datadataeverywhere comments on How Many LHC Failures Is Too Many? - Less Wrong

16 Post author: Eliezer_Yudkowsky 20 September 2008 09:38PM

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Comment author: wedrifid 30 September 2010 01:43:13AM *  0 points [-]

A uniform randomization may not be possible but you can get an arbitrarily well randomized list in linear time. That is all that is needed for the purposes of the sorting. (You would just end up destroying the world 1 + (1 / arbitrarily large) as many times as with a uniform distribution.)

Comment author: datadataeverywhere 30 September 2010 02:28:33AM *  2 points [-]

Algorithms like a modified Fisher-Yates shuffle in linear time if you're just measuring reads and writes, but O(lg(n!)) > O(n) bits are required to specify which permutation is being chosen, so unless generating random numbers is free, shuffling is always O(n log n) .

In real life, we don't use PRNGs with sufficiently long cycle times, so we usually get linear-time shuffles by discarding the vast majority of the potential orderings.