[Numpy-discussion] permutation symbol

Charles R Harris charlesr.harris at gmail.com
Tue Jun 30 12:27:05 EDT 2009

On Tue, Jun 30, 2009 at 5:11 AM, Nils Wagner
<nwagner at iam.uni-stuttgart.de>wrote:

> On Tue, 30 Jun 2009 11:22:34 +0200
>  "Nils Wagner" <nwagner at iam.uni-stuttgart.de> wrote:
>>  Hi all,
>> How can I build the following product with numpy
>> q_i = \varepsilon_{ijk} q_{kj}
>> where  \varepsilon_{ijk} denotes the permutation symbol.
>> Nils
>  Sorry for replying to myself.
> The permutation symbol is also known as the Levi-Civita symbol.
> I found an explicit expression at
> http://en.wikipedia.org/wiki/Levi-Civita_symbol
> How do I build the product of the Levi-Civita symbol \varepsilon_{ijk} and
> the two dimensional array
> q_{kj}, i,j,k = 1,2,3 ?

Write it out explicitly. It essentially antisymmetrizes q and the three off
diagonal elements can then be treated as a vector. Depending on how q is
formed and the resulting vector is used there may be other things you can do
when you use it in a more general expression. If this is part of a general
calculation there might be other ways of expressing it.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/numpy-discussion/attachments/20090630/3dd43e3d/attachment.html>

More information about the NumPy-Discussion mailing list