Hi there!
I'm afraid that there is a slight bug in the InputForm of formal
derivatives in 1.3.5.
I guess the problem is that evaluation does not commute with
differentiation.
Best wishes,
Martin
(1) -> f := operator 'f
(1) f
Type:
BasicOperator
(2) -> unparse(eval(D(f(x,y), x, 1), x=y)::INFORM)
(2) "D(f(y,y),y::Symbol)"
Type:
String
(3) -> D(f(y,y),y::Symbol)
(3) f (y,y) + f (y,y)
,2 ,1
Type:
Expression(Integer)
or a bit more complicated:
(1) -> f := operator 'f
(1) f
Type:
BasicOperator
(2) -> ex := eval(D(f(x,y), [x, y], [1, 1]), x=x+y)
(2) f (y + x,y)
,1,2
Type:
Expression(Integer)
(3) -> iex := ex::INFORM
(3)
(D (eval (D (f %F y) (:: %F Symbol)) (:: %F Symbol) (+ y x)) (:: y
Symbol))
Type:
InputForm
(4) -> unparse(iex)
(4) "D(eval(D(f(%F,y),%F::Symbol),%F::Symbol,y+x),y::Symbol)"
Type:
String
(5) -> D(eval(D(f(%F,y),%F::Symbol),%F::Symbol,y+x),y::Symbol)
(5) f (y + x,y) + f (y + x,y)
,1,1 ,1,2
Type:
Expression(Integer)
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