Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2004
*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 2004

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

Search the Archive

cross-product in cylindrical problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg51258] cross-product in cylindrical problem
  • From: "news" <anonym at bamboo.com>
  • Date: Sun, 10 Oct 2004 05:52:32 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

I'm really puzzled by this behavior of Mathematica, I have two vectors in 
cylindrical coordinates and would like to take their cross-product in 
cylindrical, but it seems to give me incorrect answer, see below:

define parametric path {r,phi,z}

In[110]:=
f[\[Rho]_, \[Phi]_] = {\[Rho], \[Phi], 0}
Out[110]=
{\[Rho], \[Phi], 0}

take derivates of path w.r.t. r then w.r.t phi, get {1,0,0}, and {0,1,0}

In[113]:=
v1 = D[f[\[Rho], \[Phi]], \[Rho]]
v2 = D[f[\[Rho], \[Phi]], \[Phi]]
Out[113]=
{1, 0, 0}
Out[114]=
{0, 1, 0}

then cross them in cylindrical coords, and should get {0,0,1}, but instead 
get wrong answer below

In[117]:=
n = CrossProduct[v1, v2, Cylindrical[\[Rho], \[Phi], z]] // FullSimplify
Out[117]=
{0, 0, 0}

As you can see, when I cross {1,0,0} with {0,1,0} in cylindrical coords, I 
get {0,0,0}, when I should be getting {0,0,1}.

Can anyone help?


  • Prev by Date: derivatives in cylindrical coords??
  • Next by Date: Re: Generating r-combination or r-permutations with replacement.
  • Previous by thread: derivatives in cylindrical coords??
  • Next by thread: Re: cross-product in cylindrical problem