chore: add change_tunables

src/parameters.jl

@@ -147,3 +147,27 @@ function split_parameters_by_type(ps)
         end
     end
 end
+
+"""
+    $(TYPEDSIGNATURES)
+
+Change the tunable parameters of a system to a new set of tunables.
+
+The new tunable parameters must be a subset of the current tunables as discovered by [`tunable_parameters`](@ref).
+The remaining parameters will be set as constants in the system.
+"""
+function change_tunables(sys, new_tunables)
+    cur_tunables = tunable_parameters(sys, parameters(sys))
+    diff_params = setdiff(cur_tunables, new_tunables)
+
+    if !isempty(setdiff(new_tunables, cur_tunables))
+        throw(ArgumentError("New tunables must be a subset of the current tunables. Found tunable parameters not in the system: $(setdiff(new_tunables, cur_tunables))"))
+    end
+    cur_ps = get_ps(sys)
+    const_ps = toconstant.(diff_params)
+
+    new_ps = replace(cur_ps, (diff_params .=> const_ps)...)
+    new_ps = replace(new_ps, (Initial.(diff_params) .=> Initial.(const_ps))...)
+    @set! sys.ps = new_ps
+    complete(sys)
+end

test/parameter_dependencies.jl

@@ -173,6 +173,24 @@ end
     @test SciMLBase.successful_retcode(sol)
 end
 
+@testset "Change Tunables" begin
+    @variables θ(t)=π/6 ω(t)=0.
+    @parameters g=9.81 L=1.0 b=0.1 errp=1
+    eqs = [
+        D(θ) ~ ω,
+        D(ω) ~ -(g/L)*sin(θ) - b*ω
+    ]
+    @named pendulum_sys = System(eqs, t, [θ, ω], [g, L, b])
+    sys = mtkcompile(pendulum_sys)
+
+    new_tunables = [L, b]
+    sys2 = ModelingToolkit.change_tunables(sys, new_tunables)
+    sys2_tunables = ModelingToolkit.tunable_parameters(sys2, ModelingToolkit.parameters(sys2))
+    @test length(sys2_tunables) == 2
+    @test isempty(setdiff(sys2_tunables, new_tunables))
+    @test_throws ArgumentError ModelingToolkit.change_tunables(sys, [errp])
+end
+
 struct CallableFoo
     p::Any
 end