# What's wrong with this system/circuit?

**URL:** <https://discourse.julialang.org/t/whats-wrong-with-this-system-circuit/93569>\
**Category:** Modelling & Simulations\
**Tags:** modelingtoolkit\
**Created:** [January 26, 2023, 11:45am UTC](https://discourse.julialang.org/t/whats-wrong-with-this-system-circuit/93569 "2023-01-26T11:45:44Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![sh2pro](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sh2pro/32/45915_2.png) [@sh2pro](https://discourse.julialang.org/u/sh2pro)\
**Post date:** [January 26, 2023, 11:45am UTC](https://discourse.julialang.org/t/whats-wrong-with-this-system-circuit/93569/1 "2023-01-26T11:45:44Z")

</div>

I’ve defined a system as follows:

```julia
using ModelingToolkit, ModelingToolkitStandardLibrary
using DifferentialEquations
using ModelingToolkitStandardLibrary.Electrical
using ModelingToolkitStandardLibrary.Blocks

function Component(; name, R)
    @named n = Pin()
    @named p1 = Pin()
    @named p2 = Pin()
    @named R = Resistor(R=R)
    @named C = Capacitor(C=R)
    eqs = [
        connect(p1, R.p)
        connect(p2, C.p)
        connect(n, R.n, C.n)
        ]
    return ODESystem(eqs, t, [], [] ; name, 
                systems=[p1, p2, n, R, C])
end

function S(;name, num)
    # construct the layers from the center out
    comps = Vector{Any}(undef, num)
    Ra_l = Vector{Any}(undef, num)
    Ra_r = Vector{Any}(undef, num)
    Rc_l = Vector{Any}(undef, num)
    Rc_r = Vector{Any}(undef, num)
    for i in 1:num
        comps[i] = Component(; name=Symbol(:L_, i), R=1)
        Ra_l[i] = Resistor(name=Symbol(:Ra_, i, :l), R=2)
        Ra_r[i] = Resistor(name=Symbol(:Ra_, i, :r), R=3)
        Rc_l[i] = Resistor(name=Symbol(:Rc_, i, :l), R=4)
        Rc_r[i] = Resistor(name=Symbol(:Rc_, i, :r), R=5)
    end
    
    @named n = Pin()
    @named p = Pin()
    # connect everything
    eqs = [
        connect(Ra_l[1].p, Ra_r[1].p, p)
        connect(Rc_l[1].n, Rc_r[1].n, n)
        [connect(Ra_l[i].n, Ra_l[i+1].p) for i in 1:num-1]...
        [connect(Ra_r[i].n, Ra_r[i+1].p) for i in 1:num-1]...
        [connect(Rc_l[i].n, Rc_l[i+1].p) for i in 1:num-1]...
        [connect(Rc_r[i].n, Rc_r[i+1].p) for i in 1:num-1]...
        
        [connect(Ra_l[i].n, comps[i].p1) for i in 1:num]...
        [connect(Ra_r[i].n, comps[i].p2) for i in 1:num]...
        [connect(Rc_l[i].n, Rc_r[i].n, comps[i].n) for i in 1:num]...
        ]

    return ODESystem(eqs, t, [], [] ; name, 
                systems=[p, n, comps..., Ra_l..., Ra_r..., Rc_l..., Rc_r...])
end

@variables t
@named source = Voltage()
@named c = Constant(k=0.01)
@named ground = Ground()
@named s = S(num=2)

rc_eqs = [
        connect(c.output, source.V)
        connect(source.p, s.p)
        connect(s.n, source.n, ground.g)
        ]

@named rc_model = ODESystem(rc_eqs, t, systems=[s, c, source, ground])
sys = structural_simplify(rc_model)

```

No issues so far.

However, once I increase `num` to 3:

```julia
@named s = S(num=3)

```

I’m told the system is unbalanced:

```plaintext
ExtraEquationsSystemException: The system is unbalanced. There are 41 highest order derivative variables and 42 equations.
More equations than variables, here are the potential extra equation(s):
 0 ~ -s₊L_3₊n₊i(t) - s₊Ra_3l₊i(t) - s₊Ra_3r₊i(t)

```

I can’t really see what’s wrong here.  
ModelingToolkit is v8.36.0 and ModelingToolkitStandardLibrary is v1.10.0

Thanks

---

<div class="post-metadata">

**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [January 26, 2023, 7:20pm UTC](https://discourse.julialang.org/t/whats-wrong-with-this-system-circuit/93569/2 "2023-01-26T19:20:03Z")

</div>

Print out the list of equations, that would be an easier way to look at this. There’s likely just one redundancy in there.

---

<div class="post-metadata">

**Author:** ![sh2pro](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sh2pro/32/45915_2.png) [@sh2pro](https://discourse.julialang.org/u/sh2pro)\
**Post date:** [January 26, 2023, 7:47pm UTC](https://discourse.julialang.org/t/whats-wrong-with-this-system-circuit/93569/3 "2023-01-26T19:47:16Z")

</div>

Here are the equations:

```julia
julia> equations(rc_model)
connect(c.output, source.V)
connect(source.p, s.p)
connect(s.n, source.n, ground.g)
connect(Ra_1l.p, Ra_1r.p, p)
connect(Rc_1l.n, Rc_1r.n, n)
connect(Ra_1l.n, Ra_2l.p)
connect(Ra_2l.n, Ra_3l.p)
connect(Ra_1r.n, Ra_2r.p)
connect(Ra_2r.n, Ra_3r.p)
connect(Rc_1l.n, Rc_2l.p)
connect(Rc_2l.n, Rc_3l.p)
connect(Rc_1r.n, Rc_2r.p)
connect(Rc_2r.n, Rc_3r.p)
connect(Ra_1l.n, L_1.p1)
connect(Ra_2l.n, L_2.p1)
connect(Ra_3l.n, L_3.p1)
connect(Ra_1r.n, L_1.p2)
connect(Ra_2r.n, L_2.p2)
connect(Ra_3r.n, L_3.p2)
connect(Rc_1l.n, Rc_1r.n, L_1.n)
connect(Rc_2l.n, Rc_2r.n, L_2.n)
connect(Rc_3l.n, Rc_3r.n, L_3.n)
connect(p1, R.p)
connect(p2, C.p)
connect(n, R.n, C.n)
s₊L_1₊R₊v(t) ~ s₊L_1₊R₊p₊v(t) - s₊L_1₊R₊n₊v(t)
0 ~ s₊L_1₊R₊n₊i(t) + s₊L_1₊R₊p₊i(t)
s₊L_1₊R₊i(t) ~ s₊L_1₊R₊p₊i(t)
s₊L_1₊R₊v(t) ~ s₊L_1₊R₊R*s₊L_1₊R₊i(t)
s₊L_1₊C₊v(t) ~ s₊L_1₊C₊p₊v(t) - s₊L_1₊C₊n₊v(t)
0 ~ s₊L_1₊C₊n₊i(t) + s₊L_1₊C₊p₊i(t)
s₊L_1₊C₊i(t) ~ s₊L_1₊C₊p₊i(t)
Differential(t)(s₊L_1₊C₊v(t)) ~ s₊L_1₊C₊i(t) / s₊L_1₊C₊C
connect(p1, R.p)
connect(p2, C.p)
connect(n, R.n, C.n)
s₊L_2₊R₊v(t) ~ s₊L_2₊R₊p₊v(t) - s₊L_2₊R₊n₊v(t)
0 ~ s₊L_2₊R₊n₊i(t) + s₊L_2₊R₊p₊i(t)
s₊L_2₊R₊i(t) ~ s₊L_2₊R₊p₊i(t)
s₊L_2₊R₊v(t) ~ s₊L_2₊R₊R*s₊L_2₊R₊i(t)
s₊L_2₊C₊v(t) ~ s₊L_2₊C₊p₊v(t) - s₊L_2₊C₊n₊v(t)
0 ~ s₊L_2₊C₊n₊i(t) + s₊L_2₊C₊p₊i(t)
s₊L_2₊C₊i(t) ~ s₊L_2₊C₊p₊i(t)
Differential(t)(s₊L_2₊C₊v(t)) ~ s₊L_2₊C₊i(t) / s₊L_2₊C₊C
connect(p1, R.p)
connect(p2, C.p)
connect(n, R.n, C.n)
s₊L_3₊R₊v(t) ~ s₊L_3₊R₊p₊v(t) - s₊L_3₊R₊n₊v(t)
0 ~ s₊L_3₊R₊n₊i(t) + s₊L_3₊R₊p₊i(t)
s₊L_3₊R₊i(t) ~ s₊L_3₊R₊p₊i(t)
s₊L_3₊R₊v(t) ~ s₊L_3₊R₊R*s₊L_3₊R₊i(t)
s₊L_3₊C₊v(t) ~ s₊L_3₊C₊p₊v(t) - s₊L_3₊C₊n₊v(t)
0 ~ s₊L_3₊C₊n₊i(t) + s₊L_3₊C₊p₊i(t)
s₊L_3₊C₊i(t) ~ s₊L_3₊C₊p₊i(t)
Differential(t)(s₊L_3₊C₊v(t)) ~ s₊L_3₊C₊i(t) / s₊L_3₊C₊C
s₊Ra_1l₊v(t) ~ s₊Ra_1l₊p₊v(t) - s₊Ra_1l₊n₊v(t)
0 ~ s₊Ra_1l₊n₊i(t) + s₊Ra_1l₊p₊i(t)
s₊Ra_1l₊i(t) ~ s₊Ra_1l₊p₊i(t)
s₊Ra_1l₊v(t) ~ s₊Ra_1l₊R*s₊Ra_1l₊i(t)
s₊Ra_2l₊v(t) ~ s₊Ra_2l₊p₊v(t) - s₊Ra_2l₊n₊v(t)
0 ~ s₊Ra_2l₊n₊i(t) + s₊Ra_2l₊p₊i(t)
s₊Ra_2l₊i(t) ~ s₊Ra_2l₊p₊i(t)
s₊Ra_2l₊v(t) ~ s₊Ra_2l₊R*s₊Ra_2l₊i(t)
s₊Ra_3l₊v(t) ~ s₊Ra_3l₊p₊v(t) - s₊Ra_3l₊n₊v(t)
0 ~ s₊Ra_3l₊n₊i(t) + s₊Ra_3l₊p₊i(t)
s₊Ra_3l₊i(t) ~ s₊Ra_3l₊p₊i(t)
s₊Ra_3l₊v(t) ~ s₊Ra_3l₊R*s₊Ra_3l₊i(t)
s₊Ra_1r₊v(t) ~ s₊Ra_1r₊p₊v(t) - s₊Ra_1r₊n₊v(t)
0 ~ s₊Ra_1r₊n₊i(t) + s₊Ra_1r₊p₊i(t)
s₊Ra_1r₊i(t) ~ s₊Ra_1r₊p₊i(t)
s₊Ra_1r₊v(t) ~ s₊Ra_1r₊R*s₊Ra_1r₊i(t)
s₊Ra_2r₊v(t) ~ s₊Ra_2r₊p₊v(t) - s₊Ra_2r₊n₊v(t)
0 ~ s₊Ra_2r₊n₊i(t) + s₊Ra_2r₊p₊i(t)
s₊Ra_2r₊i(t) ~ s₊Ra_2r₊p₊i(t)
s₊Ra_2r₊v(t) ~ s₊Ra_2r₊R*s₊Ra_2r₊i(t)
s₊Ra_3r₊v(t) ~ s₊Ra_3r₊p₊v(t) - s₊Ra_3r₊n₊v(t)
0 ~ s₊Ra_3r₊n₊i(t) + s₊Ra_3r₊p₊i(t)
s₊Ra_3r₊i(t) ~ s₊Ra_3r₊p₊i(t)
s₊Ra_3r₊v(t) ~ s₊Ra_3r₊R*s₊Ra_3r₊i(t)
s₊Rc_1l₊v(t) ~ s₊Rc_1l₊p₊v(t) - s₊Rc_1l₊n₊v(t)
0 ~ s₊Rc_1l₊n₊i(t) + s₊Rc_1l₊p₊i(t)
s₊Rc_1l₊i(t) ~ s₊Rc_1l₊p₊i(t)
s₊Rc_1l₊v(t) ~ s₊Rc_1l₊R*s₊Rc_1l₊i(t)
s₊Rc_2l₊v(t) ~ s₊Rc_2l₊p₊v(t) - s₊Rc_2l₊n₊v(t)
0 ~ s₊Rc_2l₊n₊i(t) + s₊Rc_2l₊p₊i(t)
s₊Rc_2l₊i(t) ~ s₊Rc_2l₊p₊i(t)
s₊Rc_2l₊v(t) ~ s₊Rc_2l₊R*s₊Rc_2l₊i(t)
s₊Rc_3l₊v(t) ~ s₊Rc_3l₊p₊v(t) - s₊Rc_3l₊n₊v(t)
0 ~ s₊Rc_3l₊n₊i(t) + s₊Rc_3l₊p₊i(t)
s₊Rc_3l₊i(t) ~ s₊Rc_3l₊p₊i(t)
s₊Rc_3l₊v(t) ~ s₊Rc_3l₊R*s₊Rc_3l₊i(t)
s₊Rc_1r₊v(t) ~ s₊Rc_1r₊p₊v(t) - s₊Rc_1r₊n₊v(t)
0 ~ s₊Rc_1r₊n₊i(t) + s₊Rc_1r₊p₊i(t)
s₊Rc_1r₊i(t) ~ s₊Rc_1r₊p₊i(t)
s₊Rc_1r₊v(t) ~ s₊Rc_1r₊R*s₊Rc_1r₊i(t)
s₊Rc_2r₊v(t) ~ s₊Rc_2r₊p₊v(t) - s₊Rc_2r₊n₊v(t)
0 ~ s₊Rc_2r₊n₊i(t) + s₊Rc_2r₊p₊i(t)
s₊Rc_2r₊i(t) ~ s₊Rc_2r₊p₊i(t)
s₊Rc_2r₊v(t) ~ s₊Rc_2r₊R*s₊Rc_2r₊i(t)
s₊Rc_3r₊v(t) ~ s₊Rc_3r₊p₊v(t) - s₊Rc_3r₊n₊v(t)
0 ~ s₊Rc_3r₊n₊i(t) + s₊Rc_3r₊p₊i(t)
s₊Rc_3r₊i(t) ~ s₊Rc_3r₊p₊i(t)
s₊Rc_3r₊v(t) ~ s₊Rc_3r₊R*s₊Rc_3r₊i(t)
c₊output₊u(t) ~ c₊k
source₊v(t) ~ source₊p₊v(t) - source₊n₊v(t)
0 ~ source₊n₊i(t) + source₊p₊i(t)
source₊i(t) ~ source₊p₊i(t)
source₊v(t) ~ source₊V₊u(t)
ground₊g₊v(t) ~ 0

```

PNG of the Latex

 ![eqs](https://global.discourse-cdn.com/julialang/original/3X/6/5/65417176b0456b543387830ada66e926f12c1e82.png)

---

<div class="post-metadata">

**Author:** ![sh2pro](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sh2pro/32/45915_2.png) [@sh2pro](https://discourse.julialang.org/u/sh2pro)\
**Post date:** [January 26, 2023, 7:50pm UTC](https://discourse.julialang.org/t/whats-wrong-with-this-system-circuit/93569/4 "2023-01-26T19:50:51Z")

</div>

states:

```julia
s₊p₊v(t)
s₊p₊i(t)
s₊n₊v(t)
s₊n₊i(t)
s₊L_1₊p1₊v(t)
s₊L_1₊p1₊i(t)
s₊L_1₊p2₊v(t)
s₊L_1₊p2₊i(t)
s₊L_1₊n₊v(t)
s₊L_1₊n₊i(t)
s₊L_1₊R₊v(t)
s₊L_1₊R₊i(t)
s₊L_1₊R₊p₊v(t)
s₊L_1₊R₊p₊i(t)
s₊L_1₊R₊n₊v(t)
s₊L_1₊R₊n₊i(t)
s₊L_1₊C₊v(t)
s₊L_1₊C₊i(t)
s₊L_1₊C₊p₊v(t)
s₊L_1₊C₊p₊i(t)
s₊L_1₊C₊n₊v(t)
s₊L_1₊C₊n₊i(t)
s₊L_2₊p1₊v(t)
s₊L_2₊p1₊i(t)
s₊L_2₊p2₊v(t)
s₊L_2₊p2₊i(t)
s₊L_2₊n₊v(t)
s₊L_2₊n₊i(t)
s₊L_2₊R₊v(t)
s₊L_2₊R₊i(t)
s₊L_2₊R₊p₊v(t)
s₊L_2₊R₊p₊i(t)
s₊L_2₊R₊n₊v(t)
s₊L_2₊R₊n₊i(t)
s₊L_2₊C₊v(t)
s₊L_2₊C₊i(t)
s₊L_2₊C₊p₊v(t)
s₊L_2₊C₊p₊i(t)
s₊L_2₊C₊n₊v(t)
s₊L_2₊C₊n₊i(t)
s₊L_3₊p1₊v(t)
s₊L_3₊p1₊i(t)
s₊L_3₊p2₊v(t)
s₊L_3₊p2₊i(t)
s₊L_3₊n₊v(t)
s₊L_3₊n₊i(t)
s₊L_3₊R₊v(t)
s₊L_3₊R₊i(t)
s₊L_3₊R₊p₊v(t)
s₊L_3₊R₊p₊i(t)
s₊L_3₊R₊n₊v(t)
s₊L_3₊R₊n₊i(t)
s₊L_3₊C₊v(t)
s₊L_3₊C₊i(t)
s₊L_3₊C₊p₊v(t)
s₊L_3₊C₊p₊i(t)
s₊L_3₊C₊n₊v(t)
s₊L_3₊C₊n₊i(t)
s₊Ra_1l₊v(t)
s₊Ra_1l₊i(t)
s₊Ra_1l₊p₊v(t)
s₊Ra_1l₊p₊i(t)
s₊Ra_1l₊n₊v(t)
s₊Ra_1l₊n₊i(t)
s₊Ra_2l₊v(t)
s₊Ra_2l₊i(t)
s₊Ra_2l₊p₊v(t)
s₊Ra_2l₊p₊i(t)
s₊Ra_2l₊n₊v(t)
s₊Ra_2l₊n₊i(t)
s₊Ra_3l₊v(t)
s₊Ra_3l₊i(t)
s₊Ra_3l₊p₊v(t)
s₊Ra_3l₊p₊i(t)
s₊Ra_3l₊n₊v(t)
s₊Ra_3l₊n₊i(t)
s₊Ra_1r₊v(t)
s₊Ra_1r₊i(t)
s₊Ra_1r₊p₊v(t)
s₊Ra_1r₊p₊i(t)
s₊Ra_1r₊n₊v(t)
s₊Ra_1r₊n₊i(t)
s₊Ra_2r₊v(t)
s₊Ra_2r₊i(t)
s₊Ra_2r₊p₊v(t)
s₊Ra_2r₊p₊i(t)
s₊Ra_2r₊n₊v(t)
s₊Ra_2r₊n₊i(t)
s₊Ra_3r₊v(t)
s₊Ra_3r₊i(t)
s₊Ra_3r₊p₊v(t)
s₊Ra_3r₊p₊i(t)
s₊Ra_3r₊n₊v(t)
s₊Ra_3r₊n₊i(t)
s₊Rc_1l₊v(t)
s₊Rc_1l₊i(t)
s₊Rc_1l₊p₊v(t)
s₊Rc_1l₊p₊i(t)
s₊Rc_1l₊n₊v(t)
s₊Rc_1l₊n₊i(t)
s₊Rc_2l₊v(t)
s₊Rc_2l₊i(t)
s₊Rc_2l₊p₊v(t)
s₊Rc_2l₊p₊i(t)
s₊Rc_2l₊n₊v(t)
s₊Rc_2l₊n₊i(t)
s₊Rc_3l₊v(t)
s₊Rc_3l₊i(t)
s₊Rc_3l₊p₊v(t)
s₊Rc_3l₊p₊i(t)
s₊Rc_3l₊n₊v(t)
s₊Rc_3l₊n₊i(t)
s₊Rc_1r₊v(t)
s₊Rc_1r₊i(t)
s₊Rc_1r₊p₊v(t)
s₊Rc_1r₊p₊i(t)
s₊Rc_1r₊n₊v(t)
s₊Rc_1r₊n₊i(t)
s₊Rc_2r₊v(t)
s₊Rc_2r₊i(t)
s₊Rc_2r₊p₊v(t)
s₊Rc_2r₊p₊i(t)
s₊Rc_2r₊n₊v(t)
s₊Rc_2r₊n₊i(t)
s₊Rc_3r₊v(t)
s₊Rc_3r₊i(t)
s₊Rc_3r₊p₊v(t)
s₊Rc_3r₊p₊i(t)
s₊Rc_3r₊n₊v(t)
s₊Rc_3r₊n₊i(t)
c₊output₊u(t)
source₊v(t)
source₊i(t)
source₊p₊v(t)
source₊p₊i(t)
source₊n₊v(t)
source₊n₊i(t)
source₊V₊u(t)
ground₊g₊v(t)
ground₊g₊i(t)

```

---

<div class="post-metadata">

**Author:** ![YingboMa](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yingboma/32/2181_2.png) [@YingboMa](https://discourse.julialang.org/u/YingboMa)\
**Post date:** [January 30, 2023, 12:02am UTC](https://discourse.julialang.org/t/whats-wrong-with-this-system-circuit/93569/5 "2023-01-30T00:02:36Z")

</div>

It hard for me to see what’s wrong without a diagram. But removing

> [@sh2pro](#):
>
> ```julia
> [connect(Rc_l[i].n, Rc_r[i].n, comps[i].n) for i in 1:num]...
> 
> ```

makes the system balanced. Also, you are accidentally overwriting `R`. It should be

```julia
function Component(; name, R)
    @named n = Pin()
    @named p1 = Pin()
    @named p2 = Pin()
    vR = R
    @named R = Resistor(R=vR)
    @named C = Capacitor(C=vR)
    eqs = [
        connect(p1, R.p)
        connect(p2, C.p)
        connect(n, R.n, C.n)
        ]
    return ODESystem(eqs, t, [], [] ; name, 
                systems=[p1, p2, n, R, C])
end

```

---

<div class="post-metadata">

**Author:** ![sh2pro](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sh2pro/32/45915_2.png) [@sh2pro](https://discourse.julialang.org/u/sh2pro)\
**Post date:** [January 30, 2023, 11:03am UTC](https://discourse.julialang.org/t/whats-wrong-with-this-system-circuit/93569/6 "2023-01-30T11:03:03Z")

</div>

Thanks!  
`Rc_l[1].n` and `Rc_r[1].n` do appear both in

```julia
connect(Rc_l[1].n, Rc_r[1].n, n)

```

and in

```julia
[connect(Rc_l[i].n, Rc_r[i].n, comps[i].n) for i in 1:num]...

```

Replacing the first with:

```julia
connect(Rc_l[1].n, n)

```

seems to fix this issue.

This removes:

```julia
connect(Rc_l[1].n, Rc_r[1].n) 

```

which already appears in the 2nd line.

So, yes, there’s an extra equation. However, there isn’t any actual inconsistency here: the same equation appears twice. This seems like something `ModelingToolkit` can detect and ignore.

---

<div class="post-metadata">

**Author:** ![sh2pro](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sh2pro/32/45915_2.png) [@sh2pro](https://discourse.julialang.org/u/sh2pro)\
**Post date:** [January 30, 2023, 11:10am UTC](https://discourse.julialang.org/t/whats-wrong-with-this-system-circuit/93569/7 "2023-01-30T11:10:32Z")

</div>

PS:  
the line

```julia
prob = ODAEProblem(sys, Pair[], (0, 10))

```

[fails](https://github.com/SciML/ModelingToolkit.jl/issues/2053)

---

<div class="post-metadata">

**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [January 30, 2023, 11:52am UTC](https://discourse.julialang.org/t/whats-wrong-with-this-system-circuit/93569/8 "2023-01-30T11:52:08Z")

</div>

> [@sh2pro](#):
>
> However, there isn’t any actual inconsistency here: the same equation appears twice. This seems like something `ModelingToolkit` can detect and ignore.

Open an issue. I do think a good default behavior would be to detect and warn, with options to detect and error or ignore, but of course that would need to be added.