Forbid DDEs for now

Author: hersle

src/systems/diffeqs/basic_transformations.jl

@@ -105,6 +105,8 @@ function change_independent_variable(sys::AbstractODESystem, iv, eqs = []; dummi
 
     if !iscomplete(sys)
         error("System $(nameof(sys)) is incomplete. Complete it first!")
+    elseif is_dde(sys)
+        error("System $(nameof(sys)) contains delay differential equations (DDEs). This is currently not supported!")
     elseif isscheduled(sys)
         error("System $(nameof(sys)) is structurally simplified. Change independent variable before structural simplification!")
     elseif !iscall(iv2_of_iv1) || !isequal(only(arguments(iv2_of_iv1)), iv1)

test/basic_transformations.jl

@@ -152,4 +152,8 @@ end
     @test_throws "not specified" change_independent_variable(M, v)
     @test_throws "not a function of the independent variable" change_independent_variable(M, y)
     @test_throws "not a function of the independent variable" change_independent_variable(M, z)
+    M = ODESystem([D(x) ~ 0, v ~ x], t; name = :M)
+    @variables x(..) # require explicit argument
+    M = ODESystem([D(x(t)) ~ x(t-1)], t; name = :M) |> complete
+    @test_throws "DDE" change_independent_variable(M, M.x)
 end