Add symbolic_indexing_interface

- SymbolCache and interface functions added and exported
- `states`, `parameters` and `independent_variables` hoisted down from
  MTK

Author: AayushSabharwal

src/RecursiveArrayTools.jl

@@ -25,6 +25,7 @@ abstract type AbstractVectorOfArray{T, N, A} <: AbstractArray{T, N} end
 abstract type AbstractDiffEqArray{T, N, A} <: AbstractVectorOfArray{T, N, A} end
 
 include("utils.jl")
+include("symbolic_indexing_interface.jl")
 include("vector_of_array.jl")
 include("tabletraits.jl")
 include("array_partition.jl")
@@ -36,6 +37,9 @@ import GPUArraysCore
 Base.convert(T::Type{<:GPUArraysCore.AbstractGPUArray}, VA::AbstractVectorOfArray) = T(VA)
 ChainRulesCore.rrule(T::Type{<:GPUArraysCore.AbstractGPUArray}, xs::AbstractVectorOfArray) = T(xs), ȳ -> (NoTangent(),ȳ)
 
+export independent_variables, is_indep_sym, states, state_sym_to_index, is_state_sym,
+       parameters, param_sym_to_index, is_param_sym, SymbolCache
+
 export VectorOfArray, DiffEqArray, AbstractVectorOfArray, AbstractDiffEqArray,
        AllObserved, vecarr_to_arr, vecarr_to_vectors, tuples
 

src/symbolic_indexing_interface.jl

@@ -0,0 +1,84 @@
+"""
+$(TYPEDSIGNATURES)
+
+Get the set of independent variables for the given system.
+"""
+function independent_variables end
+
+"""
+$(TYPEDSIGNATURES)
+
+Check if the given sym is an independent variable in the given system.
+"""
+function is_indep_sym end
+
+"""
+$(TYPEDSIGNATURES)
+
+Get the set of states for the given system.
+"""
+function states end
+
+"""
+$(TYPEDSIGNATURES)
+
+Find the index of the given sym in the given system.
+"""
+function state_sym_to_index end
+
+"""
+$(TYPEDSIGNATURES)
+
+Check if the given sym is a state variable in the given system.
+"""
+function is_state_sym end
+
+"""
+$(TYPEDSIGNATURES)
+
+Get the set of parameters variables for the given system.
+"""
+function parameters end
+
+"""
+$(TYPEDSIGNATURES)
+
+Find the index of the given sym in the given system.
+"""
+function param_sym_to_index end
+
+"""
+$(TYPEDSIGNATURES)
+
+Check if the given sym is a parameter variable in the given system.
+"""
+function is_param_sym end
+
+struct SymbolCache{S,T,U}
+    syms::S
+    indepsym::T
+    paramsyms::U
+end
+
+
+independent_variables(sc::SymbolCache) = sc.indepsym
+independent_variables(::SymbolCache{S,Nothing}) where {S} = []
+is_indep_sym(sc::SymbolCache, sym) = any(isequal(sym), sc.indepsym)
+is_indep_sym(::SymbolCache{S,Nothing}, _) where {S} = false
+states(sc::SymbolCache) = sc.syms
+states(::SymbolCache{Nothing}) = []
+state_sym_to_index(sc::SymbolCache, sym) = findfirst(isequal(sym), sc.syms)
+state_sym_to_index(::SymbolCache{Nothing}, _) = nothing
+is_state_sym(sc::SymbolCache, sym) = !isnothing(state_sym_to_index(sc, sym))
+parameters(sc::SymbolCache) = sc.paramsyms
+parameters(::SymbolCache{S,T,Nothing}) where {S,T} = []
+param_sym_to_index(sc::SymbolCache, sym) = findfirst(isequal(sym), sc.paramsyms)
+param_sym_to_index(::SymbolCache{S,T,Nothing}, _) where {S,T} = nothing
+is_param_sym(sc::SymbolCache, sym) = !isnothing(param_sym_to_index(sc, sym))
+  
+Base.copy(VA::SymbolCache) = typeof(VA)(
+    (VA.syms===nothing) ? nothing : copy(VA.syms),
+    (VA.indepsym===nothing) ? nothing : copy(VA.indepsym),
+    (VA.paramsyms===nothing) ? nothing : copy(VA.paramsyms),
+)
+

src/vector_of_array.jl

@@ -33,27 +33,6 @@ mutable struct VectorOfArray{T, N, A} <: AbstractVectorOfArray{T, N, A}
 end
 # VectorOfArray with an added series for time
 
-
-struct SymbolCache{S,T,U}
-  syms::S
-  indepsym::T
-  paramsyms::U
-end
-
-is_indep_sym(sc::SymbolCache, sym) = isequal(sc.indepsym, sym)
-is_indep_sym(::SymbolCache{S,Nothing}, _) where {S} = false
-state_sym_to_index(sc::SymbolCache, sym) = findfirst(isequal(sym), sc.syms)
-state_sym_to_index(::SymbolCache{Nothing}, _) = nothing
-is_state_sym(sc::SymbolCache, sym) = !isnothing(state_sym_to_index(sc, sym))
-param_sym_to_index(sc::SymbolCache, sym) = findfirst(isequal(sym), sc.paramsyms)
-param_sym_to_index(::SymbolCache{S,T,Nothing}, _) where {S,T} = nothing
-is_param_sym(sc::SymbolCache, sym) = !isnothing(param_sym_to_index(sc, sym))
-
-Base.copy(VA::SymbolCache) = typeof(VA)(
-    (VA.syms===nothing) ? nothing : copy(VA.syms),
-    (VA.indepsym===nothing) ? nothing : copy(VA.indepsym),
-    (VA.paramsyms===nothing) ? nothing : copy(VA.paramsyms),
-  )
 """
 ```julia
 DiffEqArray(u::AbstractVector,t::AbstractVector)