
Re: Efficiently computing large numbers of vector norms
Posted:
Nov 13, 2012 2:23 PM


I cannot repeat your test, as I get an "Out of Memory" error. Furthermore, I require that A1 and A2 change on each iteration. Therefore, the KronProd() operation must also go inside the tic/toc.
Perhaps you could copy and paste my code (for which I get comparable performance using a simple loop):
Ntrials = 100;
% Data Dimensions N1 = 9; N2 = 7; Q1 = 180; Q2 = 63;
% Data A1 = randn(N1,Q1) + 1j*randn(N1,Q1); A2 = randn(N2,Q2) + 1j*randn(N2,Q2); X2 = randn(N1*N2,N1*N2) + 1j*randn(N1*N2,N1*N2);
tic Z2b = zeros(Q1,Q2); for trial = 1:Ntrials for j = 1:Q2 Z2b(:,j) = sum(abs(kron(A1,A2(:,j))'*X2).^2,2); end end t = toc; disp(['Single Loop = ',num2str(t), ' secs'])
tic for trial = 1:Ntrials Z2c = reshape(sum(abs(kron(A1,A2)'*X2).^2,2),Q2,Q1).'; end t = toc; disp(['No Loop = ',num2str(t), ' secs'])
tic for trial = 1:Ntrials Z2d = reshape(sum(abs(KronProd({A2',A1'})*X2).^2,2),Q2,Q1).'; end t = toc; disp(['Fast KronProd = ',num2str(t), ' secs'])

