#19552: images and preimages for projective subscheme
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Reporter: bhutz | Owner: bhutz
Type: enhancement | Status: needs_info
Priority: minor | Milestone: sage-6.10
Component: algebraic | Resolution:
geometry | Merged in:
Keywords: subscheme | Reviewers: Vincent Delecroix
iteration | Work issues:
Authors: Ben Hutz | Commit:
Report Upstream: N/A | 5635becc9dd31f1e81c10f5422b37607e3ecdaa3
Branch: | Stopgaps:
u/bhutz/ticket/19552 |
Dependencies: |
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Comment (by bhutz):
1) I will update the docs.
2) hmm..I was matching the inputs that are used for the orbit function for
affine and projective points. I was not aware of the python conventions
covering such a situation. If we follow them here, then the other
functions should be changed to match. This is fine by me, but I'll make
the other function changes in a separate ticket.
3) `orbit` returns a list of points and `nth_iterate` returns a single
point. I use the functions separately as they exists for points, so I
continued the separation here. Combining them would make finding an nth-
iterate slightly more cumbersome: you would have to create the list
`orbit(f,(n,n+1))` and then get the first element out of that list. As I
didn't think there was a significant drawback with making them 2 separate
functions and as a user, I'd rather have two functions.
`forward_image` is used by call and I debated making it private or not. I
think with `nth_iterate` existing, I can make this private.
using `orbit` for preimages is a little shaky in my opinion. The forward
images are single points(or varieties) but the preimages are collections
of points (or varieties). Allowing something like `x.orbit(-2,2)` would
return quite a strange object. So, I see this functionality as different.
In the special case of automorphisms, using `orbit` for both would make
sense, but I don't think it does in general.
--
Ticket URL: <http://trac.sagemath.org/ticket/19552#comment:7>
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