. The property that a pair of oriented matroidsM ? L , MR on E have free union and no common (non-zero) covector generalizes oriented matroid duality. This property characterizes when certain systems of equations whose only nonlinearities occur as real monotone bijections have a unique solution for all values of additive parameters. Instances include sign non-singularity of square matrices and generalizations of positive definiteness given by Fiedler and Pt'ak. Other instances of this property include various kinds of characterizations of when an electric network problem is well-posed. Such characterizations have been given in terms of matrix pairs by Sandberg and Willson and in terms of electrical network graphs by Duffin, Minty, Hasler and Neirnyck, and by Nishi and Chua. Cases of the general common covector problem are classified. Natural matroid rank conditions are sufficient for a common covector to exist. An algorithm to construct a common covector by composing certain fundamen...

In recent years, the technique of simpl$cation during gen-eration has turned out to be very promising for the eficient computation of approximate symbolic network functions for large transistor circuits. In this paper it is shown how sym-bolic network functions can be simpl$ed during their genera-tion with any well-known symbolic network analysis method. The underlying algorithm for the different techniques is al-ways a matroid intersection algorithm. It is shown that the most eflcient technique is the two-graph method. An imple-mentation of the simpltjication during generation technique with the two-graph method illustrates its benefits for the sym-bolic analysis of large analog circuits. 1

This paper reviews the main last generation symbolic analyzers, comparing them in terms of functionality, pointing out also their shortcomings. The state-of-the-art in this field is also studied, pointing out directions for future research. 1. INTRODUCTION Circuit analysis is a basic milestone for efficient design of integrated circuits. Ever since powerful computers have been available, designers have developed programs to analyze circuits automatically. Today, all electrical engineering professionals and students use electrical simulators (such as HSPICE or ELDO). However, electrical simulators do not cover all the analysis tasks required for integrated circuit design. Essentially, they only serve to verify the performance of previously sized circuits. Among other things, designers must be able to predict the behavior of unsized circuits by tracing relationships among performance figures and design parameters. These relationships may be in the form of transfer functions, poles and ...