2014-10-06 23:00 GMT+02:00 François Dumont <frs.dum...@gmail.com>: > On 05/10/2014 22:54, Marc Glisse wrote: >> >> On Sun, 5 Oct 2014, François Dumont wrote: >> >>> I took a look at PR 61217 regarding pop_heap complexity guarantee. >>> Looks like we have no test to check complexity of our algos so I start >>> writing some starting with the heap operations. I found no issue with >>> make_heap, push_heap and pop_heap despite what the bug report is saying >>> however the attached testcase for sort_heap is failing. >>> >>> Standard is saying std::sort_heap shall use less than N * log(N) >>> comparisons but with my test using 1000 random values the test is showing: >>> >>> 8687 comparisons on 6907.76 max allowed >>> >>> Is this a known issue of sort_heap ? Do you confirm that the test is >>> valid ? >> >> I would first look for confirmation that the standard didn't just forget a >> big-O or something. I would expect an implementation as n calls to pop_heap >> to be legal, and if pop_heap makes 2*log(n) comparisons, that naively sums >> to too much. And I don't expect the standard to contain an advanced >> amortized analysis or anything like that... >> > Good point, with n calls to pop_heap it means that limit must be 2*log(1) + > 2*log(2) +... + 2*log(n) which is 2*log(n!) and which is also necessarily < > 2*n*log(n). I guess Standard comittee has forgotten the factor 2 in the > limit so this is what I am using as limit in the final test, unless someone > prefer the stricter 2*log(n!) ?
François, could you please submit a corresponding LWG issue by sending an email using the recipe described here: http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#submit_issue ? Thanks, - Daniel