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

  • To: mathgroup at
  • Subject: [mg44502] Re: Derivative of a funtion evaluated at a point in 3D
  • From: poujadej at (Jean-Claude Poujade)
  • Date: Wed, 12 Nov 2003 08:02:06 -0500 (EST)
  • References: <boign7$oj1$> <bopd02$oq6$>
  • Sender: owner-wri-mathgroup at

mroc_1000 at (mroc) wrote in message news:<bopd02$oq6$1 at>...
> mroc_1000 at (mroc) wrote in message news:<boign7$oj1$1 at>...
> > 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?
I hope this can help you :

In[1]:=(* scalar function example : *)

Out[2]=(p11+a p21)(p31+b p41)+(p12+a p22)(p32+b p42)+(p13+a p23)(p33+b p43)

Out[3]=p21(p31+b p41)+p22(p32+b p42)+p23(p33+b p43)

In[4]:=(* vector function example : *)
Out[5]={p11 + a p21 + p31 + b^2 p41, p12 + a p22 + p32 + b^2 p42, 
    p13 + a p23 + p33 + b^2 p43}

Out[6]={2 b p41, 2 b p42, 2 b p43}

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