A little more polish: flipidm=: - =/&i. ] flipidm 4 0 0 0 1 0 0 1 0 0 1 0 0 1 0 0 0
> From: Lippu Esa > Sent: Friday, 20 August 2010 22:51 > > flipidm=...@-=/i. > > flipidm 4 > 0 0 0 1 > 0 0 1 0 > 0 1 0 0 > 1 0 0 0 > > Esa > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Stefano > Lanzavecchia > Sent: 20. elokuuta 2010 13:49 > To: 'Programming forum' > Subject: Re: [Jprogramming] Creating a matrix (some polish required) > > Once you know how to build the identity matrix (several ways on > http://www.jsoftware.com/help/phrases/special_matrices.htm) you reverse > it > (http://www.jsoftware.com/help/dictionary/d231.htm) and that's it. > > > -----Original Message----- > > From: [email protected] [mailto:programming- > > [email protected]] On Behalf Of Alex Gian > > Sent: Friday, August 20, 2010 12:41 PM > > To: Programming forum > > Subject: [Jprogramming] Creating a matrix (some polish required) > > > > The "flipped" identity matrix is quite interesting. (Basically it's > the > identity > > matrix flipped or mirrored about either the vertical or horizontal > axis. > IOW, > > for a 3x3: > > 0 0 1 > > 0 1 0 > > 1 0 0 > > I don't know if it has any special name, I stumbled on it by chance > while > > messing around with a simple FSA for a puzzle game. > > Pre-multiplying by this matrix flips any same size matrix vertically, > post- > > multiplying flips it horizontally. Its square is obviously the > identity > matrix. > > > > Now, I have created this matrix on various systems, (e.g. HP/RPL, > Scheme, > TI- > > Basic), usually - if an id matrix is provided - just by reversing its > rows, > > otherwise just by starting off with the vector, say, > > 0 0 0 1, and then rotating the "1" each time and appending that > vector > to > a > > string, which is eventually converted to a matrix. > > > > I can do this using loops and explicit coding, but am looking for any > > suggestions to make it into a J one-liner, such that: > > flipidm 4 > > 0 0 0 1 > > 0 0 1 0 > > 0 1 0 0 > > 1 0 0 0 > > > > Hope my explanation was clear enough, > > TIA > > > > > > > > --------------------------------------------------------------------- > - > > For information about J forums see > http://www.jsoftware.com/forums.htm > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
