# DifferentialEquations: Gaussian error term in one of the equations makes it extremely slow (and error prone)

**URL:** https://discourse.julialang.org/t/differentialequations-gaussian-error-term-in-one-of-the-equations-makes-it-extremely-slow-and-error-prone/105647
**Category:** Modelling & Simulations
**Tags:** question
**Created:** [November 1, 2023, 10:03am UTC](https://discourse.julialang.org/t/differentialequations-gaussian-error-term-in-one-of-the-equations-makes-it-extremely-slow-and-error-prone/105647 "2023-11-01T10:03:25Z")
**Posts on this page:** 1
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### Author: ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [November 1, 2023, 11:56am UTC](https://discourse.julialang.org/t/differentialequations-gaussian-error-term-in-one-of-the-equations-makes-it-extremely-slow-and-error-prone/105647/2 "2023-11-01T11:56:37Z")

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> [@MvanSteenbergen](#):
>
> Thirdly, the rate of the noise ζ(_t_) is chosen at 0.01, meaning that the perceived environment variable _z_ changes every 0.01 days (noise will be generated every 14.4 min). It is a compromise between the duration of variability of the symptoms of psychiatric disorders and their environment (i.e., considering a psychological state change every 14.4 min). In other words, the model provides a smoothness of 14.4 min, i.e., informs about potential changes in its variables approximately every quarter of an hour.

You should implement this as a discrete callback which changes a parameter according this this schedule. I recommend using a PeriodicCallback.

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