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2.7 Time-Domain Analysis of Nonlinear Dynamic Circuits 119
equations is then solved for the voltages and currents using the multi-dimensional Newton-Raphson
method.
Circuit equations are usually stiff, which means that their solutions involve both very rapid and very
slow transients. To avoid loss of accuracy and convergence problems during rapid transients as well
as excessive computation time requirements for slow transients the step size is chosen adaptively at
each time step according to the curvature of the waveform. Whenever a waveform changes quickly
the step size is cut back whereas it is increased during periods of latency. The behavior of the
step size control algorithm depends on the values of five parameters which will be discussed in the
following section. The associated NDAESolve options by which the default parameter settings can be
changed are StartingStepSize, MaxStepSize, MinStepSize, StepSizeFactor, and MaxDelta.
Figure 7.3 shows a flow graph of the algorithm implemented in NDAESolve.