In this paper a digital computer simulation of a class of lumped and/or distributed four-ports is given. The program is used in predicting the behavior of certain types of lumped and/or distributed directional couplers. The simulation is done in the frequency domain. For this purpose a digital computer program called COPLER is presented. The program obtains a matrix characterizing the four-port at a discrete set of requencies given the values of the discrete components or the values per unit length and lengths of the distributed components plus a code vector showing how they are connected. It also may perform a statistical tolerance analysis using a Monte Carlo method. Taking advantage of such a study it can also optimize the network through a random walk.