# How can I disable the event handler in a fixed time interval after an event?

**URL:** <https://discourse.julialang.org/t/how-can-i-disable-the-event-handler-in-a-fixed-time-interval-after-an-event/110823>\
**Category:** Specific Domains\
**Tags:** differentialequation\
**Created:** [February 27, 2024, 6:08am UTC](https://discourse.julialang.org/t/how-can-i-disable-the-event-handler-in-a-fixed-time-interval-after-an-event/110823 "2024-02-27T06:08:56Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![xiaoming](https://avatars.discourse-cdn.com/v4/letter/x/a6a055/32.png) [@xiaoming](https://discourse.julialang.org/u/xiaoming)\
**Post date:** [February 27, 2024, 6:08am UTC](https://discourse.julialang.org/t/how-can-i-disable-the-event-handler-in-a-fixed-time-interval-after-an-event/110823/1 "2024-02-27T06:08:56Z")

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I have checked the document of DifferentialEquations.jl about the Event handler page. It seems that I should set `repeat_nudge` in a `ContinuousCallback`. However, it doesn’t work.

Here is an MME:

```julia
using OrdinaryDiffEq, StaticArrays

function f(x, p, t)
    SA[x[2], -x[1]]
end

function condition(u, t, integrator)
    u[1] - 1
end

function affect(integ)
    @show integ.t
end

cb = ContinuousCallback(condition, affect, repeat_nudge=0.3)

prob = ODEProblem(f, SA[0.0, 1.001], (0, 2), callback=cb)

sol = solve(prob, Tsit5())

```

I expected that the length of the time interval between two events is greater than 0.3. However, I got

```julia
integ.t = 1.526059239285522
integ.t = 1.6155612263459136

```

---

<div class="post-metadata">

**Author:** ![SteffenPL](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/steffenpl/32/206270_2.png) [@SteffenPL](https://discourse.julialang.org/u/SteffenPL)\
**Post date:** [February 27, 2024, 6:28am UTC](https://discourse.julialang.org/t/how-can-i-disable-the-event-handler-in-a-fixed-time-interval-after-an-event/110823/2 "2024-02-27T06:28:28Z")

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Since `repeat_nudge` only defines the next sign check, it might be that at `1.526 + 0.3`, the first sign check happened, which triggered a root search, finding the next closest zero.

In the concrete case, you could consider using `affect_neg! = (integ) -> nothing` instead, e.g. only do something when the sign change is upcrossing (`affect!`) and do nothing for downcrossing sign change.

---

<div class="post-metadata">

**Author:** ![xiaoming](https://avatars.discourse-cdn.com/v4/letter/x/a6a055/32.png) [@xiaoming](https://discourse.julialang.org/u/xiaoming)\
**Post date:** [February 27, 2024, 9:14am UTC](https://discourse.julialang.org/t/how-can-i-disable-the-event-handler-in-a-fixed-time-interval-after-an-event/110823/3 "2024-02-27T09:14:44Z")

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Thank you for explaining to me how `repeat_nudge` works. What I want to do is:

- after an event, disable the event handler in a fixed time;
- after this fixed time, reinitialize the event handler.

For this concrete example, What I want to do is the following. The event begins with `condition<0`, and hits `0` at `t=1.526` and then the event status becomes `condition>0`. For a fixed time, see `0.3`, the event handler starts work at `1.526+0.3` as its initial status, i.e. even if `condition<0` at `t=1.526+0.3` and condition crosses zero again, the function `affect!` won’t trigger.

---

<div class="post-metadata">

**Author:** ![SteffenPL](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/steffenpl/32/206270_2.png) [@SteffenPL](https://discourse.julialang.org/u/SteffenPL)\
**Post date:** [February 27, 2024, 9:21am UTC](https://discourse.julialang.org/t/how-can-i-disable-the-event-handler-in-a-fixed-time-interval-after-an-event/110823/4 "2024-02-27T09:21:05Z")

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You maybe can use `rootfind = RightRootFind` to avoid any backwards steps.  
(But I didn’t try.)

I think callbacks should not have an internal state. In that case, it would be more idiomatic to integrate the delay time since the last callback into the state variable of the ODE.

For example, you could add a third variable `x[3]` with `du[x] = -1` which measures how much time after the last callback passed.

```julia
using OrdinaryDiffEq

f(du, x, p, t) = du .= (x[2], -x[1], -1.0)

condition(u, t, integrator) = u[3] <= 0.0 ? u[1] - 1 : NaN

function affect(integ)
    @show integ.t
    integ.u[3] = 0.3
end

cb = ContinuousCallback(condition, affect)

prob = ODEProblem(f, [0.0, 1.001, 0.0], (0, 10), callback=cb)

sol = solve(prob, Tsit5())

```

which gives

```julia
integ.t = 1.5260514221058505
integ.t = 7.805140367104949

```

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<div class="post-metadata">

**Author:** ![xiaoming](https://avatars.discourse-cdn.com/v4/letter/x/a6a055/32.png) [@xiaoming](https://discourse.julialang.org/u/xiaoming)\
**Post date:** [February 27, 2024, 9:29am UTC](https://discourse.julialang.org/t/how-can-i-disable-the-event-handler-in-a-fixed-time-interval-after-an-event/110823/5 "2024-02-27T09:29:13Z")

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I haven’t thought of that. It is a working solution!!! I can use an extra parameter, instead of a state, to record the last event time.