On line reduction methods for computer analysis of high-order electrical circuits with widely separated time constants

A greal deal of effort has recently been spent to develop numerical integration techniques suitable for the solution of stiff state equations. Instead of dealing with the integration method itself, a procedure for gradually removing the stiffness of the state equations during the course of the solution is presented. This is accomplished by gradually discarding the state variables corresponding to the eigenvalues having the largest negative real part as their contribution becomes negligible. Since the reduction process is applied to the equations themselves, it can therefore be used to reinforce any numerical method of solution, particularly in those applications where adaptation of an implicit integration method is difficult.