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Re: differentiation of cross products

  • To: mathgroup at smc.vnet.net
  • Subject: [mg16534] Re: differentiation of cross products
  • From: "Peltio" <pelt.ioNOS at PAMiol.it>
  • Date: Tue, 16 Mar 1999 04:00:12 -0500
  • Organization: Peltio Inc.
  • References: <7cd2ol$nmc@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Issac,
a rude way to do  what you want is

Unprotect[Cross];
Cross /: D[Cross[f1_,f2_],x_]:=Cross[D[f1,x],f2]+Cross[f1,D[f2,x]]
Protect[Cross];

try it

D[Cross[g[t],h[t]],t]
    Cross[g'[t], h[t]] + Cross[g[t], h'[t]]

Hope that helps,
Peltio,
peltioNOS at PAMusa.net


Issac Trotts wrote in message <7cd2ol$nmc at smc.vnet.net>...
>Can anyone tell me how to differentiate the cross product
>of two vector-valued functions in Mathematica?
>The input
>
>D[Cross[g[t],h[t]],t]
>
>results in the output
>
>h'[t] Cross^(0,1)[g[t], h[t]] + g'[t] Cross^(1,0)[g[t], h[t]]
>
>which is not correct.  The correct answer would be
>
>Cross[g'[t], h[t]] + Cross[g[t], h'[t]]
>
>P.S.: Please send your response to trotts at ucdavis.edu .





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