[GiNaC-list] Given a formal iterated derivative (GiNaC::fderivative), what actually is it?

[Vladimir V. Kisil]

>>>>> On Sun, 10 Apr 2016 11:33:59 +0200, "Richard B. Kreckel" <kreckel at in.terlu.de> said:

    RK> On 04/10/2016 12:23 AM, Vladimir V. Kisil wrote:
    >>>>>>> On Sat, 9 Apr 2016 23:59:36 +0200, "Richard B. Kreckel"
    >>>>>>> <kreckel at in.terlu.de> said:
    >> >> f(x,y).diff(x, 3).diff(y, 2) >> which is printed as >>
    >> D[0,0,0,1,1](f)(x,y) >> This is fantastic.
    >> 
    RK> Hmmm...  Wouldn't it be more fantastic if it were printed
    RK> D[x,x,x,y,y](f)(x,y)?
    >> 
    >> But how to print f(x+y,x-y).diff(x, 3).diff(y, 2) in this case?

    RK> Well, I would have supposed like this:
    RK> D[x+y,x+y,x+y,x+y,x+y](f)(x+y,x-y)+D[x+y,x+y,x+y,x+y,x-y](f)(x+y,x-y)-2*D[x+y,x+y,x+y,x-y,x-y](f)(x+y,x-y)-2*D[x+y,x+y,x-y,x-y,x-y](f)(x+y,x-y)+D[x+y,x-y,x-y,x-y,x-y](f)(x+y,x-y)+D[x-y,x-y,x-y,x-y,x-y](f)(x+y,x-y)

    Yet, from a purist point of view, I have a concern that for
    f(x,x).diff(x, 3) the print-out will be ambiguous...
-- 
Vladimir V. Kisil                 http://www.maths.leeds.ac.uk/~kisilv/
  Book:     Geometry of Mobius Transformations     http://goo.gl/EaG2Vu
  Software: Geometry of cycles          http://moebinv.sourceforge.net/