User talk:WillNess: Difference between revisions
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::::::: Ah, great, thanks for that. Yes, I understand the space leak here, that's why I wrote those other versions back then; just thought ''maybe'' they fixed it by now with the newer GHC somehow. You're right, all this should be made clear in the text. -- [[User:WillNess|WillNess]] ([[User talk:WillNess|talk]]) 10:34, 22 August 2016 (UTC)
::::::: I've tried it locally, and it reports "234MB memory in use" for 1B and 1187MB for the 10B. I don't understand what is this 7.8MB figure that Ideone shows for both. I was misled by this. -- [[User:WillNess|WillNess]] ([[User talk:WillNess|talk]]) 10:45, 22 August 2016 (UTC)
::::::: BTW the really short version of it is just <code>(Sum c,b) = mconcat [ ( Sum (i+1), ...</code>. Here it could be argued that it '''''ought''''' to be compiled efficiently, as the whole premise of Monoids is that associativity enables re-parenthesization ''(<code>a:b:c:... = [a]++([b]++([c]++...)) = ([a]++[b])++([c]++...)</code>)'', which is the basis for the efficiency of the strict left fold. Yet it is more than twice worse than the <code>prod</code> code, both in time and space.
::::::: BTW, I got 1B:0.45s-269MB and 10B:1.75s-1343MB, which suggests 1T:38s-'''28.8GB''' ''"total memory in use"''. The fold-based version indeed did good at 1T:11.2s-'''10MB'''. I use the signature <code>Int -> (Double, (Int,Int,Int))</code> which produced the fastest code in my tests (simple -O2). -- [[User:WillNess|WillNess]] ([[User talk:WillNess|talk]]) 17:13, 22 August 2016 (UTC)
:::::::: Looks good; it's still about three times slower and uses more memory than 1T:3.75s:3MB "total memory in use" (from local) as for my version on IdeOne but it is good as referents will have a choice. I went back to using Word64 as the fastest (just a slightly higher range than Int) even for 32-bit code as it is faster, since it then uses the same type for the internal count. it looks like for all the Monoid stuff to work as you would like to see it there will have to be all kinds of specializations that haven't been added - complex stuff, and doing "concat" efficiently has always been a headache. --[[User:GordonBGood|GordonBGood]] ([[User talk:GordonBGood|talk]]) 00:50, 23 August 2016 (UTC)
== Factors of an integer ==
The current algorithms factors_co and factors_o seem to give the wrong result. For example, factors_co 120 is missing the number 12 in its result. --[[User:Helge|Helge]] ([[User talk:Helge|talk]]) 13:15, 26 December 2016 (UTC)
: Good catch, thanks! Will fix. -- [[User:WillNess|WillNess]] ([[User talk:WillNess|talk]]) 21:06, 26 December 2016 (UTC)
: Done! Thanks again for spotting this. An added bonus was, the code simplified a bit, too. -- [[User:WillNess|WillNess]] ([[User talk:WillNess|talk]]) 07:43, 27 December 2016 (UTC)
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