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

Richard B. Kreckel kreckel at in.terlu.de
Sun Apr 10 11:33:59 CEST 2016

```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?

Well, I would have supposed like this:
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)

A trivial patch is attached.

All my best,
-richy.
--
Richard B. Kreckel
<http://in.terlu.de/~kreckel/>
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