On Thursday, June 8, 2017 at 5:16:15 PM UTC-7, David Joyner wrote: > > Hi all: > > This is kind of a newbie question, as I'm not an expert on simplicial > complexes. It's also a minor technical issue on the documentation, not > the code. > > I'm trying to debug some code of mine and, on reading the > documentation for chain_complex on > > http://doc.sagemath.org/html/en/reference/homology/sage/homology/simplicial_complex.html, > > > found this: "The rows and columns of the boundary matrices are indexed > by the lists given by the n_cells() method, which by default are > sorted." On the other hand, the documentation for n_cells has this > statement: "Sort the list if the argument sort is True. If sort is > None (the default), then sort depending on the value of the > sort_facets parameter (from the initialization of the simplicial > complex)." However, the sort_facets parameter (unless I'm mistaken) > does not sort the individual faces but rather sorts the vertices in > each facet.
The documentation means that if "sort_facets" was True originally, then n_cells will also sort its result before returning it. ("then sort depending on the value of the sort_facets parameter": so if sort_facets was True, then n_cells should also sort. It doesn't mean "sort using the effect of the sort_facets parameter", but sort depending on its value, which is True or False. This could be made clearer, I guess.) I don't know if there is ever a good reason to specify sort_facets=False. Maybe we should deprecate it? > In my code, I expected the faces of a fixed dimension to > be returned as a deterministic sorted list not a set whose ordering > could be random. Now, it *does* seem as though the faces are sorted. > It's just that, to me, the documentation of n_cells doesn't make that > clear. > > I'm asking if I'm mis-understanding something here or not. > > - David Joyner > -- John -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To post to this group, send email to sage-support@googlegroups.com. Visit this group at https://groups.google.com/group/sage-support. For more options, visit https://groups.google.com/d/optout.