Roman Leshchinskiy wrote:
wren ng thornton wrote:
Roman Leshchinskiy wrote:
On 04/11/2009, at 13:23, Daniel Peebles wrote:
In the presence of fusion (as is the case in uvector), it's hard to
give meaningful time complexities for operations as they depend on
what operations they are paired with. We need to think of a better way
to express this behavior in the documentation though.
I have to disagree here. Fusion never makes the complexity of
operations worse. If it does, it's a bug.
I think the point was more that the relevant complexity bound can
change in the presence of fusion. For a poor example: the first map
over a list is O(n) but all subsequent ones in a chain of maps are
O(1) with fusion. I'm sure there are better examples than that, but
you get the idea. Some people may care to know about that latter
complexity rather than just the "independent" complexity.
I think asymptotic complexity is the wrong tool for what you're trying
to do. [...] Executing the two maps, be it one after another or interlocked,
is linear simply because O(n) + O(n) = O(n), not because of fusion.
As I said, it was a bad example. Off-hand I can't think of any examples
where fusion actually does affect asymptotic complexity rather than just
reducing the constant factor. But I think such examples (if they exist)
are what Daniel was concerned with, rather than any bugs where fusion
makes the complexity (or constant factors) worse.
--
Live well,
~wren
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