how can i reshape an indexed vector

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fadams18
fadams18 2020-11-2
评论： fadams18 2020-11-2
Hello,
I have the following problem:
Q % e.g. 300 x 300 matrix
M % e.g. 300 x 300 matrix
omega=find(Q); % omega becomes a 86567x1 vector
b= M(omega);% b is also a 86567x1 vector
Is there a way to reshape b to have the same dimension as Q?

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Ameer Hamza
Ameer Hamza 2020-11-2
编辑：Ameer Hamza 2020-11-2
Q has 90000 elements, whereas b has 86567 elements. Direct reshaping is not possible. I guess you are trying to do something like this
Q % e.g. 300 x 300 matrix
M % e.g. 300 x 300 matrix
b = M.*Q
It an element in Q is zero, then it will multiply the corresponding element in M with 0 too.
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Ameer Hamza
Ameer Hamza 2020-11-2
Ok, In that case, you can do something like this
Q = randi([0 1], 300); % e.g. 300 x 300 matrix
M = rand(300); % e.g. 300 x 300 matrix
omega=find(Q); % omega becomes a 86567x1 vector
b = M(omega);% b is also a 86567x1 vector
% apply your algorithm on b vector
B = zeros(size(Q));
B(Q~=0) = b;
B has same size as Q.
fadams18
fadams18 2020-11-2
Thanks a lot man. I guess its my algorithm that has issues. your fix makes sense. only i didnt get the desired image i wanted. Thanks all the same.

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KSSV
KSSV 2020-11-2
Whn you use find you will get the global indices in the form of column array...YOu can use logical indexing, so that you can have your matrix dimensions intact with 1 where condition is obeyed and 0 where condition is not.
omega = Q~=0;
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fadams18
fadams18 2020-11-2
This could be useful in future. Now i understand how the find works. thanks!

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