Re: Almost symbolic computations (?)

• To: mathgroup at smc.vnet.net
• Subject: [mg90485] Re: Almost symbolic computations (?)
• From: Peter Breitfeld <phbrf at t-online.de>
• Date: Thu, 10 Jul 2008 07:07:06 -0400 (EDT)
• References: <g54oim\$etu\$1@smc.vnet.net>

```Barbara Da Vinci schrieb:
> Dear MathGroup
>
> This is an example of the problem
> I'm facing.
>
> The code
>
>    Needs["VectorAnalysis`"];
>    Head /@ {ax, ay, az}
>    A = {ax, ay, az};
>      Curl[A]
>
> returns
>
> {Symbol, Symbol, Symbol}
> {0, 0, 0}
>
> Instead, I would get the
> well known symbolic form
>
> d_y az - d_z ay
> ...
>
> I have been trying, for
> a while, to perform string
> manipulations but that,
> of course, lays to ashes
> the possibility to recognize
>
> d_y az + d_y az = 2 d_y az
>
> and so on.
>
> Any way to get out of it ?
>
> Kind regards
>
>
> Barbara Da Vinci
>

Barbara,

your variables don't depend on anything, so Mathematica treats them
as constants, therefore the derivatives are 0.

Try this:

X = Sequence[x, y, z];
SetCoordinates[Cartesian[x, y, z]];
A = {ax[X], ay[X], az[X]};
Curl[A]

Gruss Peter
--
==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==
Peter Breitfeld, Bad Saulgau, Germany -- http://www.pBreitfeld.de

```

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