test: test parameters as initialization unknowns

Author: AayushSabharwal

test/initializationsystem.jl

@@ -486,3 +486,61 @@ sys = extend(sysx, sysy)
     ssys = structural_simplify(sys)
     @test_throws ArgumentError ODEProblem(ssys, [x => 3], (0, 1), []) # y should have a guess
 end
+
+@testset "Initialization of parameters" begin
+    function test_parameter(prob, sym, val, initialval = zero(val))
+        @test prob.ps[sym] ≈ initialval
+        @test init(prob, Tsit5()).ps[sym] ≈ val
+        @test solve(prob, Tsit5()).ps[sym] ≈ val
+    end
+    @variables x(t) y(t)
+    @parameters p
+    _p = ModelingToolkit.setdefault(p, missing)
+    _p = ModelingToolkit.setguess(_p, 0.0)
+    @mtkbuild sys = ODESystem([D(x) ~ x, _p ~ x + y], t)
+    prob = ODEProblem(sys, [x => 1.0, y => 1.0], (0.0, 1.0))
+    test_parameter(prob, _p, 2.0)
+    @mtkbuild sys = ODESystem(
+        [D(x) ~ x, p ~ x + y], t; defaults = [p => missing], guesses = [p => 0.0])
+    prob = ODEProblem(sys, [x => 1.0, y => 1.0], (0.0, 1.0))
+    test_parameter(prob, p, 2.0)
+    @mtkbuild sys = ODESystem([D(x) ~ x, p ~ x + y], t; guesses = [p => 0.0])
+    prob = ODEProblem(sys, [x => 1.0, y => 1.0], (0.0, 1.0), [p => missing])
+    test_parameter(prob, p, 2.0)
+
+    @mtkbuild sys = ODESystem([D(x) ~ x, p ~ x + y], t; guesses = [p => 1.0])
+    @test_throws ModelingToolkit.MissingParametersError ODEProblem(
+        sys, [x => 1.0, y => 1.0], (0.0, 1.0))
+    @mtkbuild sys = ODESystem([D(x) ~ x, p ~ x + y], t)
+    @test_throws ["Invalid setup", "parameter p", "guess"] ODEProblem(
+        sys, [x => 1.0, y => 1.0], (0.0, 1.0), [p => missing])
+
+    @testset "Null system" begin
+        @variables x(t) y(t) s(t)
+        @parameters x0 y0
+        @mtkbuild sys = ODESystem([x ~ x0, y ~ y0, s ~ x + y], t; guesses = [y0 => 0.0])
+        prob = ODEProblem(sys, [s => 1.0], (0.0, 1.0), [x0 => 0.3, y0 => missing])
+        test_parameter(prob, y0, 0.7)
+    end
+
+    using ModelingToolkitStandardLibrary.Mechanical.TranslationalModelica: Fixed, Mass,
+                                                                           Spring, Force,
+                                                                           Damper
+    using ModelingToolkitStandardLibrary.Blocks: Constant
+
+    @named mass = Mass(; m = 1.0, s = 1.0, v = 0.0, a = 0.0)
+    @named fixed = Fixed(; s0 = 0.0)
+    @named spring = Spring(; c = 2.0)
+    @named gravity = Force()
+    @named constant = Constant(; k = 9.81)
+    @named damper = Damper(; d = 0.1)
+    @mtkbuild sys = ODESystem(
+        [connect(fixed.flange, spring.flange_a), connect(spring.flange_b, mass.flange_a),
+            connect(mass.flange_a, gravity.flange), connect(constant.output, gravity.f),
+            connect(fixed.flange, damper.flange_a), connect(damper.flange_b, mass.flange_a)],
+        t;
+        systems = [fixed, spring, mass, gravity, constant, damper],
+        guesses = [spring.s_rel0 => 1.0])
+    prob = ODEProblem(sys, [], (0.0, 1.0), [spring.s_rel0 => missing])
+    test_parameter(prob, spring.s_rel0, -3.905)
+end