"E pluribus unum" or How to Derive Single-equation Descriptions for   Output-quantities in Nonlinear Circuits using Differential Algebra
  In this paper we describe by a number of examples how to deduce one single characterizing higher order differential equation for output quantities of an analog circuit.   In the linear case, we apply basic "symbolic" methods from linear algebra to the system of differential equations which is used to model the analog circuit. For nonlinear circuits and their corresponding nonlinear differential equations, we show how to employ computer algebra tools implemented in Maple, which are based on differential algebra. 
Eberhard H.-A. Gerbracht