# Input signal - change variable function at time t

**URL:** <https://discourse.julialang.org/t/input-signal-change-variable-function-at-time-t/63925>\
**Category:** Tooling\
**Tags:** ode\
**Created:** [July 2, 2021, 8:15am UTC](https://discourse.julialang.org/t/input-signal-change-variable-function-at-time-t/63925 "2021-07-02T08:15:37Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![minhnguyen](https://avatars.discourse-cdn.com/v4/letter/m/35a633/32.png) [@minhnguyen](https://discourse.julialang.org/u/minhnguyen)\
**Post date:** [July 2, 2021, 8:15am UTC](https://discourse.julialang.org/t/input-signal-change-variable-function-at-time-t/63925/1 "2021-07-02T08:15:37Z")

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Hi everyone,

I’m dealing with differential equations with additional variable function i(t) which is a signal input that is on and off and then on. I don’t know how to integrate this into my function

function twosystem(du, u, p, t)  
du[1] = (1 / ta) \* (i(t) - u[1]) - b \* u[2]  
du[2] = (1 / tw) \* (u[1] - u[2])  
end

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**Author:** ![zdenek\_hurak](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/zdenek_hurak/32/53118_2.png) [@zdenek\_hurak](https://discourse.julialang.org/u/zdenek_hurak)\
**Post date:** [July 2, 2021, 9:01am UTC](https://discourse.julialang.org/t/input-signal-change-variable-function-at-time-t/63925/2 "2021-07-02T09:01:58Z")

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Example 3 at [Ordinary Differential Equations · DifferentialEquations.jl](https://diffeq.sciml.ai/stable/tutorials/ode_example/)