Fix vars

Author: YingboMa

src/systems/diffeqs/odesystem.jl

@@ -86,11 +86,12 @@ iv_from_nested_derivative(x::Term) = operation(x) isa Differential ? iv_from_nes
 iv_from_nested_derivative(x::Sym) = x
 iv_from_nested_derivative(x) = missing
 
-vars(exprs::Term) = vars([exprs])
+vars(x::Sym) = [x]
+vars(exprs::Symbolic) = vars([exprs])
 vars(exprs) = foldl(vars!, exprs; init = Set())
 function vars!(vars, O)
     isa(O, Sym) && return push!(vars, O)
-    !isa(O, Term) && return vars
+    !isa(O, Symbolic) && return vars
 
     operation(O) isa Sym && push!(vars, O)
     for arg ∈ arguments(O)

test/direct.jl

@@ -13,9 +13,9 @@ eqs = [σ*(y-x),
        x*y - β*z]
 
 
-simpexpr = Expr[:($(*)(σ, $(-)(y, x))),
-                :($(-)($(*)(x, $(-)(ρ, z)), y)),
-                :($(-)($(*)(x, y), $(*)(β, z)))]
+simpexpr = Expr[:($(*)(σ, $(+)($(*)(-1, x), y))),
+                :($(+)($(*)(x, $(+)($(*)(-1, z), ρ)), $(*)(-1, y))),
+                :($(+)($(*)(x, y), $(*)(-1, z, β)))]
 
 for i in 1:3
    @test ModelingToolkit.toexpr.(eqs)[i] == simpexpr[i]