# ERROR: UndefVarError: \`connect\` not defined in \`Main\`

**URL:** <https://discourse.julialang.org/t/error-undefvarerror-connect-not-defined-in-main/123244>\
**Category:** Modelling & Simulations\
**Tags:** mtk-connect\
**Created:** [November 29, 2024, 11:24am UTC](https://discourse.julialang.org/t/error-undefvarerror-connect-not-defined-in-main/123244 "2024-11-29T11:24:05Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Stephen](https://avatars.discourse-cdn.com/v4/letter/s/96bed5/32.png) [@Stephen](https://discourse.julialang.org/u/Stephen)\
**Post date:** [November 29, 2024, 11:24am UTC](https://discourse.julialang.org/t/error-undefvarerror-connect-not-defined-in-main/123244/1 "2024-11-29T11:24:05Z")

</div>

Hi, I’m reproducing the [Acausal Modeling for Nonlinear Control and Analysis](https://www.youtube.com/watch?v=l3odTEy69UU&t=948s)

```julia
# ===========================================================
# Example from https://www.youtube.com/watch?v=l3odTEy69UU&t=2488s
# ===========================================================
using JuliaSimControl
using ModelingToolkit, OrdinaryDiffEq, ModelingToolkitStandardLibrary
using ModelingToolkitStandardLibrary.Blocks
using ModelingToolkit:D_nounits as D, t_nounits as t 

rc = 0.25 # reference concentration

@mtkmodel MixingTank begin
    @parameters begin
        c0 = 0.8 # Nominal concentration
        T0 = 308.5 # Nominal temperature 
        a1 = 0.2674
        a21 = 1.815
        a22 = 0.4682
        b = 1.5476
        k0 = 1.05e14
        ϵ = 34.2894
    end

    @variables begin
        γ(t), [description = "Reaction speed"]
        xc(t) = c0, [description = "Concentration"]
        xT(t) = T0, [description = "Temperature"]
        xT_c(t) = T0, [description = "Cooling temperature"]
    end

    @components begin
        T_c = RealInput()
        c = RealOutput()
        T = RealOutput()
    end

    begin
        τ0 = 60
        wk0 = k0 / c0
        wϵ = ϵ * τ0
        wa11 = a1 / τ0
        wa12 = c0 / τ0
        wa13 = c0 * a1 / τ0
        wa21 = a21 / τ0
        wa22 = a22 / τ0
        wa23 = T0 * (a21 - b) / τ0
        wb = b / τ0
    end
    
    @equations begin
        γ ~ xc * wk0 * exp(-wϵ / xT)
        D(xc) ~ -wa11 * xc - wa12 * γ + wa13
        D(xT) ~ -wa21 * xT + wa22 * γ + wa23 + wb * xT_c
    
        xc ~ c.u
        xT ~ T.u
        xT_c ~ T_c.u
    end
    
end

tspan = (0.0, 1000.0)

@mtkmodel TankWithInput begin
    @components begin
        input = Constant(k = 306.25) # Constant cooling temperature input
        tank = MixingTank()
    end
    @equations begin
        connect(input.output, :u, tank.T_c)
    end
end

let
    @named model = TankWithInput()  
    cmodel = complete(model)

    ssys = structural_simplify(model)
    prob = ODEProblem(ssys, [], tspan)
    sol = solve(prob, Rodas5P())
    f1 = plot(sol, layout = 2, title = "Open-loop")

    linmod = linearize_named_ss(model, :u, [cmodel.tank.xc, cmodel.tank.xT])
    w = exp10.(-4 : 0.01 : 2)

    plot(f1,
        nyquistplot(linmod, w, legend = :outerright, unit_circle = true, ylims = (-5, 1),
        xlims = (-3, 1), ratio = 1, title = "", ylabel = ""),
        pzmap(linmod, ratio = 1),
        bodeplot(linmod[2, 1], w),
        margin = 1Plots.mm,
        size = (800, 800),
    )
end

```

but this `@named model = TankWithInput()`  
throws an error as  
`ERROR: UndefVarError: 'connect' not defined in 'Main'`

---

<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:** [November 29, 2024, 12:46pm UTC](https://discourse.julialang.org/t/error-undefvarerror-connect-not-defined-in-main/123244/2 "2024-11-29T12:46:10Z")

</div>

The function is defined in ModelingToolkit, you are not importing ModelingToolkit

---

<div class="post-metadata">

**Author:** ![Stephen](https://avatars.discourse-cdn.com/v4/letter/s/96bed5/32.png) [@Stephen](https://discourse.julialang.org/u/Stephen)\
**Post date:** [November 29, 2024, 12:49pm UTC](https://discourse.julialang.org/t/error-undefvarerror-connect-not-defined-in-main/123244/3 "2024-11-29T12:49:10Z")

</div>

sorry, forgot change the code, same error as before

---

<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:** [November 29, 2024, 1:45pm UTC](https://discourse.julialang.org/t/error-undefvarerror-connect-not-defined-in-main/123244/4 "2024-11-29T13:45:21Z")

</div>

Have you gotten a warning in the REPL about a name conflict? Try defining

```julia
connect = ModelingToolkit.connect

```