Opened 7 years ago
Closed 6 years ago
#15107 closed enhancement (fixed)
Projective Plane designs
Reported by:  ncohen  Owned by:  

Priority:  major  Milestone:  sage6.1 
Component:  combinatorics  Keywords:  
Cc:  dimpase  Merged in:  
Authors:  Nathann Cohen  Reviewers:  Stefan van Zwam 
Report Upstream:  N/A  Work issues:  
Branch:  u/ncohen/15107 (Commits)  Commit:  6f247f6e7f3f704d30f12af082d3e8a4c2120227 
Dependencies:  Stopgaps: 
Description
Shortcut to another function. In order to save a stranger the time it took me to understand it :P
Nathann
Change History (21)
comment:1 Changed 7 years ago by
 Branch set to u/ncohen/15107
 Status changed from new to needs_review
comment:2 Changed 6 years ago by
 Status changed from needs_review to needs_work
comment:3 followup: ↓ 6 Changed 6 years ago by
 Status changed from needs_work to needs_review
OKayyyyyyy. Branch updated :)
comment:4 Changed 6 years ago by
in ProjectiveGeometryDesign
:
 one does not know what is the input F
 there is a missing :: in the modified example block
comment:5 Changed 6 years ago by
Fixed ! Sorry 'bout that :)
Nathann
comment:6 in reply to: ↑ 3 Changed 6 years ago by
Replying to ncohen:
OKayyyyyyy. Branch updated
:)
the function name is unfortunate; it should reflect the fact that there could be several examples, or, rather, make it unique, like ClassicalProjectivePlane
or DesarguesianProjectivePlane
or something like this. Otherwise it would preclude adding code for nonclassical examples.
comment:7 Changed 6 years ago by
Well, I see a ProjectivePlane
method as one that will give me "some projective plane", and I can't make more assumptions on what it is. I would also like someone who just wants "a projective plane" to be able to find the method, for I need projective planes and I have no idea what a Desarguesian projective plane is, nor if the one I implemented is classical.
Plus I implemented a steiner_triple_system
method which returns only one kind of steiner triple systems, I did the same for steiner_quadruple_systems
, ... :P
What would you think of this : we keep ProjectivePlaneDesign
as the method name for the moment, and if we end up with more data we will just make it accessible visible in the doc ?
Combinatstyle, this thing should be a new ProjectivePlanes
class with an an_element
method to return some projective plane, and none other. But we can't even write a .cardinality()
method, nor enumerate them... :P
And if you insist I will rename this to ClassicalProjectivePlaneDesign
.
Have fuuuuuuuuuuuuuuuuuuuuuuuun ! ;)
Nathann
comment:8 Changed 6 years ago by
http://en.wikipedia.org/wiki/Desargues%27_theorem is a geometric criterion satisfied by projective planes obtained from the 3dimensional vector spaces over division rings; every finite division ring is a field, so in the finite case every such plane is Pappian, see http://en.wikipedia.org/wiki/Pappus%27s_hexagon_theorem.
Keeping the current name sucks, as adding more examples would force you to rename stuff. So, please, call it, as you prefer: Classical, or Pappian, or Desarguesian...
As far as ProjectivePlanes
class would go, you can do cardinality()
up to n=10...
comment:9 Changed 6 years ago by
 Commit set to 9fcfb13f3c62e9f8a759063cf86d629b13db754f
Branch pushed to git repo; I updated commit sha1. New commits:
[changeset:9fcfb13]  Rename the method from ProjectivePlaneDesign? to DesarguesianProjectivePlaneDesign? 
[changeset:363badb]  trac 15107  reviewer's comments 
[changeset:ee6d412]  Projective Plane designs constructor 
comment:10 followup: ↓ 11 Changed 6 years ago by
Cool automatic message O_o
Nathann
comment:11 in reply to: ↑ 10 Changed 6 years ago by
Replying to ncohen:
Cool automatic message
O_o
By git... Perhaps the sage git dev scripts should get a better, more descriptive, name... Shlimazl, maybe :)
comment:12 Changed 6 years ago by
 Commit changed from 9fcfb13f3c62e9f8a759063cf86d629b13db754f to cf71d58dedd357692ea90749090adee9ffadd629
Branch pushed to git repo; I updated commit sha1. New commits:
[changeset:cf71d58]  Rebase on 5.13.beta0 
comment:13 Changed 6 years ago by
Sorry Nathann, but what is exactly the purpose of the newfunction DesarguesianProjectivePlaneDesign
?
In my opinion, with this name, it does no longer make sense to answer 'No projective plane design of order 10 exists' or 'If such a projective plane exists, we do not know how to build it.' One should rather check if the input is a prime power and that's it.
Then it would be just a restriction of ProjectiveGeometryDesign? to the dimension 2, i.e. some kind of alias. Either this is considered not useful, and this ticket can be forgotten, or you want to keep it as an useful alias, and it will be ok.
comment:14 Changed 6 years ago by
Helloooooo !
Well, the purpose of this function is to return a projective plane design, i.e. a d^2+d+1, d+1
BIBD.
I agree with what you said. Actually, thinking about it again, I don't agree with what Dima said above. I don't see the problem with calling this ProjectivePlaneDesign
, as I need a function which returns a projective plane design. Changing the name just makes it harder to find when one looks for it >_<
What do you think ?
I think that this alias is useful, but I personally spent quite some time trying to figure out of to obtain a projective plane design with Sage.
Nathann
comment:15 Changed 6 years ago by
 Commit changed from cf71d58dedd357692ea90749090adee9ffadd629 to b6aa35a203041a0ccea849bb8157cff80002b428
comment:16 Changed 6 years ago by
I just updated this ticket after the englightening discussion held on sagedevel : https://groups.google.com/d/topic/sagedevel/a6I0SUZVgNM/discussion
We now have an additional argument to ProjectivePlaneDesign? which does nothing. That's for the sake of art.
Nathann
comment:17 Changed 6 years ago by
There is a typo "afinite projective plane"
I propose to replace "No other value is available for this parameter." by
"For the moment, no other value is available for this parameter."
comment:18 Changed 6 years ago by
 Commit changed from b6aa35a203041a0ccea849bb8157cff80002b428 to 6f247f6e7f3f704d30f12af082d3e8a4c2120227
Branch pushed to git repo; I updated commit sha1. New commits:
6f247f6  trac #15107: back to the first name with a new argument

e2935fe  Trac #15107: Rebase on 6.1.beta3

cf71d58  Rebase on 5.13.beta0

9fcfb13  Rename the method from ProjectivePlaneDesign to DesarguesianProjectivePlaneDesign

363badb  trac 15107  reviewer's comments

ee6d412  Projective Plane designs constructor

comment:19 Changed 6 years ago by
Here it is ! I updated the last commit :)
Nathann
comment:20 Changed 6 years ago by
 Reviewers set to Stefan van Zwam
 Status changed from needs_review to positive_review
I think this looks fine and is ready to go in.
Just for fun, I did the following additional consistency check:
sage: S = designs.ProjectiveGeometryDesign(2,1,GF(3)) sage: M = Matroid(circuit_closures={2:S.blocks(),3:[range(13)]}) sage: M.is_isomorphic(matroids.PG(2,3)) True
comment:21 Changed 6 years ago by
 Resolution set to fixed
 Status changed from positive_review to closed
Your code returns a very particular projective plane, the one obtained from the finite field of order n, whereas there could be many nonisomorphic ones (the first such case being n=9). This should be reflected in the docs, IMHO.