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Occurences of a certain factor in the Kolakoski word

16 février 2011 | Catégories: Kolakoski, sage | View Comments

The factor 212212112112212112122112112212212112112212112122112112 occurs in the Kolakoski word at the positions 3190, 6366, 7614, 12950, 13765, 14277, 20385, 21344, 39674 and so on. The successive gaps of these first eight occurences are 3176, 1248, 5336, 815, 512, 6108, 959, 18330. Are the gap between all of these occurences bounded or not? The following table lists only the gap that are going increasingly for the Kolakoski word up to 100 billion (=10^9).

i ith occurence (i+1)th occurence gap
0 3190 6366 3176
2 7614 12950 5336
5 14277 20385 6108
7 21344 39674 18330
8 39674 58946 19272
17 85963 107018 21055
225 945732 966924 21192
685 2832810 2858670 25860
822 3549762 3583161 33399
965 4188934 4223349 34415
1526 6773992 6809208 35216
7117 31279355 31320896 41541
18054 79167173 79213333 46160
20838 90761663 90809563 47900
176198 768146935 768195609 48674
292643 1278852293 1278906094 53801
554207 2424441033 2424495471 54438
590128 2581311276 2581367730 56454
948506 4150204101 4150264753 60652
1156072 5055131250 5055199553 68303
1514374 6620302433 6620372047 69614
11154155 48788048239 48788121823 73584

The following image draws all the gaps in function of i for the first 10 million digit.

/Files/2011/kolakoski_from0_to10000000.png
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Writing object oriented code in Python

20 janvier 2011 | Catégories: sage | View Comments

I am currently at Sage Days 28. Right now, there is a discussion about Analytic combinatorics in Sage and the new code written by Alex Raichev at tikcet #10519 was mentionned in the discussion. His code is a bunch of def python functions in a sage file. In Sage, code is written in object oriented way.

I am not an expert of the domain of analytic combinatorics, but I am coding oriented object Python since some time now. So I wrote a comment on the ticket gathering my thoughts to, I hope, help Alex to rewrite his set of functions into an oriented object structure. I copied the content of my comment below as it will be easier to share it.

Writing object oriented code : Finding the objects

How to structure a bunch of functions into classes? How to find which objects (python classes) you need? Here is the trick I personaly use. Consider each of your functions as a question you ask. Then, ask yourself to who are you asking each of your questions? Answers often gives you a good hint about the objects you need to implement. EXAMPLE. Suppose I code the function determinant. Question : To who do I ask the determinant?. Answer: To a matrix. Hence, matrix might be a good object (a python class) to implement.

You are the best person to answer to these questions. You might have 30 functions in your file, but only two or three different answers to the above question. Regroup the similar functions together: they will become the methods of a same class.

The sage file you uploaded starts with:

r"""
[...]

This code relates to analytic combinatorics.
More specifically, it is a collection of functions designed
to compute asymptotics of Maclaurin coefficients of certain classes of
multivariate generating functions.

The main function asymptotics() returns the first `N` terms of
the asymptotic expansion of the Maclaurin coefficients `F_{n\alpha}`
of the multivariate meromorphic function `F=G/H` as `n\to\infty`.
It assumes that `F` is holomorphic in a neighborhood of the origin,
that `H` is a polynomial, and that asymptotics in the direction of
`\alpha` (a tuple of positive integers) are controlled by smooth
or multiple points.

[...]
"""

Reading only these lines, I imagine the following structure:

class HolomorphicMultivariateMeromorphicFunction(object):

    # Constructor of the object
    def __init__(self, F, G):
        #stores important information on the object as attributes of self
        self._F = F
        self._G = G

    def maclaurin_coefficients(self, n, alpha):
        r"""
        Return the maclaurin coefficients of self.

        INPUT:

        - ``alpha`` - tuple of positive integers

        OUTPUT:

        a python list of the first terms

        OR

        maybe an object of a class you implement if there exists pertinent
        questions to ask to it.
        """
        #Do some computations based (I guess) on self._F and self._G
        intermediate_result1 = self.some_intermediate_computations_1()
        #Do more computations
        return something

    def asymptotics(self, N, alpha):
        r"""
        Returns the asymptotics of Maclaurin coefficients.
        """
        #Do some computations based (I guess) on self._F and self._G
        intermediate_result2 = self.some_intermediate_computations_2()
        intermediate_result3 = self.some_intermediate_computations_3()
        return something

    #put here all the others functions needed to compute the asymptotics
    def some_intermediate_computations_1(self):
        pass
    def some_intermediate_computations_2(self):
        pass
    def some_intermediate_computations_3(self):
        pass

    ...

It also looks like you need some robustness somehow. But I need to know more information about what means

"that asymptotics in the direction of \(\alpha\) (a tuple of positive integers) are controlled by smooth or multiple points."

to decide whether this is checked at the creation of the object or before returning the asymptotics. But these hypothesis should be checked somewhere.

Hope this helps.

Cheers,

Sébastien Labbé, Montréal, (but currently at Sage Days 28, Orsay, France)

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How to contribute to Sage talk at Sage Days 28

19 janvier 2011 | Catégories: sage | View Comments

At Sage Days 28 held this week in Orsay, France, I gave a talk on How to contribute to Sage.

The talk goes into the details because we wanted people to contribute during the talk. Tickets created during the talk are here :

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Sharing my branch of Sage development

19 novembre 2010 | Catégories: sage | View Comments

The purpose of this text also available on the Sage wiki is to explain how to share your branch of Sage development. I am sure there more than one way to do so, but the solution shown here is the same as the way Sage Combinat shares its development.

First, clone the sage-main. Below, I use my sage trac username to name that branch, because it's my branch of Sage development:

sage -b main
sage -clone slabbe

Go to the directory associated to that new branch and initialize the Queue for Mercurial. See Sage Development Manual : Mercurial queues for more details.

cd SAGE_HOME/devel/sage-slabbe
hg qinit

This last step created a new directory (SAGE_HOME/devel/sage-slabbe/.hg/patches) where your patches will be saved. In order to share your branch, you simply need to share this directory. For example, you can copy its content to a public directory on your web site. You can also use svn, git or any other revision control system. As I want to work on my branch the exact same way as I am working on the sage-combinat branch, I choose to use hg.

Now I log on the server that will host my patches, I create the (public) patches directory and I initialize that directory as an hg directory:

ssh username@server.com
mkdir patches
cd patches
hg init

I also add a hook to that public repository so that it updates itself automatically when a push is made to it. In other words, I edit the file ~/patches/.hg/hgrc so that it becomes:

#file ~/patches/.hg/hgrc
[hooks]
changegroup = hg update

I then logout from the server and go to the patches directory on my machine and make a clone of the public patches repository created above. I could use the http adress, but I use the ssh one so that I can push to the server later on:

cd SAGE_HOME/devel/sage-slabbe/.hg/patches
hg clone ssh://username@server.com:~/patches .

Like for the Sage-combinat repository, I create in .hg/patches a file called .hgignore containing the following:

# file .hgignore
syntax: glob
status
guards

Then, add, commit and push this first change to the server:

hg add .hgignore
hg commit -m "Added the .hgignore file"
hg push

I can now create patches on my branch like in sage-combinat:

cd SAGE_HOME/devel/sage-slabbe/
hg qnew trac_XXXX-fixing-stuff.patch
vim sage/combinat/partition.py
hg qrefresh -e

I can push my changes to my public server like in sage-combinat:

cd SAGE_HOME/devel/sage-slabbe/.hg/patches
hg st
hg commit
hg push

For the first time, you may need to add the series file as well:

cd SAGE_HOME/devel/sage-slabbe/.hg/patches
hg add series
hg commit
hg push

Last thing, notice that the sage-combinat script can be used to install your branch on any Sage installation with the following one liner:

sage -combinat install -b slabbe -s http://server.com/path/to/your/username/patches/

In my case, the result is here

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Le ruissellement pour préserver l'équilibre démocratique de la FQU

13 novembre 2010 | Catégories: ultimate, fqu | View Comments

Le ministère de l'éducation des loisirs et du sports du Québec demande de modifier les règlements généraux de la Fédération québécoise d'ultimate afin d'éviter qu'une association ait un droit de veto sur les votes faits à double majorité.

À ce problème, je propose la solution suivante que j'ai appelé principe du ruissellement:

Explication brève:

Le ruissellement est une répartition du poids des associations pour les votes à double majorité qui s'applique lorsqu'une association est majoritaire, c'est-à-dire possède plus de 50 pour cent des membres individuels de la FQU. Le ruissellement consiste à modifier le poids de l'association majoritaire à 49 pour cent et répartir l'éxédent du 49 pour cent aux autres associations en commençant par l'association la plus petite en nombre de membres et jusqu'à ce que le poids de cette association égalise celui de la deuxième association, puis aux deux associations les plus petites jusqu'à ce qu'elles égalisent le poids de la troisième, puis aux trois associations les plus petites jusqu'à ce qu'elles égalisent le poids de la quatrième, et ainsi de suite jusqu'à épuisement de l'exédent.
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