Makestate_name work for arbitrary expressions

Project.toml

@@ -1,7 +1,7 @@
 name = "DynamicalSystemsBase"
 uuid = "6e36e845-645a-534a-86f2-f5d4aa5a06b4"
 repo = "https://github.com/JuliaDynamics/DynamicalSystemsBase.jl.git"
-version = "3.8.2"
+version = "3.8.3"
 
 [deps]
 ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"

src/core/dynamicalsystem_interface.jl

@@ -189,6 +189,9 @@ Return the state `u` of `ds` _observed_ at "index" `i`. Possibilities are:
    such as a `Num` or `Symbol` instance with the name of the symbolic variable.
    In this case, a last fourth optional positional argument `t` defaults to
    `current_time(ds)` and is the time to observe the state at.
+- Any symbolic expression involving variables present in the symbolic
+  variables tracked by the system, e.g., `i = x^2 - y` with `x, y`
+  symbolic variables.
 
 For [`ProjectedDynamicalSystem`](@ref), this function assumes that the
 state of the system is the full state space state, not the projected one

src/core/pretty_printing.jl

@@ -80,7 +80,18 @@ Return a name that matches the outcome of [`observe_state`](@ref) with `index`.
 state_name(f::Int) = "u"*subscript(f)
 state_name(f::Function) = string(f)
 state_name(f::Union{AbstractString,Symbol}) = string(f)
-state_name(f) = string(DynamicalSystemsBase.SymbolicIndexingInterface.getname(f))
+function state_name(f)
+    # First, try a symbolic name
+    try
+        n = string(DynamicalSystemsBase.SymbolicIndexingInterface.getname(f))
+        return n
+    catch e
+    end
+    # if it failed, cast into string
+    n = string(f)
+    # and remove `(t)`
+    replace(n, "(t)" => "")
+end
 
 """
     parameter_name(index)::String