Re: Series question: limiting total derivative order
- To: mathgroup at smc.vnet.net
- Subject: [mg95148] Re: Series question: limiting total derivative order
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Wed, 7 Jan 2009 07:11:37 -0500 (EST)
- Organization: Uni Leipzig
- References: <gk1rod$ouc$1@smc.vnet.net>
- Reply-to: kuska at informatik.uni-leipzig.de
Hi,
Normal[Series[f[x, y], {x, 0, 2}, {y, 0, 2}]] /.
Derivative[dlst__][f][args__] /; Plus[dlst] > 2 :> 0
Regards
Jens
carlos at colorado.edu wrote:
> Is it possible to directly tell Series to truncate a
> multivariate Taylor series beyond a total derivative order?
> Example, for f(x,y) and total derivative order 2, I want
>
> f(0,0) + x*Derivative[1,0][f][0,0] + y*Derivative[0,1][f][0,0] +
> x^2*Derivative[2,0][f][0,0]/2 + x*y*Derivative[1,1][f][0,0] +
> y^2*Derivative[0,2][f][0,0]/2
>
> whereas
>
> Normal[Series[f[x,y],{x,0,2},{y,0,2}]]
>
> returns also derivative terms (2,1), (1,2) and (2,2) of total
> orders 3, 3 and 4. These I have to get rid of a posteriori with
> some complicated logic to build a replacement list.
>