Thanks to all. The machine is still up, as I was able to stop the computation with Crtl-C.
Now I see it, of course that's what V.sum(W) says that it does, except that it in fact makes no sense, since adding up the (infinitely many) elements of W has nothing to do with V. I don't quite know how I missed V+W -- thanks, David! John On 8 November 2012 10:38, P Purkayastha <ppu...@gmail.com> wrote: > On 11/08/2012 05:36 PM, John Cremona wrote: >> >> Either I am doing something wrong or a simple operation which should >> be fast is in fact very slow, but I do not know why. >> >> If V,W are vector spaces over QQ, subspaces of the same ambient >> space, then V.sum(W) should return their sum, with an echelon basis >> obtained from the bases of V and W. But this takes a stupidly long >> time. For example: >> >> sage: Q100=QQ^100 >> sage: V=Q100.subspace([Q100.random_element()]) >> sage: W=Q100.subspace([Q100.random_element()]) >> >> # so V,W are both 1-dimensional >> >> sage: V.sum(W) >> sage: time V.sum(W) >> >> # takes forever (on 5.3) -- why? >> >> John >> > > What Francis said is correct. V.sum(W) sums the elements in W. Over QQ, the > number of elements is not finite. I am surprised if your machine is still > up, because it should have just exhausted all memory! :) > > > -- > You received this message because you are subscribed to the Google Groups > "sage-devel" group. > To post to this group, send email to sage-devel@googlegroups.com. > To unsubscribe from this group, send email to > sage-devel+unsubscr...@googlegroups.com. > Visit this group at http://groups.google.com/group/sage-devel?hl=en. > > -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To post to this group, send email to sage-devel@googlegroups.com. To unsubscribe from this group, send email to sage-devel+unsubscr...@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel?hl=en.
