CODEWITHSUNDEEP
matlabsvd
Hitmanpaddy
Hitmanpaddy

Reputation: 29

Singular Values Decomposition Matlab

I am researching the above topic and attempting to play about with SVD code in Matlab. I was wondering can anyone explain what the following line of code does?

Sh(logical(eye(size(Sh)))) = Sh_diag;

I can understand the rest, it's just this line of code that is puzzling me. I have tried running in debugger but still can't understand it! I believe eye returns an identity matrix and logical converts Sh to be 1 and 0's?? But I cant figure out how they work together, especially with size of Sh? Thank you in advance.

%Apply SVD to img1
[Uh Sh Vh] = svd(img1);

% Apply SVD to img2
[Uw Sw Vw] = svd(img2);

% Replace singular values of the img1 with the
% singular values of the img2
Sh_diag = diag(Sh);
Sw_diag = diag(Sw);


if (length(img2) >= 256)
    Sh_diag(1:length(Sh), :) = Sw_diag(1:length(Sh), :);
elseif(length(hidden_img) < 256)
    Sh_diag(1:length(img2), :) = Sw_diag(1:length(img2), :);
end
Sh(logical(eye(size(Sh)))) = Sh_diag;%%%????%%

Upvotes: 1

Views: 359

Answers (1)

Alex A.
Alex A.

Reputation: 5586

size(Sh) returns the dimensions of the matrix Sh.

eye(size(Sh)) creates an identity matrix with the same dimensions as Sh.

logical(eye(size(Sh))) converts the elements of the identity matrix to logical values.

Sh(...) is selecting a submatrix of Sh using logical indexing. Here it looks like it's just getting the diagonal elements of Sh.

Sh(...) = Sh_diag is replacing the aforementioned submatrix with Sh_diag.

So in all, this is selecting the diagonal elements of Sh and replacing them with the values in Sh_diag.

Upvotes: 3

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