joshuagrochow,
@joshuagrochow@mathstodon.xyz avatar

I love big-O notation when doing theory to focus on big ideas,

but constants can matter in practice, and often do!

(Leading constants moreso. To focus on leading constant but still ignore lower order terms you can use asymptotic equality ~)

(Inspired by @ccanonne on the birdiste.)

massimolauria,
@massimolauria@mathstodon.xyz avatar

@joshuagrochow @ccanonne I agree with the sentiment, and this is indeed what Robert Sedgewick and other highlight with their approach to the analysis of algorithm. Too bad is so hard to apply! PS: every time a theoretician says "in practice", I think to the "Young Mr Burns" meme...

ccanonne,
@ccanonne@mathstodon.xyz avatar

@joshuagrochow it also depends a lot on where the "hidden constant" shows up. "Achieving accuracy O(alpha) in time blah" means a hell of a different thing when the running time has a quadratic dependence on the accuracy than when it has an exponential one...

joshuagrochow,
@joshuagrochow@mathstodon.xyz avatar

@ccanonne Indeed! Also depends on how you use the big-Oh. e.g. in practice 𝑂(2ⁿ) can be way better or way worse than 2ᴼ⁽ⁿ⁾ (depending primarily, but not entirely, on the hidden constant in the latter!).

A big-Oh that hides a factor of 2 in elementary operations might not be so important. But a big-Oh that allows you to ignore finitely many cases, which includes all cases up to size 1billion is a big deal.

ccanonne,
@ccanonne@mathstodon.xyz avatar

@joshuagrochow I always start my recurrence relations at n=2⁹⁷⁵.

joshuagrochow,
@joshuagrochow@mathstodon.xyz avatar
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