On Dec 11, 2013, at 8:22 AM, geo909 <[email protected]> wrote:
> Hi all,
>
> From wikipedia:
> In mathematics, in the areas of combinatorics and computer science, a Lyndon
> word is a string that is strictly smaller in lexicographic order than all of
> its rotations. Lyndon words are named after mathematician Roger Lyndon, who
> introduced them in 1954, calling them standard lexicographic sequences
> For example [1,1,2,1,3] is a Lyndon word, but [1,3,1,1,2] is not.
>
> I need to check as efficiently as possible if a given integer sequence is a
> Lyndon word or not. Is there such an option in sage?
> I check the section for Lyndon words in the manual but apparently the only
> way one can check something like that, is in a
> situation like so:
>
> sage: LyndonWord([2,1,2,3])
> Traceback (most recent call last):
> ...
> ValueError: Not a Lyndon word
>
> Is this my only option for checking if something is a Lyndon word? This
> suggests that there is inherently some check in this
> function, but I do not want to use a ValueError for that..
>
> Any advice?
You can use two question marks to see the source code. You can also edit the
source code, so either of the two below should show you what's happening:
LyndonWord??
edit(LyndonWord)
In this case the code of interest is the following:
super(LyndonWord,self).__init__(parent=LyndonWords(),data=data)
if check and not self.is_lyndon():
raise ValueError("Not a Lyndon word")
so it looks like
LyndonWord([2,1,2,3],check=false).is_lyndon()
should do what you want without having to catch a ValueError.
-Ivan
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