On Tuesday, November 4, 2014 9:52:03 AM UTC-8, kcrisman wrote: > > Interesting. Since this assumption stuff does something in Maxima, > perhaps that is where the slowdown happens. I'm not sure that we ask > Maxima to check for our equality, though perhaps it comes into play once > that assumption is made. >
Sage apparently does not call Maxima for this, since is(equal(0,exp(512*(x+1)))); takes 0.05ms, even if one provides the irrelevant declare(x,real). Or if it calls Maxima, it does something else for quite a while. RJF > > > >> Hi, >> >> I know that comparing symbolic expressions of a real variable is >> generally an undecidable problem, but I've recently faced the following CPU >> time issue on very simple symbolic expressions: >> >> sage: assume(x, 'real') >> sage: %time bool(exp(512*(x+1)) == 1) >> CPU times: user 4min 46s, sys: 116 ms, total: 4min 46s >> Wall time: 4min 48s >> False >> >> The CPU time actually increases with the factor in front of (x+1): >> >> sage: %time bool(exp(2*(x+1)) == 1) >> CPU times: user 24 ms, sys: 4 ms, total: 28 ms >> Wall time: 23.7 ms >> False >> sage: %time bool(exp(32*(x+1)) == 1) >> CPU times: user 108 ms, sys: 0 ns, total: 108 ms >> Wall time: 105 ms >> False >> sage: %time bool(exp(64*(x+1)) == 1) >> CPU times: user 660 ms, sys: 4 ms, total: 664 ms >> Wall time: 664 ms >> False >> sage: %time bool(exp(128*(x+1)) == 1) >> CPU times: user 4.2 s, sys: 0 ns, total: 4.2 s >> Wall time: 4.23 s >> False >> sage: %time bool(exp(256*(x+1)) == 1) >> CPU times: user 33.9 s, sys: 4 ms, total: 33.9 s >> Wall time: 34.1 s >> False >> >> If x is not assumed to be real, everything is fine: >> >> sage: forget() >> sage: %time bool(exp(512*(x+1)) == 1) >> CPU times: user 32 ms, sys: 0 ns, total: 32 ms >> Wall time: 31.7 ms >> False >> >> Thanks for your comments / advice on this. >> >> Eric. >> > -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
