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Re^3: ulam's spiral too slow

by liverpole (Monsignor)
on Apr 16, 2007 at 12:53 UTC ( #610337=note: print w/replies, xml ) Need Help??

in reply to Re^2: ulam's spiral too slow
in thread ulam's spiral too slow

Thanks for catching that.  I just noticed the bug in my code, which is:  although I'm caching prime numbers, I'm not testing all of them as potential factors.

I'll go update the code now, but you're right; there needs to be a check for division by 2.


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Re^4: ulam's spiral too slow
by orange (Beadle) on Apr 17, 2007 at 07:22 UTC
    thanks, your code is much faster than mine, and now it produce the same figure as in the
    after we invert the colors
    one small note is that your code will plot number 1 as a prime number, we can find this if we insert
    print "number of primes = $NumOfPrimes \n"; before the mainloop; and try the program with number 10 , it will give us the number of primes is 5
    as a variation i suggest for the invistigators for small spirals to replace the main plotting code:
    $c->createText( $x*+$o, $y+$o, -fill => "$colr", -text => '.'); with
    $c->createText( $x*30+$o, $y*30+$o, -fill => "$colr", -text => "$num"); so we can see numbers instead of dots in wich the primes will be in white color , the factor 30 above is for magnification of the plotting.

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