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Re^3: Algorithm for cancelling common factors between two lists of multiplicands

by hv (Parson)
on Aug 09, 2005 at 00:07 UTC ( #482073=note: print w/replies, xml ) Need Help??


in reply to Re^2: Algorithm for cancelling common factors between two lists of multiplicands
in thread Algorithm for cancelling common factors between two lists of multiplicands

For simple problems I usually use something like this:

{ my @p; BEGIN { @p = (2, 3) } sub nextprime { my $p = $p[$#p]; DIV: while (1) { $p += 2; my $pc = 0; while (1) { my $d = $p[$pc++]; last if $d * $d > $p; next DIV unless $p % $d; } $p[@p] = $p; return $p; } } sub factors { my $n = shift; my($pc, @result) = (0); while ($n > 1) { my $d = $p[$pc++] || nextprime(); if ($d * $d > $n) { push @result, $n; $n = 1; } else { while ($n % $d == 0) { $n /= $d; push @result, $d; } } } \@result; } }

The rest of the time I use Math::Big*, sometimes with Pari or (lately) GMP.

Hugo

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Re^4: Algorithm for cancelling common factors between two lists of multiplicands
by BrowserUk (Pope) on Aug 09, 2005 at 00:27 UTC

    Nice, thankyou. I like nextPrime(). I was kludging something together by embedding the first 1000 primes in a DATA section.


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