Re: Problems with Simplify

• To: mathgroup at smc.vnet.net
• Subject: [mg89325] Re: Problems with Simplify
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Thu, 5 Jun 2008 00:45:59 -0400 (EDT)
• References: <g25nsa\$htv\$1@smc.vnet.net>

```Hi,

I love it to extract Mathematica input from PDF documents.
It is total stupid to post Mathematica/ASCII input or
a notebook. This would allow to simply copy and paste
your input of the question. Too easy ...

X[u_, v_] := {(a + r Cos[u]) Cos[v], (a + r Cos[u]) Sin[v], r Sin[u]};
Xu = D[X[u, v], u];
Xv = D[X[u, v], v];
Xuu = D[X[u, v], {u, 2}];
Xuv = D[X[u, v], u, v];
Xvv = D[X[u, v], {v, 2}];

assume = Element[{a, r, u, v} , Reals] && a > 0 && r > 0 && a > r;

and

vec = FullSimplify[Cross[Xu, Xv], asssume];
nrm = FullSimplify[vec.vec, assume];
Nu = FullSimplify[vec/Sqrt[nrm], assume]

gives the desired result

as well as

FullSimplify[Nu.Xuu, assume]

Regards
Jens

Miguel wrote:
> How can I simplify complicated expressions with Simplify, FullSimplify
> or Refine. For example
>
> http://mathematicaes.googlegroups.com/web/Simplify.pdf?gsc=IgRnDgsAAAAdvdy0RPKGscv2nC8G3MUA
>
> Thanks
>

```

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