how can i reshape an indexed vector

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fadams18 2020-11-2

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评论： fadams18 2020-11-2

采纳的回答： Ameer Hamza

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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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Answer 1

Ameer Hamza 2020-11-2

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编辑：Ameer Hamza 2020-11-2

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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 2020-11-2

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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 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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Answer 2

KSSV 2020-11-2

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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;