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fix reorder_unknowns #3833

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Merged
merged 2 commits into from
Jul 22, 2025
Merged

fix reorder_unknowns #3833

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2cc32a5
fix `reorder_unknowns`
baggepinnen Jul 21, 2025
73227f0
format
baggepinnen Jul 21, 2025
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2 changes: 1 addition & 1 deletion src/linearization.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -852,7 +852,7 @@ function reorder_unknowns(sys::NamedTuple, old, new)
issorted(perm) && return sys # shortcut return, no reordering
P = zeros(Int, nx, nx)
for i in 1:nx # Build permutation matrix
P[i, perm[i]] = 1
P[perm[i], i] = 1
end
similarity_transform(sys, P; unitary = true)
end
20 changes: 20 additions & 0 deletions test/linearize.jl
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@@ -1,6 +1,26 @@
using ModelingToolkit, ADTypes, Test
using CommonSolve: solve

# Test reorder_unknowns
# sys = ssrand(1,1,4);
mats = let
A = [-1.617708540405859 0.14199864151523162 1.8120551022076838 -1.246419696614408;
0.6704209450894298 -2.4251566699889575 0.6782529705706082 -1.3731519847672025;
-0.09336677360807291 -0.11211714788917712 -3.6877851408229523 -0.7073967284605489;
-1.1743200892334098 1.1808779444006103 1.5721685015907167 -0.10858833182921268]
B = [-0.3286766047686936; -1.8473436385672866; -2.4092567234250954; -0.06371974677173559;;]
C = [-0.7144567541084362 0.18898849455229796 0.023473101245754475 1.0369097263843963]
D = [0.6397583934617636;;]
(; A, B, C, D)
end
@variables x1 x2 x3 x4
new = [x4, x1, x3, x2]
old = [x1, x2, x3, x4]
lsys = ModelingToolkit.reorder_unknowns(mats, old, new)
P = [0 1 0 0; 0 0 0 1; 0 0 1 0; 1 0 0 0]
@test isequal(P*new, old)
@test lsys.A == ModelingToolkit.similarity_transform(mats, P).A

# r is an input, and y is an output.
@independent_variables t
@variables x(t)=0 y(t)=0 u(t)=0 r(t)=0
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