On Jan 19, 2009, at 3:41 PM, slabbe wrote: > Hi! > > I would like to know if the following is a bug or if I have to work > with it. > > It is related to this conversation : > Finding a duplicated vector in a list of vectors > http://groups.google.com/group/sage-support/browse_thread/thread/ > 714bd13c9b36f683# > > Thank you, > > Sébastien Labbé > > ********* > > sage: hash(0) > 0 > sage: hash(SR(0)) > 0 > sage: hash(x-x) > 1849051185 > sage: hash(sqrt(2)-sqrt(2)) > 1849051185 > sage: hash(RR(0)) > 0 > sage: hash(ZZ(0)) > 0 > sage: hash(4-4) > 0 > sage: hash(sqrt(2)^2-1) > 1977051568
I assume that last one was meant to be sage: hash(sqrt(2)^2 - 2) 1849051185 In general the problem of representing symbolic expressions in a canonical form is unsolved (or may be undecidable in some cases), but all of these are trivially equal to 0. In general, I might evaluate the symbolic expressions at a random point, sort, and compare ones that looked "close enough" symbolically trying to prove equality. - Robert --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to sage-devel-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
