On Mon, Feb 15, 2010 at 1:19 PM, Florent Hivert <florent.hiv...@univ-rouen.fr> wrote: > Hi there, > > I have a slightly stupid question ! First of all consider the following > behavior (sage 4.3.2): > > sage: A = MatrixSpace(ZZ, 3) > sage: A.one() > [1 0 0] > [0 1 0] > [0 0 1] > sage: A.one()[1,2] = 1 > sage: A.one() > [1 0 0] > [0 1 1] > [0 0 1] > > This is definitely bad. It happens because one is generically computed by > coercion from 1 and then cached without making it immutable. I see at least > three solutions: > > 1. - Don't cache at all > 2. - Return a cached immutable
I strongly vote for 2. > 3. - Return a mutable copy of a cached > > To have an idea of the usage I went trough the code: > > - MatrixSpace.identity_matrix implement 1. > - MatrixSpace.zero_matrix implement 3. > > Of course, my opinion is to make those three methods implements 2. :-) +1 > Any arguments in favor one or one other ? I like 2. If you need a copy to mutate, then you can always do A.one().copy(). William > > Cheers, > > Florent > > -- > 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 > -- William Stein Associate Professor of Mathematics University of Washington http://wstein.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
