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MathGroup Archive 2006

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Beginner--getting rid of dot products with zero

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66818] Beginner--getting rid of dot products with zero
  • From: smanky at gmx.de
  • Date: Wed, 31 May 2006 06:31:27 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

hello,

i am economics student... not very familiar with mathematica yet.

i am currently using mathematica to verify derivatives i need in another system's code. and, i am stuck with a not so uncommon problem. however, browsing forums i haven't found the solution for my particular version of the problem yet.

when taking partial derivatives of this expression:

L[k1_, k2_, alpha_, beta_ ] = Total[Log[q[k1, k2]]] + Total[(y - alpha - beta*q[k1, k2])^2/q[k1, k2]];

e.g. 

∂\_alpha\ L[k1, \ k2, \ alpha, \ beta]

the results include terms like e.g. 

x.{0,0,0} or 0.{, ,}

how can i get rid of those? one way is probably by using a replace rule, but this seems rather cumbersome, beside the mere fact that i didn't even get this to work, yet. Simplify, or FullSimplify don't help either.

any suggestions are greatly appreciated.

cheers,

~stephan

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http://www.mathematica-users.org/webMathematica/wiki/wiki.jsp?pageName=Special:Forum_ViewTopic&pid=10721#p10721
Posted through http://www.mathematica-users.org [[postId=10721]]



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