Re: Re: Derivative of a funtion evaluated at a point in 3D

• To: mathgroup at smc.vnet.net
• Subject: [mg44473] Re: [mg44468] Re: Derivative of a funtion evaluated at a point in 3D
• From: christopherpurcell <christopherpurcell at mac.com>
• Date: Wed, 12 Nov 2003 08:01:24 -0500 (EST)
• References: <boign7\$oj1\$1@smc.vnet.net> <200311110055.TAA25212@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```The question is ill-posed - you have not provided a complete enough
description
there is no way to know.
If in fact you really want to evaluate D[F,p1,p2,p3,p4] then the answer
could well be 0 (p1,p2,p3,p4 were most likely taken to be scalars not
vectors by D).
Consider this trivial example:
F = ({x1, x2, x3} + {y1, y2, y3} + {z1, z2, z3})/3;
D[F, x1, x2, x3] (* mixed partials vanish *)
I suspect what you want is something more like:
{{D[F, x1], D[F, x2], D[F, x3]},{D[F, y1], D[F, y2], D[F, y3]},{D[F,
z1], D[F, z2], D[F, z3]}}
You should evaluate ?D and follow the links to the help browser entries
for D to see what this expression (D[F,p1,p2,p3,p4] ) means.

On Nov 10, 2003, at 8:55 PM, mroc wrote:

> mroc_1000 at hotmail.com (mroc) wrote in message
> news:<boign7\$oj1\$1 at smc.vnet.net>...
>> Hello, I am totally new to Mathematica and trying to program a simple
>> FEM-type problem. I am trying to take the partial derivative
>> (symbolically) of an expression that is a function of four points in
>> 3D. All I can think of to do is F[p1,p2,p3,p4] = stuff then
>> D[F,p1,p2,p3,p4] . But I keep getting a zero expression as a result.
>> (where stuff is a nasty combination of these points) Any thoughts?
>
> Anyone? What am I missing? Is this question too easy or too hard?
>
>
Dr Christopher Purcell
Sensors & Actuators Group
DRDC-Atlantic, 9 Grove St., PO Box 1012,