Numerical solution and fast-slow decomposition of a population of weakly coupled systems

The modeling of the microphysics of a population of atmospheric particles interacting through a common medium leads to the solution of a large system of weakly coupled differential-algebraic equations. An implicit time discretization of the system of differential-algebraic equations is solved with a Newton method at each time step. The structure of the global system and the sparsity of the Newton matrix allow the efficient use of a Schur complement approach for the decoupling of the various subsystems at the discrete level. A numerical approach for the decomposition of the population into fast and slow subsystems is proposed. Numerical results are presented for organic atmospheric particles to illustrate the properties of the method.