refactor: handle NullParameters, fix independent_variable_symbols for…

… multivariate systems

src/systems/abstractsystem.jl

@@ -185,70 +185,72 @@ end
 #Treat the result as a vector of symbols always
 function SymbolicIndexingInterface.is_variable(sys::AbstractSystem, sym)
     if unwrap(sym) isa Int    # [x, 1] coerces 1 to a Num
-        return unwrap(sym) in 1:length(unknown_states(sys))
+        return unwrap(sym) in 1:length(variable_symbols(sys))
     end
-    return any(isequal(sym), unknown_states(sys)) || hasname(sym) && is_variable(sys, getname(sym))
+    return any(isequal(sym), variable_symbols(sys)) || hasname(sym) && is_variable(sys, getname(sym))
 end
 
 function SymbolicIndexingInterface.is_variable(sys::AbstractSystem, sym::Symbol)
-    return any(isequal(sym), getname.(unknown_states(sys))) || count('₊', string(sym)) == 1 && count(isequal(sym), Symbol.(sys.name, :₊, getname.(unknown_states(sys)))) == 1
+    return any(isequal(sym), getname.(variable_symbols(sys))) || count('₊', string(sym)) == 1 && count(isequal(sym), Symbol.(sys.name, :₊, getname.(variable_symbols(sys)))) == 1
 end
 
 function SymbolicIndexingInterface.variable_index(sys::AbstractSystem, sym)
     if unwrap(sym) isa Int
         return unwrap(sym)
     end
-    idx = findfirst(isequal(sym), unknown_states(sys))
+    idx = findfirst(isequal(sym), variable_symbols(sys))
     if idx === nothing && hasname(sym)
         idx = variable_index(sys, getname(sym))
     end
     return idx
 end
 
 function SymbolicIndexingInterface.variable_index(sys::AbstractSystem, sym::Symbol)
-    idx = findfirst(isequal(sym), getname.(unknown_states(sys)))
+    idx = findfirst(isequal(sym), getname.(variable_symbols(sys)))
     if idx !== nothing
         return idx
     elseif count('₊', string(sym)) == 1
-        return findfirst(isequal(sym), Symbol.(sys.name, :₊, getname.(unknown_states(sys))))
+        return findfirst(isequal(sym), Symbol.(sys.name, :₊, getname.(variable_symbols(sys))))
     end
     return nothing
 end
 
+SymbolicIndexingInterface.variable_symbols(sys::AbstractMultivariateSystem) = sys.dvs
+
 function SymbolicIndexingInterface.variable_symbols(sys::AbstractSystem)
     return unknown_states(sys)
 end
 
 function SymbolicIndexingInterface.is_parameter(sys::AbstractSystem, sym)
     if unwrap(sym) isa Int
-        return unwrap(sym) in 1:length(parameters(sys))
+        return unwrap(sym) in 1:length(parameter_symbols(sys))
     end
 
-    return any(isequal(sym), parameters(sys)) || hasname(sym) && is_parameter(sys, getname(sym))
+    return any(isequal(sym), parameter_symbols(sys)) || hasname(sym) && is_parameter(sys, getname(sym))
 end
 
 function SymbolicIndexingInterface.is_parameter(sys::AbstractSystem, sym::Symbol)
-    return any(isequal(sym), getname.(parameters(sys))) ||
-        count('₊', string(sym)) == 1 && count(isequal(sym), Symbol.(sys.name, :₊, getname.(parameters(sys)))) == 1
+    return any(isequal(sym), getname.(parameter_symbols(sys))) ||
+        count('₊', string(sym)) == 1 && count(isequal(sym), Symbol.(sys.name, :₊, getname.(parameter_symbols(sys)))) == 1
 end
 
 function SymbolicIndexingInterface.parameter_index(sys::AbstractSystem, sym)
     if unwrap(sym) isa Int
         return unwrap(sym)
     end
-    idx = findfirst(isequal(sym), parameters(sys))
+    idx = findfirst(isequal(sym), parameter_symbols(sys))
     if idx === nothing && hasname(sym)
         idx = parameter_index(sys, getname(sym))
     end
     return idx
 end
 
 function SymbolicIndexingInterface.parameter_index(sys::AbstractSystem, sym::Symbol)
-    idx = findfirst(isequal(sym), getname.(parameters(sys)))
+    idx = findfirst(isequal(sym), getname.(parameter_symbols(sys)))
     if idx !== nothing
         return idx
     elseif count('₊', string(sym)) == 1
-        return findfirst(isequal(sym), Symbol.(sys.name, :₊, getname.(parameters(sys))))
+        return findfirst(isequal(sym), Symbol.(sys.name, :₊, getname.(parameter_symbols(sys))))
     end
     return nothing
 end
@@ -258,7 +260,7 @@ function SymbolicIndexingInterface.parameter_symbols(sys::AbstractSystem)
 end
 
 function SymbolicIndexingInterface.is_independent_variable(sys::AbstractSystem, sym)
-    return any(isequal(sym), independent_variables(sys))
+    return any(isequal(sym), independent_variable_symbols(sys))
 end
 
 function SymbolicIndexingInterface.is_independent_variable(sys::AbstractSystem, sym::Symbol)
@@ -632,6 +634,9 @@ end
 
 function parameters(sys::AbstractSystem)
     ps = get_ps(sys)
+    if ps == SciMLBase.NullParameters()
+        return []
+    end
     systems = get_systems(sys)
     unique(isempty(systems) ? ps : [ps; reduce(vcat, namespace_parameters.(systems))])
 end