fixup! fix: create and solve initialization system in linearization_function

Author: AayushSabharwal

src/systems/abstractsystem.jl

@@ -1781,7 +1781,7 @@ function linearization_function(sys::AbstractSystem, inputs,
                     error("Number of unknown variables ($(length(sts))) does not match the number of input unknowns ($(length(u)))")
                 if initialize && !isempty(alge_idxs) # This is expensive and can be omitted if the user knows that the system is already initialized
                     initprob = NonlinearLeastSquaresProblem(initfn, u, p)
-                    @set! fun.initializeproblem = initprob
+                    @set! fun.initializeprob = initprob
                     residual = fun(u, p, t)
                     if norm(residual[alge_idxs]) > √(eps(eltype(residual)))
                         prob = ODEProblem(fun, u, (t, t + 1), p)

test/downstream/linearize.jl

@@ -120,10 +120,10 @@ lsys = ModelingToolkit.reorder_unknowns(lsys0, unknowns(ssys), desired_order)
 lsyss, _ = ModelingToolkit.linearize_symbolic(pid, [reference.u, measurement.u],
     [ctr_output.u])
 
-@test substitute(lsyss.A, ModelingToolkit.defaults(pid)) == lsys.A
-@test substitute(lsyss.B, ModelingToolkit.defaults(pid)) == lsys.B
-@test substitute(lsyss.C, ModelingToolkit.defaults(pid)) == lsys.C
-@test substitute(lsyss.D, ModelingToolkit.defaults(pid)) == lsys.D
+@test substitute(lsyss.A, merge(ModelingToolkit.defaults(pid), ModelingToolkit.guesses(pid))) == lsys.A
+@test substitute(lsyss.B, merge(ModelingToolkit.defaults(pid), ModelingToolkit.guesses(pid))) == lsys.B
+@test substitute(lsyss.C, merge(ModelingToolkit.defaults(pid), ModelingToolkit.guesses(pid))) == lsys.C
+@test substitute(lsyss.D, merge(ModelingToolkit.defaults(pid), ModelingToolkit.guesses(pid))) == lsys.D
 
 # Test with the reverse desired unknown order as well to verify that similarity transform and reoreder_unknowns really works
 lsys = ModelingToolkit.reorder_unknowns(lsys, unknowns(ssys), reverse(desired_order))