Nodal Analysis – Wikipedia introduction to the Nodal Analysis method that we use in GUNNS.
Hydaulic Analogy – Wikipedia article on the Hydraulic-Electric analogy that we make use of in GUNNS.

F. N. Najm (2010). Circuit Simulation. Wiley. ISBN 978-0-470-53871-5. This has been very valuable to us throughout the development of GUNNS, particularly with respect to electrical aspect models. It’s a good reference on nodal analysis, the companion model and the backward-Euler discretization that we use.