A New Active-Passive Network Simulator for Transient Field Problems

The computer system described in this paper represents a hydridization of analog and digital techniques. A wide variety of problems characterized by partial differential equations are simulated by means of a network consisting only of positive and negative resistors. No reactors are used, the negative resistors being realized with the aid of dc amplifiers. Unlike conventional analog methods, the time as well as the space variables are approximated by finite-difference expressions; thus the solution proceeds step-wise in time as on a digital computer. Only implicit difference equations are instrumented, so that there is no danger of computational instability no matter how large the time increment. Among the field problems treated by this computer are problems characterized by the diffusion equation, the wave equation, the biharmonic (beam) equation, and various modified forms of these equations.