I've been using a for loop with with mod functions to sieve number from the Natural numbers. Is there a more efficient sieve technique than this.
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My Code looks something like this
P = primes(100000);
N = 1999900000:1:2000000000;
for i = 1:numel(P);
N(mod(N,P(i))==P(i)+1) = [];
N(mod(N,P(i))==P(i)-1) = [];
end
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Answers (1)
Walter Roberson
on 1 Nov 2016
Certainly. You do not need to do the mod: you can mark off the multiples as being non-prime. https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
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Walter Roberson
on 2 Nov 2016
[n, p] = ndgrid(N, P);
is_composite = mod(n, p) == 0;
which_are_composite = any(is_composite, 1);
However, you had asked for a more efficient sieve technique, not one that would thrash your hard disk for a couple of days.
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