To model these types of processes people usually use stochastic processes (https://en.wikipedia.org/wiki/Stochastic_process https://en.wikipedia.org/wiki/Stocha

To model these types of processes people usually use stochastic processes (https://en.wikipedia.org/wiki/Stochastic_process https://en.wikipedia.org/wiki/Stochastic_process). I don't know what the author used, but seems inaccurate.