Add certificate option to has_minor

[tara]

Add an option to the "has_minor" method of matroids to return a witness in case a minor is found.

[tara]

New commits:

​ca19af1

Added the option to get the sets `X` and `Y`, where `N` is `M/X\Y`.

[yomcat]

• Line 88 of matroid.pyx has been messed up
• At line 1110, you're missing an enter.
• Line 3893 has bonus whitespace.
• As on the is_isomorphic() ticket, you should explicitly call the option in the doctests.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​85a6317

Fixed errors

[yomcat]

Almost done (I feel like a grumpy old man...)

You've got repeated doctests now.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​6fc388d

Removed repeated doctest

[Stefan]

Should this ticket be in "needs review"?

[Stefan]

Documentation needs to be in standard form. So

    - ``certificate`` -- (default: ``False``) If true, blablabla

The double backquotes are for code variables, the single backquotes are for math. Also note the way defaults are reported.

Documentation can be previewed by running

make doc

and then inspecting (starting from your base Sage directory)

local/share/doc/sage/html/en/reference/matroids/index.html

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​1a33e63

Eddited documentation

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​19826d1

Eddited errors in documentation

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​0b86a6b	Eddited documentation
​d05d6d2	Fixed error in documentation

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​15131de

Fixed spacing error

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​8753305

Fixed doctest

[vdelecroix]

Each ticket needs a proper description (at least a line saying what is the goal). For example, there is no way to guess that all this is about matroids!!

[Stefan]

In the clause 'if N is self' you should still return the tuple (X,Y,dic), where X = Y = frozenset() and dic = {x: x for x in self.groundset()}

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​e8c5b4e

Fixed return when we test if a matroid has itself as a minor.

[Stefan]

I'm happy now