Hi Björn, This is a bit brute force but it seems to work. g=: i.~ f"0@:i.@:+: g 87 75
Essentially applying f to a list up to twice the argument (y) and returning the index (x) of the first spot f(x)=y Cheers, bob ps. I believe your original f can also be written as: f1=: [: # i. -./ 2 3 ^~ i. On 2010-12-26, at 11:47 AM, Björn Helgason wrote: > I have a small task that looks like this > > f=: [: # i. -. (2 ^~ i.) , 3 ^~ i. > f 87 > 75 > > I want to use tacit to find what number gives me 75 numbers (the answer > being 87) > > Could be asking what argument y do I need to find x numbers according to the > formula above > > -- > Björn Helgason, Verkfræðingur > Fornustekkum II > 781 Hornafirði, > t-póst: gos...@gmail.com > gsm: +3546985532 > sími: +3544781286 > 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 | > ( -. | `-----------------------------------' > | ) | (\_ _/) > (`-. '--.) (='.'=) ♖♘♗♕♔♙ > `. )----' (")_(") ☃☠ > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm