Re: random matrix initialisation...
- To: mathgroup at smc.vnet.net
- Subject: [mg37613] Re: random matrix initialisation...
- From: Mark Westwood <MarkCWestwood at compuserve.com>
- Date: Wed, 6 Nov 2002 06:54:52 -0500 (EST)
- References: <aq86gt$e4j$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Manuel
This is my first go, for an m x m matrix, with n 1s
i) load Combinatorica, we'll need it in a step or two:
<< DiscreteMath`Combinatorica`
ii) create a list with n 1s followed by (m * m)- n 0s:
list = Join[Table[1, {n}], Table[0, {m m - n}]
iii) Create a random permutation of this list, using the Combinatorica
function RandomPermutation:
randomList = RandomPermutation[list]
iv) now partition the list into m rows each of m elements:
randomMatrix = Partition[randomList, m]
v) putting it all together:
x[m_, n_] :=
Partition[RandomPermutation[Join[Table[1, {n}], Table[0, {m m - n}]]],
m]
I think this answers your question.
Regards
Mark Westwood
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!
>
> thanks a lot
>
> m
>
> --