       Re: Almost symbolic computations (?)

• To: mathgroup at smc.vnet.net
• Subject: [mg90505] Re: [mg90466] Almost symbolic computations (?)
• From: DrMajorBob <drmajorbob at att.net>
• Date: Fri, 11 Jul 2008 02:03:25 -0400 (EDT)
• References: <24624830.1215688345875.JavaMail.root@m08>

```The tutorial at "VectorAnalysis/tutorial/VectorAnalysis" says, "The
initial default coordinate system is Cartesian, with coordinate variables
Xx, Yy, and Zz."

So you didn't use proper variables.

Curl[{a x, a y, a z}, Cartesian[x, y, z]]

{0, 0, 0}

should be a special case of

Curl[{f[x, y, z], g[x, y, z], h[x, y, z]}, Cartesian[x, y, z]]

{-(g^(0,0,1))[x,y,z]+(h^(0,1,0))[x,y,z],(f^(0,0,1))[x,y,z]-(h^(1,0,0))[x,y,z],-(f^(0,1,0))[x,y,z]+(g^(1,0,0))[x,y,z]}

A little visual inspection confirms it.

Bobby

On Thu, 10 Jul 2008 05:35:14 -0500, Barbara Da Vinci

> 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
>
>

--
DrMajorBob at longhorns.com

```

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