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