rickhg12hs wrote: > On Jun 20, 10:18 pm, Robert Bradshaw <rober...@math.washington.edu> > wrote: >> sage: n = 10 >> sage: m = block_matrix([0, zero_matrix(1,1), identity_matrix(n), 0]) >> sage: m.subdivide() # get rid of the block divisions >> sage: m >> [0 0 0 0 0 0 0 0 0 0 0] >> [1 0 0 0 0 0 0 0 0 0 0] >> [0 1 0 0 0 0 0 0 0 0 0] >> [0 0 1 0 0 0 0 0 0 0 0] >> [0 0 0 1 0 0 0 0 0 0 0] >> [0 0 0 0 1 0 0 0 0 0 0] >> [0 0 0 0 0 1 0 0 0 0 0] >> [0 0 0 0 0 0 1 0 0 0 0] >> [0 0 0 0 0 0 0 1 0 0 0] >> [0 0 0 0 0 0 0 0 1 0 0] >> [0 0 0 0 0 0 0 0 0 1 0] >> >> You can also use this to get anything you want on the sub-diagonal >> (or pretty much anywhere). >> >> sage: m = block_matrix([0, zero_matrix(1,1), diagonal_matrix([10, 20, >> 30, 40]), 0]); m.subdivide(); m >> [ 0 0 0 0 0] >> [10 0 0 0 0] >> [ 0 20 0 0 0] >> [ 0 0 30 0 0] >> [ 0 0 0 40 0] > > Very nice - I didn't know about block_matrix. In addition, it seems > block_matrix has an optional argument "subdivide". > > sage: n = 10 > sage: m = block_matrix([0, zero_matrix(1,1), identity_matrix(n), > 0],subdivide=False) > sage: m > [0 0 0 0 0 0 0 0 0 0 0] > [1 0 0 0 0 0 0 0 0 0 0] > [0 1 0 0 0 0 0 0 0 0 0] > [0 0 1 0 0 0 0 0 0 0 0] > [0 0 0 1 0 0 0 0 0 0 0] > [0 0 0 0 1 0 0 0 0 0 0] > [0 0 0 0 0 1 0 0 0 0 0] > [0 0 0 0 0 0 1 0 0 0 0] > [0 0 0 0 0 0 0 1 0 0 0] > [0 0 0 0 0 0 0 0 1 0 0] > [0 0 0 0 0 0 0 0 0 1 0] >
I should mention that these methods are all nice for this problem, but they also end up copying an awful lot of zeros. I think it would be way more efficient in general to make a zero matrix, then set the right diagonal by hand using a for loop. Jason --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
