Hi Martin
I suppose this problem is even more involved:

f:=operator 'f
g(x,y) == D(f(x,y), x)
G(x,y) == eval(D(f(t,s), t),[t=x,s=y])

expr:=D(f(x,y), x, 1)
function(expr, h, [x,y])

Then G(q,q) is what I had expected, but neither g nor h may be considered 
as functions. 
The problem seems to be that we here deal with a kind of "macro", i.e. 
G,g,h are not functions as long as 'f' is not concrete.

Even unparse(G(q,q)::INFORM) yields "D(f(q,q),q::Symbol)" :(

I guess this requires some fundamental changes?

Best
Kurt



(8) -> [G(x,x),g(x,x),h(x,x)]
   Compiling function g with type (Variable(x), Variable(x)) -> 
      Expression(Integer) 
   Compiling function h with type (Variable(x), Variable(x)) -> 
      Expression(Integer) 

   (8)  [f  (x,x), f  (x,x) + f  (x,x), f  (x,x) + f  (x,x)]
          ,1        ,2         ,1        ,2         ,1
                                              Type: 
List(Expression(Integer))


On Saturday, 16 February 2019 23:41:35 UTC+1, Martin R wrote:
>
> 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
>
>
>
>

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