Re: Beginner--getting rid of dot products with zero

*To*: mathgroup at smc.vnet.net*Subject*: [mg66849] Re: Beginner--getting rid of dot products with zero*From*: "Arkadiusz Majka" <Arkadiusz.Majka at telekomunikacja.pl>*Date*: Thu, 1 Jun 2006 06:55:20 -0400 (EDT)*References*: <e5jsas$e48$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hmmm, here there is everything ok.... :) In[547]:= L[k1_, k2_, alpha_, beta_ ] = Total[Log[ q[k1, k2]]] + Total[(y - alpha - beta*q[k1, k2])^2/q[k1, k2]] Out[547]= \!\(1\/q[k1, k2] + q[k1, k2] + \((\(-alpha\) + y - beta\ q[k1, k2])\)\^2\) In[548]:= D[L[k1,k2,alpha,beta],alpha] Out[548]= -2 (-alpha+y-beta q[k1,k2]) smanky at gmx.de napisal(a): > 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 > > Link to the forum page for this post: > 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]]