MATLAB: How to extract diagonal elements of multiple nxn square matrix and place them in single mat file or matrix

Question

Hello,

I have 500 mat files with 10×10 double dimension. I want to extract the 10 diagonal elements from each matrix and place them in a single matrix which will be 500×10 (500 rows and 10 columns) each row consists of diagonal elements of one matrix. How can I make a single variable with all the diagonal elements?

Thanks

Answer 1

Hope this helps

step1:creat a nXnXm with random elements for the example:

    %set dimensions of matrix 
    size_of_matrix=10;
    number_of_matricides=500;
    mat_input=randi(30,size_of_matrix,size_of_matrix,number_of_matricides);

step2: initialize an output matrix with nXm dimensions

    mat_output=zeros(number_of_matricides,size_of_matrix);

step3: extract a diagonal from each matrix and place them in the output matrix

    for i=1:number_of_matricides
        mat_output(i,:)=diag(mat_input(:,:,i));
    end

Alternatively, though not recommended, you can simply concatenate:

     %initialize an empty matrix
    mat_output=[];
    for i=1:number_of_matricides
       mat_output=[mat_output;diag(mat_input(:,:,i))'];
    end