Merge pull request #3432 from AayushSabharwal/as/linearize-dependent-op

fix: fix symbolic maps given to `linearize`, warn in `linearization_function`

Author: ChrisRackauckas

src/linearization.jl

@@ -42,8 +42,12 @@ function linearization_function(sys::AbstractSystem, inputs,
         eval_expression = false, eval_module = @__MODULE__,
         warn_initialize_determined = true,
         guesses = Dict(),
+        warn_empty_op = true,
         kwargs...)
     op = Dict(op)
+    if isempty(op) && warn_empty_op
+        @warn "An empty operating point was passed to `linearization_function`. An operating point containing the variables that will be changed in `linearize` should be provided. Disable this warning by passing `warn_empty_op = false`."
+    end
     inputs isa AbstractVector || (inputs = [inputs])
     outputs isa AbstractVector || (outputs = [outputs])
     inputs = mapreduce(vcat, inputs; init = []) do var
@@ -590,9 +594,12 @@ function linearize(sys, lin_fun::LinearizationFunction; t = 0.0,
         p = DiffEqBase.NullParameters())
     prob = LinearizationProblem(lin_fun, t)
     op = anydict(op)
-    evaluate_varmap!(op, unknowns(sys))
+    evaluate_varmap!(op, keys(op))
     for (k, v) in op
         v === nothing && continue
+        if symbolic_type(v) != NotSymbolic() || is_array_of_symbolics(v)
+            v = getu(prob, v)(prob)
+        end
         if is_parameter(prob, Initial(k))
             setu(prob, Initial(k))(prob, v)
         else

test/downstream/linearize.jl

@@ -262,7 +262,7 @@ closed_loop = ODESystem(connections, t, systems = [model, pid, filt, sensor, r,
         filt.xd => 0.0
     ])
 
-@test_nowarn linearize(closed_loop, :r, :y)
+@test_nowarn linearize(closed_loop, :r, :y; warn_empty_op = false)
 
 # https://discourse.julialang.org/t/mtk-change-in-linearize/115760/3
 @mtkmodel Tank_noi begin
@@ -329,3 +329,19 @@ end
         sys, [x], []; op = Dict(x => 1.0), guesses = Dict(y => 1.0),
         allow_input_derivatives = true)
 end
+
+@testset "Symbolic values for parameters in `linearize`" begin
+    @named tank_noi = Tank_noi()
+    @unpack md_i, h, m, ρ, A, K = tank_noi
+    m_ss = 2.4000000003229878
+    @test_nowarn linearize(
+        tank_noi, [md_i], [h]; op = Dict(m => m_ss, md_i => 2, ρ => A / K, A => 5))
+end
+
+@testset "Warn on empty operating point" begin
+    @named tank_noi = Tank_noi()
+    @unpack md_i, h, m = tank_noi
+    m_ss = 2.4000000003229878
+    @test_warn ["empty operating point", "warn_empty_op"] linearize(
+        tank_noi, [md_i], [h]; p = [md_i => 1.0])
+end