clarify in obserrve state that you can give any state vector

Author: Datseris

Project.toml

@@ -1,7 +1,7 @@
 name = "DynamicalSystemsBase"
 uuid = "6e36e845-645a-534a-86f2-f5d4aa5a06b4"
 repo = "https://github.com/JuliaDynamics/DynamicalSystemsBase.jl.git"
-version = "3.5.2"
+version = "3.5.3"
 
 [deps]
 ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"

src/core/dynamicalsystem_interface.jl

@@ -163,9 +163,9 @@ See also [`initial_state`](@ref), [`observe_state`](@ref).
 current_state(ds::DynamicalSystem) = ds.u
 
 """
-    observe_state(ds::DynamicalSystem, i) → x::Real
+    observe_state(ds::DynamicalSystem, i [,u = current_state(ds)]) → x::Real
 
-Return the current state of `ds` _observed_ at "index" `i`. Possibilities are:
+Return the state `u` of `ds` _observed_ at "index" `i`. Possibilities are:
 
 - `i::Int` returns the `i`-th dynamic variable.
 - `i::Function` returns `f(current_state(ds))`, which is asserted to be a real number.