> Roger, can you shed any light? The current choice of the monad u;.0 is minor as it is just one instance of a more general dyadic case. I don't know why Ken made this choice (reversing each axis). Perhaps it was motivated by something from tensor analysis.
----- Original Message ----- From: Dan Bron <[EMAIL PROTECTED]> Date: Friday, June 20, 2008 14:16 Subject: RE: [Jprogramming] Apply to all axis To: Programming forum <[email protected]> > RE Boss asked: > > why "reversing y along each axis" was > > introduced in defining ;.0 > > My quick search didn't turn up a rationale, but in response to > your (RE Boss') "Reversing all ranks" thread, which I linked to > earlier, Roger had this to say: > > Ken told me that sometimes, when > he came up with a neat > solution to a problem, he'd be > accused of putting in > a special construct in the > language just for that problem. > (And that was why the solution > was so neat.) But the > accusation lost its sting when it > was repeated in problem > after problem, in multiple > diverse fields. > > (From > http://www.jsoftware.com/pipermail/programming/2005-December/000322.html ) > > As I read it, it was posted more-or-less in defense of the > definition of ;.0 , so maybe Ken saw this (reversing > all ranks) as a recurring problem. Roger, can you shed any > light? > Actually, RE Boss, maybe you can. You started that thread > by asking for a replacement for |."3@:(|."2)@:(|."1) > . Do you remember why you wanted to do that? I > personally have not seen this problem recur in field after field. > > In fact, after some research earlier today, it seems the > recurring "all ranks" problem is in fact the one that started > this thread: padding an array on all dimensions. > Trimming (the opposite of padding) an array on all dimensions > came in second. > > -Dan > > PS: I don't remember ever wanting to "reverse all ranks", > but I have wanted an "alternating reversal" sometimes. > That is, I wanted to reverse every other item of an array. > One of my prouder J moments was discovering (A."_1~ > _2 | i.@:#) for this purpose. There are other ways, too: > > > http://www.jsoftware.com/pipermail/programming/2006-November/004198.html ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
