It doesn't seem right. But it is an inverse. 3+inv 3+4 4 3+3+inv 4 4
But inverse really has meaning only for monads. In order to make a dyad a monad J bonds the left argument to the verb. Perhaps bonding the right argument would give the answer you expected. like this: plus=:(+) :. (-&]) 3 plus inv 4 _1 (3 plus 4)plus inv 4 3 (3 plus inv 4)plus 4 3 And it works too for dyadic. But then it doesn't follow the right-to-left processing of verbs. 3 plus inv 3 plus 4 _4 3 plus 3 plus inv 4 2 Which is probably why bonding to the left was chosen. It fails for monadic. plus inv 3j4 _3j_4 plus could be defined as: plus=:(+) :. (+ : -) to avoid that monadic problem. Mathematics only defines inverse for monadic functions. At least as best as I can tell. Somewhere I saw that "inverse" could also be called "undo". But undo what? And it gets even messier if the verb/function is not commutative. And J's inverse is not always right either. *: inv *:_2 2 On Fri, Jan 9, 2015 at 11:25 AM, Linda Alvord <lindaalv...@verizon.net> wrote: > But 1 is the wrong answer ass a mathematician in the real world for the > answer for an inverse! > > 4*inv 7 > 1.75 > 4 * inv 7 > 1.75 > 4%7 > 0.571429 > 7%4 > 1.75 > > 4 + inv 7 > 3 > 4-7 > _3 > 7-4 > 3 > > Linda > > -----Original Message----- > From: programming-boun...@forums.jsoftware.com > [mailto:programming-boun...@forums.jsoftware.com] On Behalf Of Don Guinn > Sent: Thursday, January 8, 2015 12:06 PM > To: Programming forum > Subject: Re: [Jprogramming] A striggle with "inverse" > > Obverse/inverse applies to the monadic use of a verb. So, > > + b._1 NB. Conjugate > + > - b._1 NB. Negation > - > * b._1 NB. Signum. Cannot undo this. > |domain error > | *b._1 > % b._1 NB. Inverse > % > > When applied to a dyadic use it is interpreted as the left argument bound > to > the verb making a monadic verb. > > 3+inv 4 > > 1 > (3&+)b._1 > _3&+ > ---------------------------------------------------------------------- > 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
