Thread Subject:

program the list of triangles and quadrilateres out of 6000

Hi everybody,
I am trying to compute the list of all triangles and quadrilateres that one can make out of a list i have of more than 6000 vertices (identified with names, in fact these are neurons). I tried on excel, but that's too complicated. I haven't done programming for more than 25 years, so i am looking for an existing program (i have matlab, maple and splus).
Someone can help me?
Thanks in advance,
Cheers,
Florent

"florent.dieterlen@bluewin.ch" <florent.dieterlen@bluewin.ch> wrote in message <31343761.1236706435842.JavaMail.jakarta@nitrogen.mathforum.org>...
> Hi everybody,
> I am trying to compute the list of all triangles and quadrilateres that one can make out of a list i have of more than 6000 vertices (identified with names, in fact these are neurons). I tried on excel, but that's too complicated. I haven't done programming for more than 25 years, so i am looking for an existing program (i have matlab, maple and splus).
> Someone can help me?
> Thanks in advance,
> Cheers,
> Florent

  Matlab's 'nchoosek' function is designed to make such a list. It lists all ways of choosing k elements out of a total of n. I would remind you however that if n is 6000 and k is 4 for your quadrilaterals, the list you generate would have a length of 6000*5999*5998*5997/6 = 5.4e13 which is a very long list indeed.

Roger Stafford

Hi Roger,
In fact, it is a graph, and the number of quadrilateres should be small. I shall try the program you suggest.
Thanks,
Cheers,
Florent