On Wed, Aug 27, 2008 at 10:04 AM, Martin Albrecht <[EMAIL PROTECTED]> wrote: > > Hi there, > > Robert wrote at > > http://trac.sagemath.org/sage_trac/ticket/3956#comment:7 > > """ > Matrix hashes are specifically designed to be compatible with each other: > > {{{ > sage: M = random_matrix(GF(2), 10, 10) > sage: M.set_immutable() > sage: hash(M) > 561 > sage: MZ = M.change_ring(ZZ) > sage: MZ.set_immutable() > sage: hash(MZ) > 561 > sage: MS = M.spa > M.sparse_columns M.sparse_matrix M.sparse_rows > sage: MS = M.sparse_matrix() > sage: MS.set_immutable() > sage: hash(MS) > 561 > }}} > > This patch seems to break that. At a minimum, it seems sparse and dense > should hash to the same thing. If we want to change this policy, we should > at least ask on sage-devel. > """ > > I supplied a new patch for that ticket which fixes the issue in question. > > However, over at > > http://trac.sagemath.org/sage_trac/ticket/3724 > > there is a similar situation. Obeying Sage's hashing rules for GF(2) isn't as > straight forward as it is for #3956. Basically, we would have to decide > whether we want very fast hashs or consistent hashs. > > To feel the difference: > > sage: A = random_matrix(GF(3),8000,8000) > sage: A.set_immutable() > sage: %time hash(A) > CPU times: user 0.13 s, sys: 0.00 s, total: 0.13 s > Wall time: 0.14 s > 85210014 > > sage: A = random_matrix(GF(2),8000,8000) > sage: A.set_immutable() > sage: %time hash(A) > CPU times: user 0.00 s, sys: 0.00 s, total: 0.00 s > Wall time: 0.00 s > -7158142340691380618 > > sage: %timeit hash(A) > 100 loops, best of 3: 2 ms per loop > > > Thoughts?
I vote for fast. william --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
