I'm not quite sure I follow what you are doing here. Shouldn't 2p1 be a neutral rotation, with 1p1 being a reversal of direction?
Thanks, -- Raul On Thu, Feb 18, 2016 at 10:23 PM, Louis de Forcrand <[email protected]> wrote: > To continue with the rotation challenges, write a verb that rotates a linear > polynomial (coeffs in x) by 0 {:: y with a centre of 1 {:: y: > > 1 2 linrot 1p1 ; 0 1 > 1 2 > 1 2 linrot 1r2p1 ; 0 1 > 1 _0.5 > 1 2 linrot 1p1;1 1 > _3 2 > > My take: > linrot=: ({: %. 1 ,. {.)@rotposmat > rotposmat=: centre + j./@posmat |:@:+.@:* r.@angle > centre=: 1&({::)@] > posmat=: (] ,: p.)&0 1@[ - centre > angle=: 0&({::)@] > > It uses matrix division on a rotated set of two points from the original > polynomial. Not very elegant, but I’m pretty sure it works. > > Best regards, > Louis > >> On 17 Feb 2016, at 06:40, Kip Murray <[email protected]> wrote: >> >> Not bad. I didn't know about r. . For clean I use >> >> clean =: (* *!.1e_14@|)"0&.+. >> >> --Kip >> >> On Tuesday, February 16, 2016, Raul Miller <[email protected] >> <mailto:[email protected]>> wrote: >> >>> Well... >>> >>> rottheta=: (rot~ r.)~ >>> 1r2p1 rottheta 3 4 >>> _4 3 >>> 1r4p1 rottheta _1 1 >>> _1.41421 1.11022e_16 >>> >>> I remember there being a concise phrase to clean irrelevant bits near >>> zero in a complex number, but I can't remember what I need to search >>> on to find it, and my foggy memory of how to write it is failing me at >>> the moment. >>> >>> Still, this gets you close. >>> >>> -- >>> Raul >>> >>> >>> On Tue, Feb 16, 2016 at 11:50 PM, Kip Murray <[email protected] >>> <javascript:;>> wrote: >>>> I'm retired with time to "fool around". Finding an old rot90 verb that >>>> used multiplication by a 2 by 2 matrix, I sought a more direct way using >>>> complex numbers and found one of the solutions that was posted. I also >>>> learned a lot from the other solutions posted, thanks everyone! >>>> >>>> New puzzle: find a complex analysis way to do a rotation given its angle >>> in >>>> radians, examples: >>>> >>>> 1r2p1 rottheta 3 4 >>>> _4 3 >>>> >>>> 1r4p1 rottheta _1 1 >>>> _1.414213562 0 >>>> >>>> --Kip >>>> >>>> I'm also a former math professor! >>>> >>>> On Tuesday, February 16, 2016, David Lambert <[email protected] >>> <javascript:;>> wrote: >>>> >>>>> >>>>> what's your agenda, are you writing a book? Isn't there a homogeneous >>>>> coordinate system/transformation lab? >>>>> >>>>>> >>>>>> On 02/16/2016 06:16 PM, [email protected] >>> <javascript:;> wrote: >>>>>> >>>>>>> Date: Tue, 16 Feb 2016 15:18:43 -0600 >>>>>>> From: Kip Murray<[email protected] <javascript:;>> >>>>>>> To:"[email protected] <javascript:;>" < >>> [email protected] <javascript:;>> >>>>>>> Subject: [Jprogramming] A plane rotation >>>>>>> Message-ID: >>>>>>> < >>> caofworgvydb1nmjwxkb0wosyfnlubxcdz20sv11uksfcfay...@mail.gmail.com >>> <javascript:;>> >>>>>>> Content-Type: text/plain; charset=UTF-8 >>>>>>> >>>>>>> Fairly easy: write a verb that rotates a point in the plane by the >>> angle >>>>>>> of >>>>>>> a given complex number. For example >>>>>>> >>>>>>> 1j1 rot 1 1 NB. Rotate 1 1 counterclockwise 45 degrees >>>>>>> 0 1.414213562 >>>>>>> >>>>>>> Background information: when you multiply two complex numbers the >>>>>>> magnitudes are multiplied and the angles are added. >>>>>>> >>>>>>> --Kip Murray >>>>>>> >>>>>>> >>>>>> >>>>> ---------------------------------------------------------------------- >>>>> For information about J forums see http://www.jsoftware.com/forums.htm >>>> >>>> >>>> >>>> -- >>>> Sent from Gmail Mobile >>>> ---------------------------------------------------------------------- >>>> For information about J forums see http://www.jsoftware.com/forums.htm >>> ---------------------------------------------------------------------- >>> For information about J forums see http://www.jsoftware.com/forums.htm >> >> >> >> -- >> Sent from Gmail Mobile >> ---------------------------------------------------------------------- >> For information about J forums see http://www.jsoftware.com/forums.htm >> <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
