A new and simple method to simulate a multielement source or astigmatic source in standard optical design software is presented. The technique can be used to define a laser diode, an array of laser diodes, a screen pixel, or other kind of multielement or astigmatic source. This paper shows how the standard classical approach using an astigmatic point source distance model fails when simulating a laser diode. A new approach is proposed that defines the source as an object in a single plane. This allows the use of powerful optimization in the optical design software without restriction. Some examples are presented.