@yfclark
Jasak PhD thesis, P112:
In order to improve the solver convergence, it is desirable to increase the diagonal
dominance of the system. Discretisation of the linear part of the source term, Eqn.
(3.36), is closely related to this issue. If Sp < 0, its contribution increases diagonal
dominance and Sp is included into the diagonal. In the case of Sp > 0, diagonal
dominance would be decreased. It is more effective to include this term into the
source and update it when the new solution is available. This measure is, however,
not sufficient to guarantee the diagonal dominance of the matrix.