I’m quite new to Julia but i’ve been getting this error for a while. I created a toy scenario similar to this where I define a variable just before using it in a function and it works there. However, I get an UndefVarError while doing the same here.

I’m working on the following function in ChaosTools.jl.

```
function rescale!(integ::MinimalDiscreteIntegrator{true, Vector{S}}, a) where {S<:Vector}
@. du = integ.u[1] + (integ.u[2] - integ.u[1])/a
set_state!(integ,du,2)
# @. integ.u[2] = integ.u[1] + (integ.u[2] - integ.u[1])/a
# u_modified!(integ, true)
end
```

```
Got exception outside of a @test
UndefVarError: du not defined
Stacktrace:
[1] rescale!(integ::DynamicalSystemsBase.MinimalDiscreteIntegrator{true, Vector{Vector{Float64}}, 3, DynamicalSystemsBase.var"#27#28"{DynamicalSystemsBase.DiscreteDynamicalSystem{true, Vector{Float64}, 3, var"#g#8", Nothing, DynamicalSystemsBase.var"#6#12"{ForwardDiff.JacobianConfig{ForwardDiff.Tag{DynamicalSystemsBase.var"#5#11"{var"#g#8", Nothing, Int64}, Float64}, Float64, 3, Tuple{Vector{ForwardDiff.Dual{ForwardDiff.Tag{DynamicalSystemsBase.var"#5#11"{var"#g#8", Nothing, Int64}, Float64}, Float64, 3}}, Vector{ForwardDiff.Dual{ForwardDiff.Tag{DynamicalSystemsBase.var"#5#11"{var"#g#8", Nothing, Int64}, Float64}, Float64, 3}}}}, DynamicalSystemsBase.var"#5#11"{var"#g#8", Nothing, Int64}, Vector{Float64}}, Matrix{Float64}, true}, Int64}, Nothing}, a::Float64)
@ ChaosTools e:\Master Thesis\ChaosTools\ChaosTools.jl\src\chaosdetection\lyapunovs.jl:339
```

I can run the function by simply doing this

```
set_state!(integ,integ.u[1] + (integ.u[2] - integ.u[1])./a,2)
```

however that makes for messy code and I think that way should be working.

Thank you.