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

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Jonas Morgner 2022 年 5 月 8 日
コメント済み: VBBV 2022 年 5 月 8 日
% 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?

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### 採用された回答

VBBV 2022 年 5 月 8 日
% 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
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VBBV 2022 年 5 月 8 日
You can simply use
D = d; % With out using loop
for K = 1 : size(d,1)
D(K,1) = d(K); % using loop
end

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