sustaining_gazes/matlab_version/CCNF/CalcSigmaCCNFflat.m

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2016-04-28 19:40:36 +00:00
function [ SigmaInv] = CalcSigmaCCNFflat(alphas, betas, n, precalcQ2withoutBeta, precalc_eye, precalc_zeros)
%CALCSIGMAPRF Summary of this function goes here
% Detailed explanation goes here
% constructing the sigma
% A = zeros(n);
%
% for i=1:n
%
% A(i,i) = alphas' * mask(i,:)';
%
% end
% this is simplification of above code
% if(useIndicators)
% A = diag(mask * alphas);
% else
% A = sum(alphas) .* eye(n);
A = sum(alphas) .* precalc_eye;
% A = sum(alphas) * eye(n);
% not faster
% a = mtimesx(sum(alphas), eye(n), 'SPEED');
% a2 = mtimesx(sum(alphas), eye(n), 'SPEEDOMP');
% end
% calculating the B from the paper
% for i=1:n
% for j=1:n
%
% if(i == j)
% q2(i,j) = beta * (sum(S(i,:)) - S(i,i));
% else
% q2(i,j) = -beta * S(i,j);
% end
% end
% end
% the above code can be simplified by the following lines of code
% using the precalculated lower triangular elements of B without beta
Btmp = precalcQ2withoutBeta * betas;
% not faster
% Btmp = mtimesx(precalcQ2withoutBeta, betas, 'SPEED');
% Btmp = mtimesx(precalcQ2withoutBeta, betas, 'SPEEDOMP');
% now make it into a square symmetric matrix
% B = zeros(n,n);
B = precalc_zeros;
on = tril(true(n,n));
B(on) = Btmp;
B = B';
B(on) = Btmp;
SigmaInv = 2 * (A + B);
end