On Mon, Jun 1, 2009 at 5:16 PM, davidp <dav...@reed.edu> wrote: > > Is there a fast way to create a submatrix? > > ------------------------------------------------- > > > sage: version() > 'Sage Version 4.0.alpha0, Release Date: 2009-05-15' > sage: G = graphs.GridGraph([100,100]) > sage: L = G.laplacian_matrix() > sage: L > 10000 x 10000 sparse matrix over Integer Ring > sage: time M = L[1:9999,1:9999] > CPU times: user 24.93 s, sys: 0.04 s, total: 24.97 s > Wall time: 25.27 s > > > ---------------------------------------------------- > > I am just interested in deleting a single row and column of the matrix > (not necessarily the first). > > Thanks,
There is no fast way to do that right now. One could easily add code to SAGE_ROOT/devel/sage/sage/matrix/matrix_integer_sparse.pyx that would provide blazingly fast deletion of a row, and reasonably fast deletion of a column. Of course it would be better to implement arbitrary slicing in some optimized way in matrix_integer_sparse.pyx. I hope somebody does so. William --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
