Re: Selecting Element from List via Pattern Matching

*To*: mathgroup at smc.vnet.net*Subject*: [mg89414] Re: [mg89396] Selecting Element from List via Pattern Matching*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Mon, 9 Jun 2008 02:26:50 -0400 (EDT)*Reply-to*: hanlonr at cox.net

t = List @@ Expand[(Sum[Subscript[a, i], {i, 1, 5}])^3]; Your expression works for the case given Cases[t, Times[_, Power[Subscript[a, 2], 2]]] {3*Subscript[a, 1]*Subscript[a, 2]^ 2, 3*Subscript[a, 2]^2* Subscript[a, 3], 3*Subscript[a, 2]^2*Subscript[a, 4], 3*Subscript[a, 2]^2* Subscript[a, 5]} However, it will not find power terms without another factor such as Cases[t, Times[_, Power[Subscript[a, 1], 3]]] {} Add a default Cases[t, Times[_., Power[Subscript[a, 1], 3]]] {Subscript[a, 1]^3} Bob Hanlon ---- immanuel.bloch at googlemail.com wrote: > Hello, > > I am trying to extract from a Power Series all elements with a > certain exponent, e.g. > let us say I have generated a list via > > t = Apply[List, Expand[(Sum[Subscript[a, i], {i, 1, 5}])^3]] > > How can I then extract all terms with e.g. a_2^2 in it or any other > exponent? > > I have tried something like > > Cases[t, Times[_, Power[Subscript[a,2],2]]] > > but this somehow only works with the exponent n=1 and no others... > > Does anybody know a solution to this pattern matching problem? > > Thanks! > Immanuel >

**Follow-Ups**:**Re: Re: Selecting Element from List via Pattern***From:*Syd Geraghty <sydgeraghty@mac.com>