I'm seeing strange behavior with sparse arrays, and I have been mostly
unsuccessful in simplifying code exhibiting the problem. Thus:
pritch=: {{
spokes=. $.,1
primes=. i.0
while. y > #spokes do.
primes=. primes, p=. 2+(}.spokes) i.1 NB. find next prime
rim=. #spokes NB. "length" of "circumference" of wheel
spokes=. (y<.p*rim)$spokes NB. roll next larger wheel
spokes=. 0 ((#~ y>])_1+p*1+i.rim)} spokes
end.
NB. elided code here
primes,1+}.,I.spokes
}}
pritchard 20
2 3 5 7 11 13 17 19
pritch8=: {{
spokes=. $.,1
primes=. i.0
while. y > #spokes do.
primes=. primes, p=. 2+(}.spokes) i.1 NB. find next prime
rim=. #spokes NB. "length" of "circumference" of wheel
spokes=. (y<.p*rim)$spokes NB. roll next larger wheel
spokes=. 8 $. 0 ((#~ y>])_1+p*1+i.rim)} spokes
end. NB. elided code here
primes,1+}.,I.spokes
}}
pritch8 20
2 2 3 5 7 11 13 17 19
Somehow the value for p is different when 8 $. is present in this
particular implementation (though I don't observe similar behavior in
similar uses of 8 $. y).
I'm reporting this on the beta forum, but it's an issue in J903 (and,
probably, earlier versions of J).
FYI,
--
Raul
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