So: in Pablo's first version the problem was not in computing len(results), but in the comparison between that value (a Python int) and the Sage Integer cota, which involves creating a temporary Sage integer and then doing the comparison between two of those.
In Pablo's second version there is no conversion, but still two Sage integers are being compared. In Tom's version the variable cota is a python int so (since taking len() really is negligible!) the speedup comes from the speed of comparing two (very small) python ints. There is a lesson to be learned here, which is in fact very similar to one which William explained very well recently: beware the Sage preprocessor which converts every integer it sees to an Integer, which can have serious performance consequences and is often not necessary! John On Tue, Nov 23, 2010 at 4:44 PM, Tom Boothby <tomas.boot...@gmail.com> wrote: > The problem is not with len(), merely with the conversion from an int > to an Integer required in comparing len(results)<cota. > > The following code is faster than either of your versions. Note that > '3r' is an int, whereas '3' is an Integer. > > tri=pen=hex=dt=dp=dh=1r > results=[] > cota = 3r > while len(results)<cota: > if tri==pen==hex: > results.append(tri) > if tri<=pen and tri<=hex: > dt+=1r > tri+=dt > elif pen<=hex: > dp+=3r > pen+=dp > else: > dh+=4r > hex+=dh > print results > > On Tue, Nov 23, 2010 at 3:00 AM, Pablo Angulo <pablo.ang...@uam.es> wrote: >> Hello: >> A colleague was working in code for a certain projecteuler problem, >> and found that using "len" of a list has a severe penalty on the sage >> notebook, which doesn't happen on either the sage or the python console. >> The two versions of the code below differ only in a call to the function >> len. In console, the penalty in performance is around 10%, but in the >> Sage notebook, it takes 3 times longer: the call to "len" costs doble >> time as the rest of the loop. Anyway, we've been getting weird results >> from time and its family lately (like CPU time longer than Wall time: is >> that ok?). This is tested on versions 4.6 and 4.4, on different >> architectures. >> >> Regards >> >> Version 1 >> >> tri=pen=hex=dt=dp=dh=1 >> results=[] >> cota = 3 >> while len(results)<cota: >> if tri==pen==hex: >> results.append(tri) >> if tri<=pen and tri<=hex: >> dt+=1 >> tri+=dt >> elif pen<=hex: >> dp+=3; >> pen+=dp >> else: >> dh+=4; >> hex+=dh >> print results >> >> >> Version 2 >> >> cota = 3 >> tri=pen=hex=dt=dp=dh=1 >> results=[] >> n=0 >> while n<cota: >> if tri==pen==hex: >> results.append(tri) >> n+=1 >> if tri<=pen and tri<=hex: >> dt+=1 >> tri+=dt >> elif pen<=hex: >> dp+=3; >> pen+=dp >> else: >> dh+=4; >> hex+=dh >> print results >> >> -- >> To post to this group, send an email to sage-devel@googlegroups.com >> To unsubscribe from this group, send an email to >> sage-devel+unsubscr...@googlegroups.com >> For more options, visit this group at >> http://groups.google.com/group/sage-devel >> URL: http://www.sagemath.org >> > > -- > To post to this group, send an email to sage-devel@googlegroups.com > To unsubscribe from this group, send an email to > sage-devel+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/sage-devel > URL: http://www.sagemath.org > -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
