Re: random matrix initialisation...
- To: mathgroup at smc.vnet.net
- Subject: [mg37616] Re: [mg37576] random matrix initialisation...
- From: Sseziwa Mukasa <mukasa at jeol.com>
- Date: Wed, 6 Nov 2002 06:56:29 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
On Tuesday, November 5, 2002, at 05:01 AM, Manuel Marques-Pita wrote:
>
> hello,
>
> i have a question regarding matrices. searched on the web and forums
> but maybe due to using wrong keywords i am not finding an answer...
>
> i need a way or function X to initialise matrices in mathematica such
> that each time i call X i get a matrix with a predetermined number of
> elements initialised as "1" and the rest as "0"
>
> examples
>
> X(4,3)
>
> {{0,0,0,0}, {0,0,1,0}, {0,0,0,1}, {1,0,0,0}}
>
> again X(4,3)
>
> {{1,1,0,0}, {0,0,0,0}, {0,0,0,0}, {0,1,0,0}}
>
> etc.. (first argument means that the matrix is 4x4 and second means
> that there should be 3 "1's" present in the matrix
>
> any help, pointers, etc will be appreciated!
>
How about:
<< DiscreteMath`Combinatorica`
generateRow[m_,n_,1]:=With[{p=RandomKSubset[m,n]},{Table[If[MemberQ[p,i]
,1,0],{i,m}]}]
generateRow[m_,n_,r_]:=Block[{t=Random[Integer,{0,n}],p},p=RandomKSubset
[m,t];{Table[If[MemberQ[p,i],1,0],{i,m}],Sequence@@generateRow[m,n-t,r-
1]}]
generateRow[m_,n_]:=generateRow[m,n,m]
This should work for small matrices. I suppose you could remove the
recursion by using a Do loop which would allow you to create larger
matrices without worrying about $RecursionLimit.
Regards,
Sseziwa