Steps the model, i.e. runs through the step functions of all the agents and increments the timer by one. The function takes no arguments.
This function is called automatically while the model is running, and should not generally be called in user code.
WARNING: This is an internal function. Its use in user code is not recommended or supported, and its signature can change in future updates without warning. Use one of the suggested functions above instead, if applicable.
Return Value — int
The model time.