Analog and Hybrid Computer Programming, 2nd Edition

F A sine/cosine generator

In some cases, such as the inverted pendulum simulation which was used to train a machine learning system, basic harmonic functions such as sin(φ) and cos(φ) cannot be generated using the quadrature generator described in section 6.33, figure 6.118, because computing element variations will cause φ̇ and the derived functions sin(φ) and cos(φ) to drift apart over time.

If the argument φ can be guaranteed to be in an interval like [−1, 1], functions like sin(φ), etc., can be generated using special function generators based on polygonal approximation. The AD639²²⁸ is a rare but useful integrated circuit which generates basic trigonometric functions; this was used to build the dedicated function generator shown in figure ...