Add n-ary *, + rules

Author: YingboMa

Project.toml

@@ -1,7 +1,7 @@
 name = "ModelingToolkit"
 uuid = "961ee093-0014-501f-94e3-6117800e7a78"
 authors = ["Chris Rackauckas <accounts@chrisrackauckas.com>"]
-version = "1.2.2"
+version = "1.2.3"
 
 [deps]
 DiffEqBase = "2b5f629d-d688-5b77-993f-72d75c75574e"

src/differentials.jl

@@ -109,9 +109,8 @@ for (modu, fun, arity) ∈ DiffRules.diffrules()
     end
 end
 
-derivative(::typeof(+), args::NTuple{T,Operation}, ::Val{i}) where {T,i} = args[i]
-derivative(::typeof(+), args::Tuple{Operation,Operation}, ::Val{1}) = args[1]
-derivative(::typeof(+), args::Tuple{Operation,Operation}, ::Val{2}) = args[2]
+derivative(::typeof(+), args::NTuple{N,Operation}, ::Val) where {N} = 1
+derivative(::typeof(*), args::NTuple{N,Operation}, ::Val{i}) where {N,i} = Operation(*, deleteat!(collect(args), i))
 
 function count_order(x)
     @assert !(x isa Symbol) "The variable $x must have an order of differentiation that is greater or equal to 1!"

test/derivatives.jl

@@ -60,3 +60,7 @@ jac = calculate_jacobian(sys)
 @test isequal(expand_derivatives(D(2t)), 2)
 @test isequal(expand_derivatives(D(2x)), 2D(x))
 @test isequal(expand_derivatives(D(x^2)), simplify_constants(2 * x * D(x)))
+
+# n-ary * and +
+isequal(ModelingToolkit.derivative(Operation(*, [x, y, z*ρ]), 1), y*(z*ρ))
+isequal(ModelingToolkit.derivative(Operation(+, [x*y, y, z]), 1), 1)