RE: Expansion Coefficients in Multivariate Series Expansions?

*To*: mathgroup at smc.vnet.net*Subject*: [mg26607] RE: [mg26579] Expansion Coefficients in Multivariate Series Expansions?*From*: "David Park" <djmp at earthlink.net>*Date*: Thu, 11 Jan 2001 10:39:16 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

extractCoeff[term_][expr_] := Select[f, NumberQ[#/term] &]/term f = 50 + 2*x + 3*y + 4*z + 5*x*y + 6*x^2*y*z; (extractCoeff[#1][f] & ) /@ {1, x, y, z, x*y, x^2*y*z, x^3} {50, 2, 3, 4, 5, 6, 0} David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ > From: A. E. Siegman [mailto:siegman at stanford.edu] To: mathgroup at smc.vnet.net > > Given an expression that is the sum of products of integer powers of > three variables (say x,y,z) multiplied by numerical coefficients: > > f = c000 + c100 x + c010 y + c001 z + c110 x y + c211 x^2 y z + . . . > > where the cijk's are all real numbers, and f may or may not be in > Normal (or other) form, how do I find the coefficient of a particular > term, e.g. c100 for the x term (*not* c1000 + c110 y), or ckmn for the > x^k y^m z^n term? > > Neither Coefficient nor SeriesCoefficient seems to do this -- and the > SeriesCoefficient[expr, {n1,n2,n3,..}] syntax seems to be mentioned but > neither explained or illustrated in the on-line Help. > > Thanks, siegman at stanford.edu >