Zero-Crossing Detection for Fixed-Step Solvers

 Zero-crossing detection is now supported in Simulink® with fixed-step solvers. To see where this feature can be beneficial, watch an example with a self-resetting integrator.

A variable-step solver dynamically adjusts the time step size, causing it to increase when a variable is changing slowly and to decrease when the variable changes rapidly. This behavior causes the solver to take many small steps in the vicinity of a discontinuity because the variable is rapidly changing in this region. This improves accuracy but can lead to excessive simulation times.

Simulink® uses a technique known as zero-crossing detection to accurately locate a discontinuity without resorting to excessively small time steps. Usually this technique improves simulation run time, but it can cause some simulations to halt before the intended completion time.

Simulink uses two algorithms for this purpose: nonadaptive and adaptive. For information about these techniques, see Zero-Crossing Algorithms.