You can get help from Phrases for extracting diagonal elements. See the bottom half of this page:
http://www.jsoftware.com/docs/help701/phrases/special_matrices.htm Kip Murray Sent from my iPad On Nov 18, 2012, at 7:51 PM, Don & Cathy Kelly <d...@shaw.ca> wrote: > This also helped me where I wanted to extract the diagonal elements of an > array! > I was trying for a neater way to do it but as in the end, I have to do it > several times, it appears that it is easier to establish a unit matrix and > then use this each time I want to deal with a matrix of the same size > rather than using (* =@i.@#) y and repeating for different y or using the > cap as you suggest, I can simply define a unit matrix U > and then us U*y as needed. > > Still very hit and miss on the multiple ways to skin a cat in J > > Don Kelly > > > > On 15/11/2012 9:55 PM, bob therriault wrote: >> Hey Vijay, >> >> Nothing wrong with a novice question, especially when it is so clearly >> phrased. >> >> Take a look at these examples and see if this gives you some ideas. >> >> fact1=: */@:>:@:i. >> fact1 5 >> 120 >> fact2=: [:*/>:@:i. >> fact2 5 >> 120 >> fact3=: [:*/[:>:i. >> fact3 5 >> 120 >> >> You want to have the verbs act sequentially on the argument and your >> original definition is a fork which has the outside verbs act on the >> argument and then send the results to the left and the right of the centre >> verb. >> (v1 v2 v3) y is actually ((v1 y) v2 (v3 y)). In this case (*/ >: i.) 5 >> becomes ((*/ 5) >: (i. 5)) and then (5 >: 0 1 2 3 4) which becomes 1 1 1 1 1 >> >> A good reference link would be >> http://www.jsoftware.com/jwiki/Guides/Language%20FAQ#Guides.2FLanguage_FAQ.2FSentence_Train.Why_.2B-.2F_.2A:_a_works.2C_but_when_I_say_foo_.3D:_.2B-.2F_.2A:.2C_foo_a_doesn.27t_work.3F >> >> Hope this helps. There is a lot to this language, even when you have been >> playing with it for a while, so keep at it. >> >> Cheers, bob >> >> On 2012-11-15, at 9:20 PM, Vijay Lulla wrote: >> >>> Please forgive me for asking a novice question. >>> >>> I tried >>> */>:i.5 NB. results in 120 >>> >>> But I define >>> fact=: */>:i. >>> fact 5 NB. results in 1 1 1 1 1 >>> >>> I remember reading about this somewhere but I cannot seem to find the >>> relevant pages now. Any pointers as to where I could find these documents >>> or a brief explanation (which can be easily remembered) will be very >>> helpful and is highly appreciated. >>> Thanks, >>> Vijay Lulla. >>> ---------------------------------------------------------------------- >>> 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 ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
