Merge pull request #697 from SciML/myb/diff

Add special rules for max and min

Author: YingboMa

src/differentials.jl

@@ -197,7 +197,7 @@ derivative(f, args, v) = NoDeriv()
 # Pre-defined derivatives
 import DiffRules
 for (modu, fun, arity) ∈ DiffRules.diffrules()
-    fun in [:*, :+, :abs] && continue # special
+    fun in [:*, :+, :abs, :mod, :rem, :max, :min] && continue # special
     for i ∈ 1:arity
 
         expr = if arity == 1

src/extra_functions.jl

@@ -4,8 +4,23 @@
 
 @register Base.signbit(x)
 ModelingToolkit.derivative(::typeof(signbit), args::NTuple{1,Any}, ::Val{1}) = 0
-
 ModelingToolkit.derivative(::typeof(abs), args::NTuple{1,Any}, ::Val{1}) = IfElse.ifelse(signbit(args[1]),-one(args[1]),one(args[1]))
+function ModelingToolkit.derivative(::typeof(min), args::NTuple{2,Any}, ::Val{1})
+    x, y = args
+    IfElse.ifelse(x < y, one(x), zero(x))
+end
+function ModelingToolkit.derivative(::typeof(min), args::NTuple{2,Any}, ::Val{2})
+    x, y = args
+    IfElse.ifelse(x < y, zero(y), one(y))
+end
+function ModelingToolkit.derivative(::typeof(max), args::NTuple{2,Any}, ::Val{1})
+    x, y = args
+    IfElse.ifelse(x > y, one(x), zero(x))
+end
+function ModelingToolkit.derivative(::typeof(max), args::NTuple{2,Any}, ::Val{2})
+    x, y = args
+    IfElse.ifelse(x > y, zero(y), one(y))
+end
 
 @register IfElse.ifelse(x,y,z::Any)
 ModelingToolkit.derivative(::typeof(IfElse.ifelse), args::NTuple{3,Any}, ::Val{1}) = 0