Also forward guesses in extend(), in case initialization equations are nonlinear

Author: hersle

src/systems/abstractsystem.jl

@@ -2528,18 +2528,19 @@ function extend(sys::AbstractSystem, basesys::AbstractSystem; name::Symbol = nam
     cevs = union(get_continuous_events(basesys), get_continuous_events(sys))
     devs = union(get_discrete_events(basesys), get_discrete_events(sys))
     defs = merge(get_defaults(basesys), get_defaults(sys)) # prefer `sys`
+    guesses = merge(get_guesses(basesys), get_guesses(sys)) # prefer `sys`
     ieqs = union(get_initialization_eqs(basesys), get_initialization_eqs(sys))
     syss = union(get_systems(basesys), get_systems(sys))
 
     if length(ivs) == 0
         T(eqs, sts, ps, observed = obs, defaults = defs, name = name, systems = syss,
             continuous_events = cevs, discrete_events = devs, gui_metadata = gui_metadata,
-            parameter_dependencies = dep_ps, initialization_eqs = ieqs)
+            parameter_dependencies = dep_ps, initialization_eqs = ieqs, guesses = guesses)
     elseif length(ivs) == 1
         T(eqs, ivs[1], sts, ps, observed = obs, defaults = defs, name = name,
             systems = syss, continuous_events = cevs, discrete_events = devs,
             gui_metadata = gui_metadata, parameter_dependencies = dep_ps,
-            initialization_eqs = ieqs)
+            initialization_eqs = ieqs, guesses = guesses)
     end
 end
 

test/initializationsystem.jl

@@ -448,10 +448,11 @@ unsimp = generate_initializesystem(pend; u0map = [x => 1], initialization_eqs =
 sys = structural_simplify(unsimp; fully_determined = false)
 @test length(equations(sys)) == 3
 
-# Extend two systems with initialization equations
+# Extend two systems with initialization equations and guesses
 # https://github.com/SciML/ModelingToolkit.jl/issues/2845
 @variables x(t) y(t)
 @named sysx = ODESystem([D(x) ~ 0], t; initialization_eqs = [x ~ 1])
-@named sysy = ODESystem([D(y) ~ 0], t; initialization_eqs = [y ~ 2])
+@named sysy = ODESystem([D(y) ~ 0], t; initialization_eqs = [y^2 ~ 2], guesses = [y => 1])
 sys = extend(sysx, sysy)
 @test length(equations(generate_initializesystem(sys))) == 2
+@test length(ModelingToolkit.guesses(sys)) == 1