That is nice! Here is a slightly different variation
f=: 3 : 0 ((#y),(#y))$ y ((1+#y)* i. #y) } ,((#y),(#y))$ 0 ) f 2 7 9 20 2 0 0 0 0 7 0 0 0 0 9 0 0 0 0 20 2008/10/12 Mike Day <[EMAIL PROTECTED]> > This might well be in Roger's essay, but it's so > concise and beautiful that I can't resist sending > it anyway! > > (*=) 2 7 9 20 NB. I'm forcing a line throw > > 2 0 0 0 > 0 7 0 0 > 0 0 9 0 > 0 0 0 20 > > Mike > > > Roger Hui wrote: > >> http://www.jsoftware.com/jwiki/Essays/Identity_Matrix >> may give you some ideas. For the identity matrix itself >> there are over 30 ways. >> >> >> >> ----- Original Message ----- >> From: Raul Miller <[EMAIL PROTECTED]> >> Date: Saturday, October 11, 2008 11:40 >> Subject: [Jprogramming] diagonal arrays >> To: Programming forum <[email protected]> >> >> >> >>> Given a vector, put it on the diagonal of an array: >>> >>> (<0 1)&|:inv 2 7 9 20 >>> |index error >>> (+/ .*(e.(<0 1 2 )&|:)@i.@(3##)) 2 7 9 20 >>> 2 0 0 0 >>> 0 7 0 0 >>> 0 0 9 0 >>> 0 0 0 20 >>> (, $~ 2##)@(,"0 1*&0)2 7 9 20 >>> 2 0 0 0 >>> 0 7 0 0 >>> 0 0 9 0 >>> 0 0 0 20 >>> >>> Are there more concise approaches, that work? >>> >>> >> >> >> ---------------------------------------------------------------------- >> For information about J forums see http://www.jsoftware.com/forums.htm >> ------------------------------------------------------------------------ >> >> >> No virus found in this incoming message. >> Checked by AVG - http://www.avg.com Version: 8.0.173 / Virus Database: >> 270.8.0/1717 - Release Date: 09/10/2008 16:56 >> >> >> > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > -- Björn Helgason, Verkfræðingur Fugl&Fiskur ehf, Þerneyjarsundi 23, Hraunborgum Po Box 127,801 Selfoss , t-póst: [EMAIL PROTECTED] gsm: +3546985532 Landslags og skrúðgarðagerð, gröfuþjónusta http://groups.google.com/group/J-Programming Tæknikunnátta höndlar hið flókna, sköpunargáfa er meistari einfaldleikans góður kennari getur stigið á tær án þess að glansinn fari af skónum /|_ .-----------------------------------. ,' .\ / | Með léttri lund verður | ,--' _,' | Dagurinn í dag | / / | Enn betri en gærdagurinn | ( -. | `-----------------------------------' | ) | (\_ _/) (`-. '--.) (='.'=) `. )----' (")_(")
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