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Make outer normal fans readily available #27993
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Branch: u/nailuj/normalfan_outer |
Commit: |
comment:3
Sage 8.8 is to be released fairly soon so unless this is a blocker this should be moved to the next release. |
comment:4
I don't care much about adding |
comment:5
Replying to @novoselt:
+1 I would leave the default as it is and add the |
comment:6
Actually, I think now it would be better to allow quick "direction flip" either on the polytope or the fan, i.e. make them support |
comment:7
Replying to @novoselt:
This seems to already be possible for
Or you have something else in mind? Yes, I would use |
comment:8
That's exactly what I meant. I think those who care about directions are likely to read the documentation and discover that these are inner normals. After that, if this is not the desired choice for the user, |
comment:9
Replying to @novoselt:
I believe that the proposed change would be in the method That said, I would change the description of the ticket as follows:
Above I would keep the current default.
This is good to me. Further, I would suggest to add
in the documentation of |
Branch pushed to git repo; I updated commit sha1. New commits:
|
comment:12
Replying to @jplab:
Yes. I stumbled upon this inner-outer issue through
Done.
Done. |
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Reviewer: Jean-Philippe Labbé |
Changed keywords from NormalFan, polytope to NormalFan, polytope, days100 |
comment:13
sage: outer_nf = p.normal_fan(direction='blabla')
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comment:15
Replying to @jplab:
I added a 2-d example testing inner, outer, and an invalid direction.
Done.
Done. |
comment:16
Great! Could you do one change: the backtick in the error message should be a single quote. I would also fix the title of the ticket and the description to reflect the actual changes involved. |
Branch pushed to git repo; I updated commit sha1. New commits:
|
comment:18
Replying to @jplab:
Done.
Done. |
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comment:19
The doctest still has backticks. |
Branch pushed to git repo; I updated commit sha1. New commits:
|
comment:21
ok, c'est correct |
Changed reviewer from Jean-Philippe Labbé to Jean-Philippe Labbé, Frédéric Chapoton |
Changed branch from u/nailuj/normalfan_outer to |
For a polytope
P
, bothNormalFan(P)
andP.normal_fan()
return the inner normal fan having the inner facet normals as rays. The outer normal fan, using the outer facet normals, is well-known, but not as easy to find in Sage.As an example, create the polytope on p.193 of Ziegler's "Lectures on Polytopes" with its normal fan:
The result is the inner normal fan of
P
, which is the outer normal fan of-P
.This ticket adds to
Polyhedron.normal_fan
an argumentdirection
set to either'inner'
or'outer'
to determine which of the directions to use. The default will stay'inner'
in order to match the default ofNormalFan
. The description ofNormalFan
is extended by a hint to useNormalFan(-P)
for the outer normal fan.Additionally, this ticket adds in
sage.geometry.polyhedron.representation
a methodInequality.outer_normal
.This allows to obtain the outer normal vector without having to think about the appropriate sign of
Inequality.A()
whenever dealing with the facet inequalities of a polyhedron.CC: @jplab
Component: geometry
Keywords: NormalFan, polytope, days100
Author: Julian Ritter
Branch/Commit:
440689c
Reviewer: Jean-Philippe Labbé, Frédéric Chapoton
Issue created by migration from https://trac.sagemath.org/ticket/27993
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