How can I store the whole diagonal and not only the first element (For loop)

% Part 3.1: Diagonal 
%A
rng('default')
r2 = randi(100,3,3); % Creating a 3x3 matrix, with random values from 1 to 100

%B
d = diag(r2) % Obtain the diagonal elements 


%C
Metod1 = d(2,1) % Using two parameters (row 2, column 1)
Metod2 = d(3) % Using one parametr (3rd element)

%D
for K = 1 : size(d,1)
    d(K,K)
end

I have a problem in storing the diagonal values of the Matrix. It somehow only stores the first entry of the diagonal, where instead it should store 3 entries in total. How can I change the for loop so it also stores the rest of the entries?

Also I get this error message when using the for loop:

"Index in position 2 exceeds array bounds. Index must not exceed 1"

What does it mean and how can I fix this?

Answer 1

[VBBV]

% Part 3.1: Diagonal 
%A
rng('default')
r2 = randi(100,3,3); % Creating a 3x3 matrix, with random values from 1 to 100

%B
d = diag(r2) % Obtain the diagonal elements 

d = 3×1

82 64 96

%C
Metod1 = d(2,1) % Using two parameters (row 2, column 1)

Metod1 = 64

Metod2 = d(3) % Using one parametr (3rd element)

Metod2 = 96

 
%D
for K = 1 : size(d,1)
    D(K,K) = d(K); % d matrix has only 3 rows , 1 col   
end
D   % declare/assign a new matrix which stores all elements of d into D diagonally. 

D = 3×3

82 0 0 0 64 0 0 0 96

[Jonas Morgner]

Awesome Thank you very much! Unfortunately, I forgot to add that I need to store it in a 1x3 or 3x1 vector. How would the code differ if I want to store it in this specific new vector?

[VBBV]

You can simply use

D = d; % With out using loop
for K = 1 : size(d,1)
  D(K,1) = d(K); % using loop 
end