Re: A Question about Combinatorica

*To*: mathgroup at smc.vnet.net*Subject*: [mg102722] Re: [mg102714] A Question about Combinatorica*From*: Tomas Garza <tgarza10 at msn.com>*Date*: Sat, 22 Aug 2009 03:36:11 -0400 (EDT)*References*: <200908210842.EAA13961@smc.vnet.net>

The first question you must ask the author of the book you mention. Number of combinations of n objects taken in sets of k, is that what you mean? The answer to that is n!/k! (n-k)! The actual combinations carry in Mathematica the strange name of KSubsets, and in order to calculate them you must FIRST call the Combinatorica package: thus In[1]:= <<Combinatorica` In[2]:= KSubsets[{"A","B","C","D"},3] Out[2]= {{A,B,C},{A,B,D},{A,C,D},{B,C,D}} Tomas Garza > Date: Fri, 21 Aug 2009 04:42:27 -0400 > From: m.a.elwahaab at gmail.com > Subject: [mg102714] A Question about Combinatorica > To: mathgroup at smc.vnet.net > > Dear Sir, > > I have a question about Combinatorics. > > If we have four different letters as A, B, C, D . > > A text book mentions that Q(4,4)/2 = 3 different combinations. What the > meaning of Q & why division by 2 ? > > How can I do this by Mathematica with combinatorica package? > > I need really for your advice > > Thanks too much > > *Marwa Ali Abd El Wahaab* > *Teaching Assistant * > Faculty of Engineering > Mansoura University > >

**References**:**A Question about Combinatorica***From:*Marwa Abd El-Wahaab <m.a.elwahaab@gmail.com>