MathGroup Archive: June 2008 [00153]

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Selecting Element from List via Pattern Matching

To: mathgroup at smc.vnet.net
Subject: [mg89396] Selecting Element from List via Pattern Matching
From: immanuel.bloch at googlemail.com
Date: Sun, 8 Jun 2008 02:32:39 -0400 (EDT)

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: Selecting Element from List via Pattern Matching
  - From: "Adriano Pascoletti" <adriano.pascoletti@gmail.com>
- Re: Selecting Element from List via Pattern Matching
  - From: Andrzej Kozlowski <akoz@mimuw.edu.pl>
- Re: Selecting Element from List via Pattern Matching
  - From: "W_Craig Carter" <ccarter@mit.edu>

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