remove robust flag

Author: Karl Wessel

src/diff.jl

@@ -150,8 +150,25 @@ function recursive_hasoperator(op, O)
     end
 end
 
-function executediff(D, arg, simplify=false; robust=false, occurrences=nothing)
-    if robust || occurrences == nothing
+"""
+    executediff(D, arg, simplify=false; occurrences=nothing)
+
+Apply the passed Differential D on the passed argument.
+
+This function differs to `expand_derivatives` in that in only expands the
+passed differential and not any other Differentials it encounters.
+
+# Arguments
+- `D::Differential`: The differential to apply
+- `arg::Symbolic`: The symbolic expression to apply the differential on.
+- `simplify::Bool=false`: Whether to simplify the resulting expression using
+    [`SymbolicUtils.simplify`](@ref).
+- `occurrences=nothing`: Information about the occurrences of the independent
+    variable in the argument of the derivative. This is used internally for
+    optimization purposes.
+"""
+function executediff(D, arg, simplify=false; occurrences=nothing)
+    if occurrences == nothing
         occurrences = occursin_info(D.x, arg)
     end
 
@@ -166,15 +183,15 @@ function executediff(D, arg, simplify=false; robust=false, occurrences=nothing)
             return D(arg) # base case if any argument is directly equal to the i.v.
         else
             return sum(inner_args, init=0) do a
-                return executediff(Differential(a), arg; robust) *
-                executediff(D, a; robust)
+                return executediff(Differential(a), arg) *
+                executediff(D, a)
             end
         end
     elseif op === (IfElse.ifelse)
         args = arguments(arg)
         O = op(args[1], 
-            executediff(D, args[2], simplify; robust, occurrences=arguments(occurrences)[2]), 
-            executediff(D, args[3], simplify; robust, occurrences=arguments(occurrences)[3]))
+            executediff(D, args[2], simplify; occurrences=arguments(occurrences)[2]), 
+            executediff(D, args[3], simplify; occurrences=arguments(occurrences)[3]))
         return O
     elseif isa(op, Differential)
         # The recursive expand_derivatives was not able to remove
@@ -184,20 +201,21 @@ function executediff(D, arg, simplify=false; robust=false, occurrences=nothing)
         if isequal(op.x, D.x)
             return D(arg)
         else
-            inner = executediff(D, arguments(arg)[1], false; robust)
+            inner = executediff(D, arguments(arg)[1], false)
             # if the inner expression is not expandable either, return
             if iscall(inner) && operation(inner) isa Differential
                 return D(arg)
             else
-                return expand_derivatives(op(inner), simplify; robust) # TODO
+                # otherwise give the nested Differential another try
+                return executediff(op, inner, simplify)
             end
         end
     elseif isa(op, Integral)
         if isa(op.domain.domain, AbstractInterval)
             domain = op.domain.domain
             a, b = DomainSets.endpoints(domain)
             c = 0
-            inner_function = expand_derivatives(arguments(arg)[1]; robust) # TODO
+            inner_function = arguments(arg)[1]
             if iscall(value(a))
                 t1 = SymbolicUtils.substitute(inner_function, Dict(op.domain.variables => value(a)))
                 t2 = D(a)
@@ -208,7 +226,7 @@ function executediff(D, arg, simplify=false; robust=false, occurrences=nothing)
                 t2 = D(b)
                 c += t1*t2
             end
-            inner = executediff(D, arguments(arg)[1]; robust)
+            inner = executediff(D, arguments(arg)[1])
             c += op(inner)
             return value(c)
         end
@@ -220,7 +238,7 @@ function executediff(D, arg, simplify=false; robust=false, occurrences=nothing)
     c = 0
 
     for i in 1:l
-        t2 = executediff(D, inner_args[i],false; robust, occurrences=arguments(occurrences)[i])
+        t2 = executediff(D, inner_args[i],false; occurrences=arguments(occurrences)[i])
 
         x = if _iszero(t2)
             t2
@@ -265,9 +283,6 @@ and other derivative rules to expand any derivatives it encounters.
 - `O::Symbolic`: The symbolic expression to expand.
 - `simplify::Bool=false`: Whether to simplify the resulting expression using
     [`SymbolicUtils.simplify`](@ref).
-- `occurrences=nothing`: Information about the occurrences of the independent
-    variable in the argument of the derivative. This is used internally for
-    optimization purposes.
 
 # Examples
 ```jldoctest
@@ -283,30 +298,29 @@ julia> dfx=expand_derivatives(Dx(f))
 (k*((2abs(x - y)) / y - 2z)*IfElse.ifelse(signbit(x - y), -1, 1)) / y
 ```
 """
-function expand_derivatives(O::Symbolic, simplify=false; robust=false, occurrences=nothing)
+function expand_derivatives(O::Symbolic, simplify=false)
     if iscall(O) && isa(operation(O), Differential)
         arg = only(arguments(O))
-        arg = expand_derivatives(arg, false; robust)
+        arg = expand_derivatives(arg, false)
+        return executediff(operation(O), arg, simplify)
     elseif iscall(O) && isa(operation(O), Integral)
-        return operation(O)(expand_derivatives(arguments(O)[1]; robust))
+        return operation(O)(expand_derivatives(arguments(O)[1]))
     elseif !hasderiv(O)
         return O
     else
-        args = map(a->expand_derivatives(a, false; robust), arguments(O))
+        args = map(a->expand_derivatives(a, false), arguments(O))
         O1 = operation(O)(args...)
         return simplify ? SymbolicUtils.simplify(O1) : O1
     end
-
-    executediff(operation(O), arg, simplify; robust, occurrences)
 end
-function expand_derivatives(n::Num, simplify=false; robust=false, occurrences=nothing)
-    wrap(expand_derivatives(value(n), simplify; robust, occurrences))
+function expand_derivatives(n::Num, simplify=false)
+    wrap(expand_derivatives(value(n), simplify))
 end
-function expand_derivatives(n::Complex{Num}, simplify=false; robust=false, occurrences=nothing)
-    wrap(ComplexTerm{Real}(expand_derivatives(real(n), simplify; robust, occurrences),
-                           expand_derivatives(imag(n), simplify; robust, occurrences)))
+function expand_derivatives(n::Complex{Num}, simplify=false)
+    wrap(ComplexTerm{Real}(expand_derivatives(real(n), simplify),
+                           expand_derivatives(imag(n), simplify)))
 end
-expand_derivatives(x, simplify=false; robust=false, occurrences=nothing) = x
+expand_derivatives(x, simplify=false) = x
 
 _iszero(x) = false
 _isone(x) = false

test/diff.jl

@@ -356,9 +356,8 @@ let
 	D = Differential(t)
 	expr = b - ((D(b))^2) * D(D(b))
 	expr2 = D(expr)
-	@test isequal(expand_derivatives(expr), expand_derivatives(expr; robust=true))
-    @test isequal(expand_derivatives(expr2; robust=true), D(b) - (D(b)^2)*D(D(D(b))) - 2D(b)*(D(D(b))^2))
-	@test isequal(expand_derivatives(expr2; robust=true), expand_derivatives(expr2))   
+	@test isequal(expand_derivatives(expr), expr)
+    @test isequal(expand_derivatives(expr2), D(b) - (D(b)^2)*D(D(D(b))) - 2D(b)*(D(D(b))^2))
 end
 
 # 1126
@@ -370,13 +369,13 @@ let
     expr_gen = (fun) -> D(D(((-D(D(fun))) / g(y))))
 
     expr = expr_gen(g(y))
-    @test isequal(expand_derivatives(expr), expand_derivatives(expr; robust=true))
+    # just make sure that no errors are thrown in the following, the results are to complicated to compare
+    expand_derivatives(expr)
     expr = expr_gen(h(y))
-    @test isequal(expand_derivatives(expr), expand_derivatives(expr; robust=true))
+    expand_derivatives(expr)
 
-    expected = substitute(expand_derivatives(expr; robust=true), h(y) => f(y))
     expr = expr_gen(f(y))
-    @test isequal(expand(expand_derivatives(expr)), expand(expand_derivatives(expr; robust=true)))
+    expand_derivatives(expr)
 end
 
 # Check `is_derivative` function