Nonsense. Assume the 4&$. refers to all 1's and one gets something useful. Make a specific fill item or items the other argument to the custom conjunction and it's all good, actually it's a one-sided inverse. ------------------------------------------------------------------------ |\/| Randy A MacDonald | APL: If you can say it, it's done.. (ram) |/\| [EMAIL PROTECTED] | |\ | | The only real problem with APL is that BSc(Math) UNBF'83 | it is "still ahead of its time." Sapere Aude | - Morten Kromberg Natural Born APL'er | Demo website: http://156.34.82.188/ -----------------------------------------------------(INTP)----{ gnat }-
----- Original Message ----- From: "Roger Hui" <[EMAIL PROTECTED]> To: "Programming forum" <[email protected]> Sent: Saturday, February 03, 2007 2:21 PM Subject: Re: [Jprogramming] Spare Matrix from Index Matrix > For all the following arrays the non-zero elements > are the same, viz., 1 , and 4$.s are also the same, > viz., i.4 1 > s0=: (2;0)$.4 5$1 > s1=: (2;0)$.4 7$1 > s2=: $. 4$1 > s3=: (2;1)$.7 4$1 > s4=: (2;0)$. 100 200{.4 5$1 > but there is no way to recover s from 4$.s . > > 4$.s is not invertible. > > > > ----- Original Message ----- > From: ramacd <[EMAIL PROTECTED]> > Date: Saturday, February 3, 2007 9:05 am > Subject: Re: [Jprogramming] Spare Matrix from Index Matrix > > > True, if an assumption is missing about the non-zero element. I > > suggest 1. > > > > > ----- Original Message ----- > > From: "Roger Hui" <[EMAIL PROTECTED]> > > To: "Programming forum" <[email protected]> > > Sent: Saturday, February 03, 2007 10:07 AM > > Subject: Re: [Jprogramming] Spare Matrix from Index Matrix > > > > > > > 4$.s is not invertible. > > > > > > > > > > > > ----- Original Message ----- > > > From: ramacd <[EMAIL PROTECTED]> > > > Date: Saturday, February 3, 2007 6:07 am > > > Subject: Re: [Jprogramming] Spare Matrix from Index Matrix > > > > > > > It seems Roger is a mortal; > > > > > > > > s=: ?4 4$2 > > > > (4&$.)^:_1 (4 $. s) > > > > |domain error > > > > (4&$.)^:_1(4 $.s) > > > > > > > > ...or is my copy of J too old? > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
