test: add tests for if-lifting

Author: AayushSabharwal

test/if_lifting.jl

@@ -0,0 +1,110 @@
+using ModelingToolkit, OrdinaryDiffEq
+using ModelingToolkit: t_nounits as t, D_nounits as D, IfLifting, no_if_lift
+
+@testset "Simple `abs(x)`" begin
+    @mtkmodel SimpleAbs begin
+        @variables begin
+            x(t)
+            y(t)
+        end
+        @equations begin
+            D(x) ~ abs(y)
+            y ~ sin(t)
+        end
+    end
+    @named sys = SimpleAbs()
+    ss1 = structural_simplify(sys)
+    @test length(equations(ss1)) == 1
+    ss2 = structural_simplify(sys, additional_passes = [IfLifting])
+    @test length(equations(ss2)) == 1
+    @test length(parameters(ss2)) == 1
+    @test operation(only(equations(ss2)).rhs) === ifelse
+
+    discvar = only(parameters(ss2))
+    prob2 = ODEProblem(ss2, [x => 0.0], (0.0, 5.0))
+    sol2 = solve(prob2, Tsit5())
+    @test count(isapprox(pi), sol2.t) == 2
+    @test any(isapprox(pi), sol2.discretes[1].t)
+    @test !sol2[discvar][1]
+    @test sol2[discvar][end]
+
+    _t = pi + 1.0
+    # x(t) = 1 - cos(t) in [0, pi)
+    # x(t) = 3 + cos(t) in [pi, 2pi)
+    _trueval = 3 + cos(_t)
+    @test !isapprox(sol1(_t)[1], _trueval; rtol = 1e-3)
+    @test isapprox(sol2(_t)[1], _trueval; rtol = 1e-3)
+end
+
+@testset "Big test case" begin
+    @mtkmodel BigModel begin
+        @variables begin
+            x(t)
+            y(t)
+            z(t)
+            c(t)::Bool
+            w(t)
+            q(t)
+            r(t)
+        end
+        @parameters begin
+            p
+        end
+        @equations begin
+            # ifelse, max, min
+            D(x) ~ ifelse(c, max(x, y), min(x, y))
+            # discrete observed
+            c ~ x <= y
+            # observed should also get if-lifting
+            y ~ abs(sin(t))
+            # should be ignored
+            D(z) ~ no_if_lift(ifelse(x < y, x, y))
+            # ignore time-independent ifelse
+            D(w) ~ ifelse(p < 3, 1.0, 2.0)
+            # all the boolean operators
+            D(q) ~ ifelse((x < 1) & ((y < 0.5) | ifelse(y > 0.8, c, !c)), 1.0, 2.0)
+            # don't touch time-independent condition, but modify time-dependent branches
+            D(r) ~ ifelse(p < 2, abs(x), max(y, 0.9))
+        end
+    end
+
+    @named sys = BigModel()
+    ss = structural_simplify(sys, additional_passes = [IfLifting])
+
+    ps = parameters(ss)
+    @test length(ps) == 9
+    eqs = equations(ss)
+    obs = observed(ss)
+
+    @testset "no_if_lift is untouched" begin
+        idx = findfirst(eq -> isequal(eq.lhs, D(ss.z)), eqs)
+        eq = eqs[idx]
+        @test isequal(eq.rhs, no_if_lift(ifelse(ss.x < ss.y, ss.x, ss.y)))
+    end
+    @testset "time-independent ifelse is untouched" begin
+        idx = findfirst(eq -> isequal(eq.lhs, D(ss.w)), eqs)
+        eq = eqs[idx]
+        @test operation(arguments(eq.rhs)[1]) === Base.:<
+    end
+    @testset "time-dependent branch of time-independent condition is modified" begin
+        idx = findfirst(eq -> isequal(eq.lhs, D(ss.r)), eqs)
+        eq = eqs[idx]
+        @test operation(eq.rhs) === ifelse
+        args = arguments(eq.rhs)
+        @test operation(args[1]) == Base.:<
+        @test operation(args[2]) === ifelse
+        condvars = ModelingToolkit.vars(arguments(args[2])[1])
+        @test length(condvars) == 1 && any(isequal(only(condvars)), ps) 
+        @test operation(args[3]) === ifelse
+        condvars = ModelingToolkit.vars(arguments(args[3])[1])
+        @test length(condvars) == 1 && any(isequal(only(condvars)), ps) 
+    end
+    @testset "Observed variables are modified" begin
+        idx = findfirst(eq -> isequal(eq.lhs, ss.c), obs)
+        eq = obs[idx]
+        @test operation(eq.rhs) === Base.:! && any(isequal(only(arguments(eq.rhs))), ps)
+        idx = findfirst(eq -> isequal(eq.lhs, ss.y), obs)
+        eq = obs[idx]
+        @test operation(eq.rhs) === ifelse
+    end
+end

test/runtests.jl

@@ -83,6 +83,7 @@ end
             @safetestset "JumpSystem Test" include("jumpsystem.jl")
             @safetestset "print_tree" include("print_tree.jl")
             @safetestset "Constraints Test" include("constraints.jl")
+            @safetestset "IfLifting Test" include("if_lifting.jl")
         end
     end