This research is applying the principal investigator's previous work in the area of nonlinear circuit theory to make major enhancements to the way designers simulate analog circuits. In particular, improvements to the continuation methods of solving dc operating points of circuits are being made guaranteeing that all of a circuit's operating points will be found during a single analysis. Moreover, continuation methods are being applied to sensitivity analysis of circuits; for example, by making observations of a continuation curve, a designer could determine whether a circuit is prone to a latch up condition. Erroneous models are thought to be a major source of convergence problems and erroneous results in circuit simulation. Another enhancement to circuit simulation includes checking the accuracy of transistor models by verifying that all models satisfy passivity and the no- gain condition.