used in long range transport air pollution codes using operator splitting. Splitting necessarily gives rise to a great deal of integration restarts. Because the Gauss-Seide l iteration works matrix free, it has much less overhead than the modi fied Newton method. Start-up costs therefore can be kept low with this technique. Preliminary promising numerical results are presented for a prototype of a second order backward differentiation formula (BDF) s olver applied to a stiff ordinary differential equation (ODE) from atm ospheric chemistry. A favourable comparison with the general purpose B DF code DASSL is included. The matrix free technique may also be of in terest for other chemically reacting fluid flow problems.