[with patch; positive review] Add support for posets, semi-lattices, etc. to Sage

[saliola]

Initial support for finite posets. (Patch against sage-3.0.)

[saliola]

See announcement and discussion on sage-devel:

 http://groups.google.com/group/sage-devel/browse_thread/thread/b6fcc3a134abe22c

[rlm]

Some comments:

1. Lattice should be LatticePoset or something similar. Same comment for Chain, Antichain, Pentagon and Diamond.

1. This is a great example of good code. The docstrings are generous and everything is well tested. Nice work!

[saliola]

1. Lattice should be LatticePoset or something similar. Same comment for Chain, Antichain, Pentagon and Diamond.

Done. As a remark: we eventually want to create a poset database similar to the graph database. So these poset examples will be moved into the database.

1. This is a great example of good code. The docstrings are generous and everything is well tested. Nice work!

Thank you!

There are a few other differences between the original patch and the new patch:

1. Added "or equal to" to the docstrings for is_gequal and is_lequal.

2. I redefined the show methods for FinitePoset and HasseDiagram. Before it
was just show = plot, but I since realized this is wrong: show should show the
Graphics object returned by the plot method.

3. Added the methods interval, closed_interval and open_interval to the FinitePoset
class. These already existed for the HasseDiagram class; so the new methods
just expose these methods from the FinitePoset class. It was an oversight not
to have done this originally.

4. I slightly modified HasseDiagram.antichains to return the empty list as an
antichain. And added tests.

[rlm]

Regarding show versus plot, you don't even really need a show: most Sage objects give LaTeX when you call show, and if you do sage: P.plot(), the graphics object will appear.

Also, it looks like you need both patches in order, right?

[saliola]

Apply both patches in order!

[saliola]

Replying to rlm:

Regarding show versus plot, you don't even really need a show: most Sage objects give LaTeX when you call show, and if you do sage: P.plot(), the graphics object will appear.

I'll leave it as is, as this is how it is implemented for Graphs/DiGraphs?.

Also, it looks like you need both patches in order, right?

Yes, I patched against the previous patch. I've corrected what I wrote.

I can provide a single patch instead if that is easier.

[rlm]

As long as it applies cleanly and passes all tests...

[mabshoff]

With both patches applied the doctests pass. Two comments:

• sage/combinat/posets/init.py is zero bytes, so the patch doesn't create it. I fixed that manually
• these patches are regular diffs and not mercurial patches, so I ended up with the formal credit when applying them. I did however state in the changelog:

  changeset:   9746:0f14afe7ba00
  tag:         tip
  user:        mabshoff@sage.math.washington.edu
  date:        Thu May 22 16:52:19 2008 -0700
  summary:     Apply patch by Peter Jipsen and Franco Saliola: Add support for posets, semi-lattices, etc
  
  changeset:   9745:0716b13a9e12
  user:        mabshoff@sage.math.washington.edu
  date:        Thu May 22 16:52:08 2008 -0700
  summary:     Apply patch by Peter Jipsen and Franco Saliola: Add support for posets, semi-lattices, etc.
  

Cheers,

Michael

[mabshoff]

Merged in Sage 3.0.2.rc0