feat: add default t and D

Author: AayushSabharwal

examples/electrical_components.jl

@@ -1,7 +1,7 @@
 using Test
 using ModelingToolkit, OrdinaryDiffEq
+using ModelingToolkit: t_nounits as t, D_nounits as D
 
-@isdefined(t) || @parameters t
 @connector function Pin(; name)
     sts = @variables v(t)=1.0 i(t)=1.0 [connect = Flow]
     ODESystem(Equation[], t, sts, []; name = name)
@@ -37,7 +37,6 @@ end
     @named oneport = OnePort()
     @unpack v, i = oneport
     ps = @parameters C = C
-    D = Differential(t)
     eqs = [
         D(v) ~ i / C,
     ]
@@ -58,7 +57,6 @@ end
     @named oneport = OnePort()
     @unpack v, i = oneport
     ps = @parameters L = L
-    D = Differential(t)
     eqs = [
         D(i) ~ v / L,
     ]
@@ -89,7 +87,6 @@ end
     @parameters rho=rho V=V cp=cp
     C = rho * V * cp
     @named h = HeatPort()
-    D = Differential(t)
     eqs = [
         D(h.T) ~ h.Q_flow / C,
     ]

src/ModelingToolkit.jl

@@ -74,6 +74,9 @@ end
 @reexport using UnPack
 RuntimeGeneratedFunctions.init(@__MODULE__)
 
+import DynamicQuantities, Unitful
+const DQ = DynamicQuantities
+
 export @derivatives
 
 for fun in [:toexpr]
@@ -172,11 +175,24 @@ for S in subtypes(ModelingToolkit.AbstractSystem)
     @eval convert_system(::Type{<:$S}, sys::$S) = sys
 end
 
+const t_nounits = let
+    only(@parameters t)
+end
+const t_unitful = let
+    only(@parameters t [unit = Unitful.u"s"])
+end
+const t = let
+    only(@parameters t [unit = DQ.u"s"])
+end
+
+const D_nounits = Differential(t_nounits)
+const D_unitful = Differential(t_unitful)
+const D = Differential(t)
+
 PrecompileTools.@compile_workload begin
     using ModelingToolkit
-    @variables t x(t)
-    D = Differential(t)
-    @named sys = ODESystem([D(x) ~ -x])
+    @variables x(ModelingToolkit.t_nounits)
+    @named sys = ODESystem([ModelingToolkit.D_nounits(x) ~ -x])
     prob = ODEProblem(structural_simplify(sys), [x => 30.0], (0, 100), [], jac = true)
 end
 

src/systems/unit_check.jl

@@ -1,6 +1,3 @@
-import DynamicQuantities, Unitful
-const DQ = DynamicQuantities
-
 #For dispatching get_unit
 const Conditional = Union{typeof(ifelse), typeof(IfElse.ifelse)}
 const Comparison = Union{typeof.([==, !=, ≠, <, <=, ≤, >, >=, ≥])...}

test/extensions/bifurcationkit.jl

@@ -1,10 +1,10 @@
 using BifurcationKit, ModelingToolkit, Test
-
+using ModelingToolkit: t_nounits as t, D_nounits as D
 # Simple pitchfork diagram, compares solution to native BifurcationKit, checks they are identical.
 # Checks using `jac=false` option.
 let
     # Creates model.
-    @variables t x(t) y(t)
+    @variables x(t) y(t)
     @parameters μ α
     eqs = [0 ~ μ * x - x^3 + α * y,
         0 ~ -y]
@@ -57,8 +57,7 @@ end
 let
     # Creates a Lotka–Volterra model.
     @parameters α a b
-    @variables t x(t) y(t) z(t)
-    D = Differential(t)
+    @variables x(t) y(t) z(t)
     eqs = [D(x) ~ -x + a * y + x^2 * y,
         D(y) ~ b - a * y - x^2 * y]
     @named sys = ODESystem(eqs)
@@ -99,8 +98,7 @@ end
 let
     # Creates model, and uses `structural_simplify` to generate observables.
     @parameters μ p=2
-    @variables t x(t) y(t) z(t)
-    D = Differential(t)
+    @variables x(t) y(t) z(t)
     eqs = [0 ~ μ - x^3 + 2x^2,
         0 ~ p * μ - y,
         0 ~ y - z]