Remove requirement that DVars have dependents

Author: HarrisonGrodin

src/variables.jl

@@ -11,11 +11,7 @@ Variable(name, args...; kwargs...) = Variable(name, args...; subtype=:Variable,
 
 Parameter(name,args...;kwargs...) = Variable(name,args...;subtype=:Parameter,kwargs...)
 IndependentVariable(name,args...;kwargs...) = Variable(name,args...;subtype=:IndependentVariable,kwargs...)
-
-function DependentVariable(name,args...;dependents = [],kwargs...)
-    @assert !isempty(dependents)
-    Variable(name,args...;subtype=:DependentVariable,dependents=dependents,kwargs...)
-end
+DependentVariable(name,args...;kwargs...) = Variable(name,args...;subtype=:DependentVariable,kwargs...)
 
 export Variable,Parameter,Constant,DependentVariable,IndependentVariable,
        @Var, @Param, @Const, @DVar, @IVar

test/basic_variables_and_operations.jl

@@ -3,7 +3,6 @@ using Test
 
 @IVar t
 @DVar x(t) y(t) z(t)
-@test_throws AssertionError @DVar w
 
 @Deriv D'~t # Default of first derivative, Derivative(t,1)
 @Param σ ρ β