how can i reshape an indexed vector

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?

Answer 1

[Ameer Hamza]

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.

[fadams18]

yes but the partiuclar algorithm im using (SVT) doesnt allow this M.*Q form. it wants a vector of the form b= M(omega). So after running the algorithm. I just want to reconstruct image.

[Ameer Hamza]

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]

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.

Answer 2

[KSSV]

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;

[fadams18]

This could be useful in future. Now i understand how the find works. thanks!