# Loop does not save intermediary steps

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Radu Mihail on 31 Dec 2020
Commented: Radu Mihail on 31 Dec 2020
I have a huge matrix A(1540,1540)
I am trying to get all its diagonals under the main one at 3n+1 steps in separate vectors x or strings using the following loop. They all get displayed in my command window but in the Workspace at x I get only the last one(it overwrites the intermediary steps) I am doing something silly
the code
for i = 4:3:size( A,2 )
x=diag(A,-i)'
fprintf('%d', x);
end

Stephen23 on 31 Dec 2020
Edited: Stephen23 on 31 Dec 2020
"Loop does not save intermediary steps"
because nothing in your code makes any attempt to save them. Because each diagonal has a different number of elements, probably the simplest storage is to use a cell array:
A = rand(1540,1540);
V = 4:3:size(A,2);
N = numel(V);
C = cell(1,N);
for k = 1:N
C{k} = diag(A,-V(k));
end
All of the diagonals will be in the cell array C:
For example, the 512th diagonal:
V(512)
ans = 1537
C{512}
ans = 3×1
0.5061 0.4939 0.9809
Basic concepts, like how to save data during a loop, are explained in the starting tutorials:
Radu Mihail on 31 Dec 2020
No words to thank you Stephen! Happy New Year

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