Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2006
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2006

[Date Index] [Thread Index] [Author Index]

Search the Archive

Differentiating Cross

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66238] Differentiating Cross
  • From: "Vladimir" <vladimir347 at yahoo.com>
  • Date: Fri, 5 May 2006 05:02:27 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hello!

We have a handy default rule for Dot:

In[]:= Dt[a . b, t]

Out[]= a . Dt[b, t] + Dt[a, t] . b


So I'd like to have a similar behavior for Cross,
but it looks like chain rule is used instead:

In[]:= Dt[Cross[a, b], t]

Out[]= Dt[b, t]*Derivative[0, 1][Cross][a, b] +
          Dt[a, t]*Derivative[1, 0][Cross][a, b]


So I defined required transformation:

In[]:= Unprotect[Dt];
Dt[Cross[a_, b_], t_] := Cross[a, Dt[b, t]] + Cross[Dt[a, t], b];

which works for just Dt[Cross[a, b], t],
but it still doesn't work when Cross is a part
of expression like Dt[Cross[a, b] + c, t] etc.

What am I doing wrong?

--
Vladimir


  • Prev by Date: Re: Faster Random Walk Simulation ?!?
  • Next by Date: Mathematica 4.1 on ThinkPAD T40 - Exception ntdll.dll - any advice on how to fix?
  • Previous by thread: RootSearch package updated
  • Next by thread: Mathematica 4.1 on ThinkPAD T40 - Exception ntdll.dll - any advice on how to fix?