0 个投票

Hi everyboy
I am trying to vectorize the following code, but I can't. I want to calculate the matrix p_hat from the matrixs p and omega (these last matrix are of the same order) . The vector a is a function that gives me another index.
Could anyone help me, please?
for k=1:length(a)
for j=1:length(a)
if omega(j,k)==1
p_hat(k,a(j))=p(j,k);
end
end
end

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Stephen23
Stephen23 2018-6-2
" The vector a is a function that gives me another index"
It can't be both: is it a vector, or a function?

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 采纳的回答

Jan
Jan 2018-6-2
编辑：Jan 2018-6-2

0 个投票

Assuming that omega is a logical matrix (please post what the inputs are, such that the readers do not have to guess the details):
p_hat = zeros(length(a), length(a)); % Needed only if p_hat is existing before
p_hat(:, a) = (p .* omega).';
Some assumed test data:
omega = rand(10, 10) > 0.2;
a = randperm(10);
p = rand(10, 10);
p_hat2(:, a) = (p .* omega).'; % Vectorized
p_hat = zeros(length(a), length(a)); % Loop
for k=1:length(a)
for j=1:length(a)
if omega(j,k)==1
p_hat(k,a(j))=p(j,k);
end
end
end
isequal(p_hat, p_hat2) % Compare
>> logical(1)

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Yes, it works. But how to vectorize de outer loop? Maybe something like
p_hat(1:length(a), a_aux(omega(:, 1:length(a)))) = p(omega(:, 1:length(a)), 1:length(a));
Jan
Jan 2018-6-2
See the edited answer.

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Bruno Luong
Bruno Luong 2018-6-2
编辑：Bruno Luong 2018-6-2

1 个投票

p = rand(3,4)
a = ceil(10*rand(size(p,1),1))
omega = rand(size(p))>0.4
[j,k] = find(omega)
p_hat = accumarray([k,a(j)],p(omega))

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