In the first one, you're checking all entries, not just upper-triangular ones. That'd account for a factor of 2 pretty well.
On Thu, 28 Jun 2007, Justin C. Walker wrote: > > Hi, > > I tried the following, added to the Matrix class definition in matrix/ > matrix0.pyx: > > def is_symmetric(self): > """ > Returns True if this is a symmetric matrix. > """ > if self._ncols != self._nrows: return False > cdef int i,j > for i from 1 <= i < self._nrows: > for j from 0 <= j < self._ncols: > if self[i,j] != self[j,i]: return False > return True > > While testing and timing this, I tried the following, out of a > perverse sort of curiosity: > > def is_sym3(self): > """ > Returns True if this is a symmetric matrix. > """ > if self._ncols != self._nrows: return False > for i in xrange(1,self._nrows): > for j in xrange(0,i): > if self[i,j] != self[j,i]: return False > return True > > Turns out that this, both as a method in the Matrix class and as a > raw hunk of python code, performs better than the above: > > sage: time Doit1(M2,1000) > CPU times: user 37.21 s, sys: 0.24 s, total: 37.45 s > Wall time: 38.10 > > sage: time Doit2(M2,1000) > CPU times: user 23.50 s, sys: 0.18 s, total: 23.68 s > Wall time: 24.55 > > sage: time Doit1(M3,1000) > CPU times: user 55.87 s, sys: 0.41 s, total: 56.29 s > Wall time: 58.48 > > sage: time Doit2(M3,1000) > CPU times: user 31.52 s, sys: 0.23 s, total: 31.76 s > Wall time: 32.83 > > sage: time Doit1(M4,1000) > CPU times: user 58.94 s, sys: 0.71 s, total: 59.65 s > Wall time: 63.05 > > sage: time Doit2(M4,1000) > CPU times: user 32.64 s, sys: 0.43 s, total: 33.08 s > Wall time: 35.05 > > > Doit1 is a loop that calls ".is_symmetric()", for the given count. > > Doit2 is a loop that calls "issym()", for the given count. > > M2 is a 200x200 integer symmetric matrix, with entries in the range > 1..300000. > > M3 is a 200x200 integer symmetric matrix, with entries in the range > 1..200000000000000000. > > M4 is a 200x200 integer symmetric matrix, with entries in the range > 1..2000000000000000000000000000000000000000000000000000000. > > Expected? Unexpected? > > Justin > > -- > Justin C. Walker, Curmudgeon-at-Large > () The ASCII Ribbon Campaign > /\ Help Cure HTML Email > > > > > > > --~--~---------~--~----~------------~-------~--~----~ 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://sage.scipy.org/sage/ and http://modular.math.washington.edu/sage/ -~----------~----~----~----~------~----~------~--~---
