The method by which circuit equations are formulated is essential to a computer-aided circuit analysis program. It affects significantly the setup time, the programming effort, the storage requirement, and the performance of the program. A linear time-invariant circuit with n nodes and b branches is completely specified by its network topology and branch constraints. The fundamental equations that describe the equilibrium conditions of a circuit are the Kirchhoff’s current law equations, the Kirchhoff ’s voltage law equations, and the equations which characterize the individual circuit elements. Two methods are popular: the sparse tableau approach and the modified nodal approach. The main advantage of the sparse tableau approach is its generality (i.e., all circuit unknowns including branch current/ voltage and node-to-datum voltage can be obtained in one pass). Since the number of equations is usually very large, an efficient sparse linear system solver is essential.