power series in more than one variables

*To*: mathgroup at smc.vnet.net*Subject*: [mg55679] power series in more than one variables*From*: "Christoph Lhotka" <lhotka at astro.univie.ac.at>*Date*: Sun, 3 Apr 2005 05:50:48 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Hello ! How can I define a power series in Mathematica with more than more variables (x,y,z,...), where only terms x^k*y^l*z^m*..., where k+l+m+...=N should be considered? I havwe tried Series[exp,{x,..},{y,...},...] but this only returns nested taylor series. My usual approach is to define an artificial perturbation parameter, say lambda^k+l+m, holding terms of equal powers together, but this is not satisfying when only dealing with numerical series, where the coefficients should only be numeric not mixed symbolic (defining it this way will give you as third argument to SeriesData non numerical entries. Does anyone have some sugestions? -- Christoph Lhotka -- University of Vienna Institute for Astronomy Tuerkenschanzstr. 17 1180 Vienna, Austria mail. lhotka at astro.univie.ac.at