fix: use is_diff_equation with flatten_equations

Author: vyudu

src/systems/diffeqs/odesystem.jl

@@ -305,7 +305,7 @@ function ODESystem(deqs::AbstractVector{<:Equation}, iv, dvs, ps;
         throw(ArgumentError("System names must be unique."))
     end
 
-    algeeqs = filter(eq -> eq.lhs isa Union{Symbolic, Number} && !is_diff_equation(eq), deqs)
+    algeeqs = filter(eq -> eq.lhs isa Union{Symbolic, Number} && !is_diff_equation(eq), flatten_equations(deqs))
     cont_callbacks = SymbolicContinuousCallbacks(continuous_events; algeeqs, iv)
     disc_callbacks = SymbolicDiscreteCallbacks(discrete_events; algeeqs, iv)
 

src/systems/diffeqs/sdesystem.jl

@@ -264,7 +264,7 @@ function SDESystem(deqs::AbstractVector{<:Equation}, neqs::AbstractArray, iv, dv
     Wfact = RefValue(EMPTY_JAC)
     Wfact_t = RefValue(EMPTY_JAC)
 
-    algeeqs = filter(eq -> eq.lhs isa Union{Symbolic, Number} && !is_diff_equation(eq), deqs)
+    algeeqs = filter(eq -> eq.lhs isa Union{Symbolic, Number} && !is_diff_equation(eq), flatten_equations(deqs))
     cont_callbacks = SymbolicContinuousCallbacks(continuous_events; algeeqs, iv)
     disc_callbacks = SymbolicDiscreteCallbacks(discrete_events; algeeqs, iv)
     if is_dde === nothing

src/systems/discrete_system/implicit_discrete_system.jl

@@ -292,11 +292,11 @@ function shift_u0map_forward(sys::ImplicitDiscreteSystem, u0map, defs)
         v = u0map[k]
         if !((op = operation(k)) isa Shift)
             isnothing(getunshifted(k)) &&
-                @warn "Initial condition given in term of current state of the unknown. If `build_initializeprob = false, this may be overriden by the implicit discrete solver."
+                @warn "Initial condition given in term of current state of the unknown. If `build_initializeprob = false`, this may be overriden by the implicit discrete solver."
 
             updated[k] = v
         elseif op.steps > 0
-            error("Initial conditions must be for the past state of the unknowns. Instead of providing the condition for $k, provide the condition for $(Shift(iv, -1)(only(arguments(k)))).")
+            error("Initial conditions must be for the current or past state of the unknowns. Instead of providing the condition for $k, provide the condition for $(Shift(iv, -1)(only(arguments(k)))).")
         else
             updated[k] = v
         end