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. >