Le mercredi 5 décembre 2012 23:54:24 UTC+1, Maarten Derickx a écrit : > > It seems that this is exactly the same problem of something I fixed for > general matrix construction earlier on. See: > http://trac.sagemath.org/sage_trac/ticket/10628 > > The problem is that the complexity of: sum(some_list_of_lists,[]) is > something like n^2*m where n = len(some_list_of_lists) and m is the length > of all lists contained in some_list_of_lists . This is because when adding > two lists python creates a new copy to store the new result. > If you first flatten your list of entries (so that it doesn't happen in > the cyclotomic field initialization code) the slowness should go away. > > I.e. do: > > tmp=[] > for v in entries: > tmp.extend(v) > entries = tmp > M = MatrixSpace(F,100)(entries) > > Maybe we should overwrite the sum() function such that it behaves > different for lists, since the command sum(entries,[]) looks much more > clear and intuitive then the for loop. >
It seems like the top level sum in sage is already optimized by doing some binary tree balances sum stuff, so maybe just importing that sum in the cyclotomic field code should also fix this performance issue. > > > Le mercredi 5 décembre 2012 19:36:07 UTC+1, Nils Bruin a écrit : >> >> >> >> On Wednesday, December 5, 2012 9:08:13 AM UTC-8, Volker Braun wrote: >>> >>> Of course fixing the cyclotomic matrix constructor would be another >>> option ;- >> >> In fact, John, please do! As your own "loop assignment" shows, the >> problem you're experiencing is not inherent to Matrix_cyclo_dense, it's >> just overhead in creating all these intermediate lists. It's >> straightforward to refactor that bit of code and you have a motivation for >> it now. >> >> Representing a dense matrix as sparse will break you up later, even if >> initial construction doesn't run into the same pitfall. >> > -- You received this message because you are subscribed to the Google Groups "sage-support" group. To post to this group, send email to sage-support@googlegroups.com. To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com. Visit this group at http://groups.google.com/group/sage-support?hl=en.
