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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