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

• To: mathgroup at smc.vnet.net
• Subject: [mg44502] Re: Derivative of a funtion evaluated at a point in 3D
• Date: Wed, 12 Nov 2003 08:02:06 -0500 (EST)
• References: <boign7\$oj1\$1@smc.vnet.net> <bopd02\$oq6\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```mroc_1000 at hotmail.com (mroc) wrote in message news:<bopd02\$oq6\$1 at smc.vnet.net>...
> 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?

Maybe you should have given an explicit example?

In:=(* scalar function example : *)
scalarFunc[p1_,p2_,p3_,p4_]:=(p1+a*p2).(p3+b*p4);

In:=
scalarValue=scalarFunc[{p11,p12,p13},{p21,p22,p23},{p31,p32,p33},{p41,p42,p43}]
Out=(p11+a p21)(p31+b p41)+(p12+a p22)(p32+b p42)+(p13+a p23)(p33+b p43)

In:=D[scalarValue,a]
Out=p21(p31+b p41)+p22(p32+b p42)+p23(p33+b p43)

In:=(* vector function example : *)
vectorFunc[p1_,p2_,p3_,p4_]:=(p1+a*p2+p3+b^2*p4);
In:=
vectorValue=vectorFunc[{p11,p12,p13},{p21,p22,p23},{p31,p32,p33},{p41,p42,p43}]
Out={p11 + a p21 + p31 + b^2 p41, p12 + a p22 + p32 + b^2 p42,
p13 + a p23 + p33 + b^2 p43}

In:=D[vectorValue,b]
Out={2 b p41, 2 b p42, 2 b p43}
---
jcp

```

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