Search All of the Math Forum:
Views expressed in these public forums are not endorsed by
NCTM or The Math Forum.


Math Forum
»
Discussions
»
Software
»
comp.softsys.matlab
Notice: We are no longer accepting new posts, but the forums will continue to be readable.
Topic:
Random matrix of 0s and 1s with two not trivial constraints
Replies:
1
Last Post:
Jun 23, 2013 4:54 AM




Random matrix of 0s and 1s with two not trivial constraints
Posted:
Jun 22, 2013 1:17 PM


Hi Guys,
I need to generate a random matrix of K columns and N rows containing 0 and 1 such that
a) each row contains exactly k ones b) each row is different from the other (combinatorics imposes that if N > nchoosek(K,k) there will be nchoosek(K,k) rows)
Assume I want N=10000 (out of all the possible nchoosek(K,k)=27405 combinations) different 1 x K (with K=30), vectors containing k (with k=4) ones and Kk zeros .
This code
clear all; close N=10000; K=30; k=4; M=randi([0 1],N,K); plot(sum(M,2)) % condition a) not satisfied
does not satisfy neither a) nor b).
This code
clear all; close; N=10000; NN=N; K=30; k=4; tempM=zeros(NN,K); for ii=1:NN ttmodel=tempM(ii,:); ttmodel(randsample(K,k,false))=1; %satisfies condition a) tempM(ii,:)=ttmodel; end Check=bi2de(tempM); %from binary to decimal [tresh1,ind,tresh2] = unique(Check);%drop the vectors that appear more than once in the matrix M=tempM(ind,:); %and satisfies condition b)
plot(sum(M,2)) %verify that condition a) is satisfied %Effective draws, Wanted draws, Number of possible combinations to draw from [sum(sum(M,2)==k) N nchoosek(K,k) ]
satisfies condition a) and partially condition b) I say partially because unless NN>>N the final matrix will contain less than N rows each different from each other
Is there a better and faster way (that possible avoids the for cycle and the need of having NN>>N) to solve the problem?
Thanks a lot,
Antonio



