In a computer simulation of an analog device in a digital circuit, a piece-wise linear lookup table is used to determine the channel resistance of the transistors in the analog device, allowing the node voltages to take on non-digital values. The piece-wise linear lookup table contains a set of channel resistances corresponding respectively to gate-to-source voltages. The program uses multi-terminal binary decision graphs (MTBDDs) to represent non-digital resistances, capacitances and voltages in the circuit as a function of symbolic inputs. The program can analyze circuits containing more than two voltage sources by modeling voltage sources with voltage dividers between the maximum and minimum voltages in the circuit.