Sparse matrix with determined number of zeros
in [Matlab]
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From: haithem on 23 Jun 2010 00:06 Hi, all. My problem is that I want to generate a sparse vector with a fixed number of non zero elements randomly distributed. Thanks for all
From: Bruno Luong on 23 Jun 2010 03:03 haithem <haithem.haggui(a)gmail.com> wrote in message <ae397350-a6bc-4935-8d00-3beb656223b0(a)g19g2000yqc.googlegroups.com>... > Hi, all. > > My problem is that I want to generate a sparse vector with a fixed > number of non zero elements randomly distributed. A quick and dirty way, this works OK with the density is low. I'm sure there is a better way, but probably requires a lot of code. m=10; n=10; nz=50; S = sparse([],[],[],m,n); a = nz - nnz(S); while a>0 i = ceil(m*rand(1,a)); j = ceil(m*rand(1,a)); S = S + sparse(i,j,1,m,n); a = nz - nnz(S); end Bruno
From: John D'Errico on 23 Jun 2010 05:19 "Bruno Luong" <b.luong(a)fogale.findmycountry> wrote in message <hvsbjp$q6u$1(a)fred.mathworks.com>... > haithem <haithem.haggui(a)gmail.com> wrote in message <ae397350-a6bc-4935-8d00-3beb656223b0(a)g19g2000yqc.googlegroups.com>... > > Hi, all. > > > > My problem is that I want to generate a sparse vector with a fixed > > number of non zero elements randomly distributed. > > A quick and dirty way, this works OK with the density is low. I'm sure there is a better way, but probably requires a lot of code. > > m=10; > n=10; > nz=50; > > S = sparse([],[],[],m,n); > a = nz - nnz(S); > while a>0 > i = ceil(m*rand(1,a)); > j = ceil(m*rand(1,a)); > S = S + sparse(i,j,1,m,n); > a = nz - nnz(S); > end > > Bruno I would probably use sprand to randomly generate a sparse matrix with say 10% more zeros on average than your goal. Then find the non-zeros, and delete (at random) exactly the number needed to give your target number of non-zeros. Other ways exist, but they will take more work than is worth expending here. John
From: us on 23 Jun 2010 06:28 haithem <haithem.haggui(a)gmail.com> wrote in message <ae397350-a6bc-4935-8d00-3beb656223b0(a)g19g2000yqc.googlegroups.com>... > Hi, all. > > My problem is that I want to generate a sparse vector with a fixed > number of non zero elements randomly distributed. > > Thanks for all one of the many (other) solutions n=10; nr=2; s=spalloc(1,10,10); rp=randperm(n); s(rp(1:nr))=1; us
From: Bruno Luong on 23 Jun 2010 06:37
"us " <us(a)neurol.unizh.ch> wrote in message <hvsnjk$1ju$1(a)fred.mathworks.com>... > haithem <haithem.haggui(a)gmail.com> wrote in message <ae397350-a6bc-4935-8d00-3beb656223b0(a)g19g2000yqc.googlegroups.com>... > > Hi, all. > > > > My problem is that I want to generate a sparse vector with a fixed > > number of non zero elements randomly distributed. > > > > Thanks for all > > one of the many (other) solutions > > n=10; > nr=2; > s=spalloc(1,10,10); > rp=randperm(n); > s(rp(1:nr))=1; > > us The problem is for large sparse matrix size such as m x n = 1e6 x 1e6, generate a randperm of size 1e12 is a no-no. Bruno |