On Tue, 30 Jun 2009 10:27:05 -0600 Charles R Harris <[email protected]> wrote: > On Tue, Jun 30, 2009 at 5:11 AM, Nils Wagner > <[email protected]>wrote: > >> On Tue, 30 Jun 2009 11:22:34 +0200 >> "Nils Wagner" <[email protected]> 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. > > Chuck Hi Chuck,
Thank you for your response. The problem at hand is described in a paper by Angeles namely equation (17c) in "Automatic computation of the screw parameters of rigid-body motions. Part I: Finitely-separated positions" Journal of Dynamic systems, Measurement and Control, Vol. 108 (1986) pp. 32-38 I am looking for a pythonic implementation of the algorithm. Nils _______________________________________________ Numpy-discussion mailing list [email protected] http://mail.scipy.org/mailman/listinfo/numpy-discussion
