Multiple Equations
ParX can also deal with a model with multiple equations.
Here we have the most basic model for a Bipolar Transistor.
It contains four variables: two voltages across the junctions
vbe and vbc,
and two terminal currents ib and ic.
Given the two voltages, we should be able to calculate the corresponding currents.
This requires two equations or two residuals.
Here the assert function is called with the condition
qb > 0 is not satisfied.
This signals the optimizer that the model could not be evaluated for the given input.