Alan
>when i first read your note i reinterpreted it as the prime ness of half of
>the midpoint of prime pairs (ie off by two from each other)... i suppose this
>is a made up question which i am guilty of providing exploratory functions for:
ps=: p:@i. NB. primes
pp=: ((2&+) = (1&|.)) NB. prime pair?
pq=:1&p: NB. prime?
ek=: </. NB. enclose key
dl=: >@{: NB. disclose last
pip=:(>@{:) @(pp </. ])@ps
hi=: -:@>: NB. halve inc
hpp=: >@}:@(pq ek ]) @ (-:@>:@pip) NB. half primes of pairs
NB. this works responsively on my machine for up to
hpp 1e7
2 3
NB. hpp 1e8 gives the same slowly ,and hpp 1e9 gives out of memory
NB. Except for the first two pairs, it appears that none work...
greg
~krsnadas.org
--
from: R.E. Boss <[email protected]>
to: [email protected]
date: 12 May 2013 08:56
subject: Re: [Jprogramming] Testing consecutive pairs of primes
All the boxing is unnecessary.
Here is the performance you win (j801):
ts'+/>1&p: each 2 %~ each +/ each (2 <\ ])p: i. 1000000'
6.4344903 1.8283457e9
ts' +/1 p:2%~ 2 +/\ p: i. 1000000'
0.38894168 1.9701402e8
Rule of thumb: don't box items of same shape.
R.E. Boss
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