# Solving and ODE depending on external disturbances

**URL:** <https://discourse.julialang.org/t/solving-and-ode-depending-on-external-disturbances/101162>\
**Category:** General Usage\
**Created:** [July 4, 2023, 9:51am UTC](https://discourse.julialang.org/t/solving-and-ode-depending-on-external-disturbances/101162 "2023-07-04T09:51:33Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Maria\_Adelaide\_Loffa](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/maria_adelaide_loffa/32/51045_2.png) [@Maria\_Adelaide\_Loffa](https://discourse.julialang.org/u/Maria_Adelaide_Loffa)\
**Post date:** [July 4, 2023, 9:51am UTC](https://discourse.julialang.org/t/solving-and-ode-depending-on-external-disturbances/101162/1 "2023-07-04T09:51:33Z")

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Hi everyone, I am new to Julia and I was trying to solve and ODE which depends on an exeternal disturbance vector. For every timestep, it needs to evaluate a different values from that vector.  
Initially, I tried with a sin/cos function and the ODE worked, but I tried with a simple vector, but the solution doesn’t seem to consider a changing value.  
Does someone know how to help me?

Hers it’s my code:  
using DifferentialEquations, Plots, Flux, DiffEqFlux, DiffEqCallbacks

function RC!(du,u,p,t)  
Rv, Ci = p  
Text = ext\_disturbance(t)  
phih= ext\_disturbance2(t)

```
du[1] = 1/(Rv*Ci) .* (Text .- u[1]) .+ phih/Ci

```

end

u0= [5.0]  
tspan= (0.0, 30.0)  
t= range(0.0, 30.0, length=10)  
p= [0.05, 10.0]

#Testerna=range(-2,10, length=100)  
#phih= range(0,100, length=100);  
Testerna = [1,2,3,4,5,6,7,8,9,10]  
phih = [10, 20, 30, 40, 50, 60 ,70 ,80 ,90 ,100]  
function ext\_disturbance(t)  
for (k,t) in enumerate(Testerna)  
disturbance = Testerna[k]  
return Testerna[k]  
end  
end

function ext\_disturbance2(t)  
for (m,t) in enumerate(phih)  
disturbance2 = phih[m]  
return phih[m]  
end  
end

prob= ODEProblem(RC!, u0, tspan, p)  
sol= solve(prob, Tsit5(), saveat=t)[1,:]  
plot(sol, label = “reale”)

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<div class="post-metadata">

**Author:** ![baggepinnen](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/baggepinnen/32/693_2.png) [@baggepinnen](https://discourse.julialang.org/u/baggepinnen)\
**Post date:** [July 4, 2023, 1:31pm UTC](https://discourse.julialang.org/t/solving-and-ode-depending-on-external-disturbances/101162/2 "2023-07-04T13:31:10Z")

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> [@Maria\_Adelaide\_Loffa](#):
>
> function ext\_disturbance(t)  
> for (k,t) in enumerate(Testerna)  
> disturbance = Testerna[k]  
> return Testerna[k]  
> end  
> end

you are always returning the first entry of the array `Testerna`. Maybe you would like to use an interpolation to interpolate the disturbance vector? If so, try DataInterpolations.jl:

```julia
disturbance = LinearInterpolation(Testerna, t)

```

and then call the interpolation like this in the dynamics function

```julia
disturbance(t)

```

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<div class="post-metadata">

**Author:** ![Maria\_Adelaide\_Loffa](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/maria_adelaide_loffa/32/51045_2.png) [@Maria\_Adelaide\_Loffa](https://discourse.julialang.org/u/Maria_Adelaide_Loffa)\
**Post date:** [July 5, 2023, 7:38am UTC](https://discourse.julialang.org/t/solving-and-ode-depending-on-external-disturbances/101162/3 "2023-07-05T07:38:04Z")

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Thank you very much!!