Use initialization_equations in flatten

Author: YingboMa

src/systems/abstractsystem.jl

@@ -879,7 +879,8 @@ function namespace_equation(eq::Equation,
     _lhs ~ _rhs
 end
 
-function namespace_initialization_equations(sys::AbstractSystem, ivs = independent_variables(sys))
+function namespace_initialization_equations(
+        sys::AbstractSystem, ivs = independent_variables(sys))
     eqs = initialization_equations(sys)
     isempty(eqs) && return Equation[]
     map(eq -> namespace_equation(eq, sys; ivs), eqs)

src/systems/diffeqs/abstractodesystem.jl

@@ -908,8 +908,8 @@ function process_DEProblem(constructor, sys::AbstractODESystem, u0map, parammap;
     # ModelingToolkit.get_tearing_state(sys) !== nothing => Requires structural_simplify first
     if sys isa ODESystem && build_initializeprob &&
        ((implicit_dae || !isempty(missingvars)) &&
-       all(isequal(Continuous()), ci.var_domain) &&
-       ModelingToolkit.get_tearing_state(sys) !== nothing) ||
+        all(isequal(Continuous()), ci.var_domain) &&
+        ModelingToolkit.get_tearing_state(sys) !== nothing) ||
        !isempty(initialization_equations(sys)) && t !== nothing
         if eltype(u0map) <: Number
             u0map = unknowns(sys) .=> u0map

src/systems/diffeqs/odesystem.jl

@@ -360,6 +360,7 @@ function flatten(sys::ODESystem, noeqs = false)
             discrete_events = discrete_events(sys),
             defaults = defaults(sys),
             name = nameof(sys),
+            initialization_eqs = initialization_equations(sys),
             checks = false)
     end
 end