Add substitute for ODEProblem

Author: YingboMa

src/systems/abstractsystem.jl

@@ -550,7 +550,7 @@ end
 
 flatten(sys::AbstractSystem, args...) = sys
 
-function equations(sys::ModelingToolkit.AbstractSystem)
+function equations(sys::AbstractSystem)
     eqs = get_eqs(sys)
     systems = get_systems(sys)
     if isempty(systems)
@@ -564,7 +564,7 @@ function equations(sys::ModelingToolkit.AbstractSystem)
     end
 end
 
-function preface(sys::ModelingToolkit.AbstractSystem)
+function preface(sys::AbstractSystem)
     has_preface(sys) || return nothing
     pre = get_preface(sys)
     systems = get_systems(sys)

src/systems/diffeqs/odesystem.jl

@@ -436,3 +436,9 @@ function convert_system(::Type{<:ODESystem}, sys, t; name = nameof(sys))
     return ODESystem(neweqs, t, newsts, parameters(sys); defaults = defs, name = name,
                      checks = false)
 end
+
+function Symbolics.substitute(sys::ODESystem, rules::Union{Vector{<:Pair}, Dict})
+    rules = todict(map(r->Symbolics.unwrap(r[1])=>Symbolics.unwrap(r[2]), collect(rules)))
+    eqs = fast_substitute(equations(sys), rules)
+    ODESystem(eqs, get_iv(sys); name = nameof(sys))
+end

test/odesystem.jl

@@ -12,6 +12,7 @@ using ModelingToolkit: value
 @constants κ = 1
 @variables x(t) y(t) z(t)
 D = Differential(t)
+@parameters k
 
 # Define a differential equation
 eqs = [D(x) ~ σ * (y - x),
@@ -20,6 +21,11 @@ eqs = [D(x) ~ σ * (y - x),
 
 ModelingToolkit.toexpr.(eqs)[1]
 @named de = ODESystem(eqs; defaults = Dict(x => 1))
+subed = substitute(de, [σ => k])
+@test isequal(sort(parameters(subed), by=string), [k, β, ρ])
+@test isequal(equations(subed), [D(x) ~ k*(y - x)
+                                 D(y) ~ (ρ - z)*x - y
+                                 D(z) ~ x*y - β*κ*z])
 @named des[1:3] = ODESystem(eqs)
 @test length(unique(x -> ModelingToolkit.get_tag(x), des)) == 1
 @test eval(toexpr(de)) == de