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MathGroup Archive 2006

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

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66882] RE:Beginner--getting rid of dot products with zero
  • From: smanky at gmx.de
  • Date: Fri, 2 Jun 2006 04:09:25 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

sorry that my question was apparently not clear.

i have no problem with computing the derivatives. the expressions with Total[] etc all make sense. 

however, the derivatives include ugly terms that are simply zero. there are terms of the following form

0.{exp, exp, exp}

or 

{exp, exp, exp}.0

in both cases the whole thing is zero and they should drop out...

i am surprised that mathematica is not getting rid of them by itself, or at least when i use Simplify[]. so i am looking for a clever way to tell mathematica that it should disregard those terms.

thanks,

~s

p.s. if it is still not clear, or you just want to see for yourself, run:

finish = 2;
i = Table[i, {i, finish}];

d1[k1_, k2_] = Exp[k1*i + k2*i^2];
d2[k1_, k2_] = Total[Exp[k1*i + k2*i^2]];

w[k1_, k2_, i] = d1[k1, k2]/d2[k1, k2];

q[k1_, k2_] = x.w[k1, k2, i];


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

\!\(Simplify[∂\_beta\ L[k1, \ k2, \ alpha, \ beta]]\)   

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