FBDF not taking any timesteps except at the start and end on RLC circuit #2152
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I minimized this slightly: using OrdinaryDiffEq
using ModelingToolkitStandardLibrary.Electrical, ModelingToolkit, OrdinaryDiffEq
using ModelingToolkitStandardLibrary.Blocks: Constant, Sine
connections = Equation[]
add_conn!(x) = (push!(connections, x); x) # to match spice we want to interleave connections and declarations
systems = ODESystem[]
add_system!(x) = (push!(systems, x); x)
@named ground = Ground()
add_system!(ground)
@named Src = Sine(amplitude=1, frequency=100e6)
add_system!(Src)
@named Vsin = Voltage()
add_system!(Vsin)
connect(Src.output, Vsin.V) |> add_conn!
connect(Vsin.n, ground.g) |> add_conn!
@named Rsrc = Resistor(R=250)
add_system!(Rsrc)
connect(Rsrc.n, Vsin.p) |> add_conn!
c_match = 1.5e-12
l_match = 400e-9
@named Lmatch = Inductor(L=l_match)
add_system!(Lmatch)
connect(Rsrc.p, Lmatch.n) |> add_conn!
@named Cmatch = Capacitor(C=c_match)
add_system!(Cmatch)
connect(Rsrc.p, Cmatch.p) |> add_conn!
connect(ground.g, Cmatch.n) |> add_conn!
function TransmissionLineSegment!(_vin, _ii)
l=0.05e-9
c=0.02e-12
L1 = Inductor(L=l, name=Symbol(:L1_, _ii)) |> add_system!
_vout = L1.p
connect(_vin, L1.n) |> add_conn!
C1 = Capacitor(C=c, name=Symbol(:C1_, _ii)) |> add_system!
connect(C1.n, ground.g) |> add_conn!
connect(C1.p, _vout) |> add_conn!
return _vout
end
vout = TransmissionLineSegment!(Lmatch.p, 1)
# vout = Lmatch.p
@named Rload = Resistor(R=50)
add_system!(Rload)
connect(Rload.n, ground.g) |> add_conn!
connect(Rload.p, vout) |> add_conn!
@variables t
@named imp_model = ODESystem(connections, t ;systems)
sys = structural_simplify(imp_model)
prob = ODEProblem(sys, Pair[], (0.0, 4e-8),)
sol = solve(prob, FBDF())Note the commented-out line I added; if we drop the 
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@oscardssmith suggested I check whether setting |
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As mentioned in our chat, it's just from hitting the fundamental frequency. Anything that's not exactly a multiple of 1e-8 will work fine. using Plots
sol = solve(prob, FBDF(), dt = 1.000001e-8)
plot(sol)
It's a very special case that only comes up if you just happen to hit all zeros in the derivative estimates. |
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Describe the bug 🐞
I have created a circuit in MSL representing a transmision line with an end point dampening and solved it with FBDF.
The output is just a single line segement, with just times recorded for start and end.
This is wrong as I know the circuit solves (e.g with Rodas5P or IDA) to give a sinusioid.
Expected behavior
Solution should be a siniusoid and should match other solves
Minimal Reproducible Example 👇
Sorry it is not yet minimized
Error & Stacktrace⚠️
See only 2 versions
Environment (please complete the following information):
using Pkg; Pkg.status()using Pkg; Pkg.status(; mode = PKGMODE_MANIFEST)The text was updated successfully, but these errors were encountered: