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refactor: use IRInfo and IRStructure for full_equations #4525

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refactor: use IRInfo and IRStructure for full_equations #4525

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fc3db87
refactor: use `IRInfo` and `IRStructure` for `full_equations`
AayushSabharwal May 12, 2026
338e20f
fix: do not mutate decomposition subsystems in `SCCNonlinearProblem`
AayushSabharwal May 13, 2026
dfb8ad1
test: minor test update to account for new `full_equations`
AayushSabharwal May 15, 2026
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14 changes: 14 additions & 0 deletions lib/ModelingToolkitBase/src/systems/abstractsystem.jl
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Expand Up @@ -1998,6 +1998,20 @@ equations during `mtkcompile`. These equations matches generated numerical code.
See also [`equations`](@ref) and [`ModelingToolkitBase.get_eqs`](@ref).
"""
function full_equations(sys::AbstractSystem; simplify = false)
subsys = get_systems(sys)
# Fast path using `IRInfo`
if isempty(subsys)
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@oscardssmith oscardssmith May 13, 2026

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why can we only do this if we don't have subsytems? Is that fixable?

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@AayushSabharwal AayushSabharwal May 13, 2026

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I'll add a comment. get_ir_info will build the IRInfo if a cached one does not exist. Doing so requires the ParameterBindingsGraph, which is only valid for flattened systems. I'll add a comment.

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@oscardssmith oscardssmith May 13, 2026

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how hard would it be to remove that restriction? The bifurcation here seems sub-optimal.

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@AayushSabharwal AayushSabharwal May 14, 2026

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Probably not very hard, but it doesn't matter much. We hit the slow path for hierarchical systems, which we can't simulate anyway. The only case where full_equations on a hierarchical system matters is if the user is directly building a system that they will complete and never mtkcompile. It's safe to assume those systems are few and far between, and not large enough for the speedup here to matter. Flattening the system will also invalidate the cached IRInfo, so we'll redo this anyway.

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@oscardssmith oscardssmith May 14, 2026

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fair enough. I'm just coming at this from a code simplicity perspective, but I'm fine with this as is.

new_eqs = Equation[]
eqs = equations(sys)
sizehint!(new_eqs, length(eqs))
info = get_ir_info(sys)
ir = get_irstructure(sys)
@assert length(info.eqs_idxs) == length(eqs)
for (eq, rhs_idx) in zip(eqs, info.eqs_idxs)
push!(new_eqs, eq.lhs ~ ir[rhs_idx])
end
return new_eqs
end
empty_substitutions(sys) && return equations(sys)
subs = get_substitutions(sys)
neweqs = map(equations(sys)) do eq
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4 changes: 1 addition & 3 deletions lib/ModelingToolkitBase/test/serialization.jl
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Expand Up @@ -29,8 +29,7 @@ str = String(take!(io))

sys = include_string(@__MODULE__, str)
rc2 = expand_connections(rc_model)
@test isapprox(sys, rc2)
@test issetequal(equations(sys), equations(rc2))
@test issetequal(full_equations(sys), full_equations(rc2))
@test issetequal(unknowns(sys), unknowns(rc2))
@test issetequal(parameters(sys), parameters(rc2))

Expand All @@ -54,5 +53,4 @@ sol_ = solve(prob_, ImplicitEuler())
probexpr = ODEProblem{true}(ss, [capacitor.v => 0.0], (0, 0.1); expr = Val{true}, missing_guess_value);
prob_obs = eval(probexpr)
sol_obs = solve(prob_obs, ImplicitEuler())
@show all_obs
@test sol_obs[all_obs] == sol[all_obs]
6 changes: 5 additions & 1 deletion src/problems/sccnonlinearproblem.jl
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Expand Up @@ -296,7 +296,10 @@ function build_caches!(sys::System, decomposition::SCCDecomposition)
push!(banned_vars, split_indexed_var(u)[1])
end

_eqs = get_eqs(subsys)
# While we own the system and so mutation _should_ be safe, `IRInfo` exists.
# It stores the indices corresponding to equations in the `IRStructure`, which
# would be incorrect if we mutate.
_eqs = copy(get_eqs(subsys))
exprs_to_search = SymbolicT[]
for i in eachindex(_eqs)
push!(exprs_to_search, _eqs[i].rhs)
Expand All @@ -306,6 +309,7 @@ function build_caches!(sys::System, decomposition::SCCDecomposition)
for i in eachindex(_eqs)
_eqs[i] = _eqs[i].lhs ~ subber(_eqs[i].rhs)
end
subsys = decomposition.subsystems[i] = ConstructionBase.setproperties(subsys; eqs = _eqs)

if decomposition.islinear[i]
store_to_mutable_cache!(subsys, CachedLinearAb, nothing)
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