Remember the thread "how to rotate a matrix by 45 degrees"? Here's
Oleg's solution (from
http://www.jsoftware.com/pipermail/general/2006-April/026991.html ):
M =: (,~ $ 0:)@(+:&.<:)@# NB. zero result matrix
N =: ,@(,~&.> |."1)@(+/~)@[EMAIL PROTECTED] NB. source
indices
rot =: (,`N`M)@]}~
Combining this with Jose's involute2 :
involute2 =: ([ $ /:@(+/\@(,@(] {. |:@((1 0 + [EMAIL PROTECTED]@|.)@[)) # +:@]
$ (, -)@(1 , {:@[)))) {.
We get:
tetspi =: rot@:(*/ - involute2)
tetspi 5 5
0 0 0 0 21 0 0 0 0
0 0 0 22 0 20 0 0 0
0 0 23 0 7 0 19 0 0
0 24 0 8 0 6 0 18 0
25 0 9 0 1 0 5 0 17
0 10 0 2 0 4 0 16 0
0 0 11 0 3 0 15 0 0
0 0 0 12 0 14 0 0 0
0 0 0 0 13 0 0 0 0
load 'viewmat'
viewmat rot@:(*/ - involute2) 500 500
Your job is to generate this is a cooler/faster/better way.
-Dan
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