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

• To: mathgroup at smc.vnet.net
• Subject: [mg66851] Re: Beginner--getting rid of dot products with zero
• From: "ben" <benjamin.friedrich at gmail.com>
• Date: Thu, 1 Jun 2006 06:55:30 -0400 (EDT)
• References: <e5jsas\$e48\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Hi Smanky,

I only understood half of your question,

Why do you apply Total[]?
Are there vector quantities?

Usually, partial derivatives should be straigt-forward

f[x_,y_]:=x+y+\[Alpha]

D[f[x,y],\[Alpha]]

Bye
Ben

smanky at gmx.de schrieb:

> 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.
>
> &#8706;\_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]]

```

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