Re: Combinations
- To: mathgroup at smc.vnet.net
- Subject: [mg30787] Re: [mg30769] Combinations
- From: "Michael" <michael at science.edu>
- Date: Wed, 19 Sep 2001 00:16:26 -0400 (EDT)
- References: <200109100043.UAA00680@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
> Hello. I have Mathematica 4.1 > > In a Program like Excel, or a hand-held calculator, one can return the > number of combinations and permutations. > > However, I can not find an equivalent function in Mathematica. > For example, Permutations[ ] returns a long list of all the "Actual" > permutations. > I am looking for just the final number. > If there is one, could you include 'how' you found it. I have looked > everywhere. > I know DiscreteMath`Combinatorica` has some stuff in it, but the Help system > appears not to explain many of them. > > I can write a custom function, but I am curious to find out if this function > is built in to Mathematica. > > I hope the answer is not to take the Length[ ] of a rather long list. > > TIA. Dana > > (I posted this question a month ago, but it never showed up in the > newsgroup, or in the archives. > I hope I am not doing something wrong.) > The number of permutations is simply Factorial[n] (n!). A quick double-check can be obtained by calling following function with small integers to see if you always get True: verifyP[x_Integer] := Length[Permutations[Range[x]]] == x! If you want to see how many ways you can take a subset of n items out of a total of m items, you can use the Binomial function. For example, how many different ways can you choose 5 objects from 49? In[26]:= Binomial[49, 5] Out[26]= 1906884 Hope this helps. Michael
- References:
- Combinations
- From: "Dana" <ng_only@hotmail.com>
- Combinations