please refer to
K. S. Kundert, The designer’s guide to SPICE and Spectre. Boston: Kluwer Academic Publishers, 1995.
4.3.5.3 Initial Conditions Versus Nodesets
Nodesets and initial conditions are implemented in a similar manner but their effect is quite different. Initial conditions actually define the initial solution, whereas nodesets only influence it. Also, while nodesets affect both the DC and transient analyses, initial conditions only affect the transient analysis. The transient waveforms start from initial conditions. Nodesets are usually used only as a convergence aid and do not affect the final results (unless the circuit has more than one solution, such as a latch, in which case nodesets act to bias the simulator towards finding the solution closest to the nodeset values).
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