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fix: fix simplification of empty systems #3890

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Merged
merged 1 commit into from
Aug 12, 2025
Merged

fix: fix simplification of empty systems #3890

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2 changes: 1 addition & 1 deletion src/systems/systemstructure.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -928,7 +928,7 @@ function mtkcompile!(state::TearingState; simplify = false,
time_domains = merge(Dict(state.fullvars .=> ci.var_domain),
Dict(default_toterm.(state.fullvars) .=> ci.var_domain))
tss, clocked_inputs, continuous_id, id_to_clock = ModelingToolkit.split_system(ci)
if continuous_id == 0
if !isempty(tss) && continuous_id == 0
# do a trait check here - handle fully discrete system
additional_passes = get(kwargs, :additional_passes, nothing)
if !isnothing(additional_passes) && any(discrete_compile_pass, additional_passes)
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6 changes: 6 additions & 0 deletions test/odesystem.jl
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Expand Up @@ -1628,3 +1628,9 @@ import Test: @test
@mtkbuild sys = System(D(x) ~ t, t)
@test sys isa System
end

@testset "Empty system can be simplified" begin
@named sys = System(Equation[], t)
ss = mtkcompile(sys)
@test length(equations(ss)) == length(unknowns(ss)) == 0
end
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