Merge pull request #355 from SciML/s/deriv_simplify

keep the same result, do just 1 simplification

Author: ChrisRackauckas

Project.toml

@@ -39,7 +39,7 @@ RecursiveArrayTools = "2.3"
 SafeTestsets = "0.0.1"
 SpecialFunctions = "0.7, 0.8, 0.9, 0.10"
 StaticArrays = "0.10, 0.11, 0.12"
-SymbolicUtils = "0.3"
+SymbolicUtils = "0.3.2"
 TreeViews = "0.3"
 UnPack = "0.1, 1.0"
 Unitful = "1.1"

src/differentials.jl

@@ -37,7 +37,7 @@ $(SIGNATURES)
 TODO
 """
 function expand_derivatives(O::Operation,simplify=true)
-    @. O.args = expand_derivatives(O.args,simplify)
+    @. O.args = expand_derivatives(O.args,false)
 
     if isa(O.op, Differential)
         (D, o) = (O.op, O.args[1])
@@ -48,7 +48,7 @@ function expand_derivatives(O::Operation,simplify=true)
         isa(o.op, Variable) && return O
 
         x = sum(1:length(o.args)) do i
-            derivative(o, i) * expand_derivatives(D(o.args[i]),simplify)
+            derivative(o, i) * expand_derivatives(D(o.args[i]),false)
         end
 
         return simplify ? ModelingToolkit.simplify(x) : x