# How do I add 0 after every value in a vektor

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Luqas Lundahl il 25 Feb 2022
Commentato: Luqas Lundahl il 25 Feb 2022
So i have to add 0 after every value in a vektor. The vektor is decided by the user and im trying to use 'for' in the solution.
for example if my vektor is v=[3,5,2,7] the new vektor should be u=[3,0,5,0,2,0,7,0]
what ive come up with so far, i don't know how to use the 'for' command and im trying to learn
u=zeros(1,2*length(v));
for
????
????
end
disp(['The new vektor is [' num2str(u) ']'])
so far i tried replacing the ?? with
n=1:2:length(v);
v(n)=u;
but got the error msg "Unable to perform assignment because the left and right sides have a different number of elements."
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Walter Roberson il 25 Feb 2022
Hint:
v(1) gets written to u(1)
v(2) gets written to u(3)
v(3) gets written to u(5)
so each increment by 1 in the index of v, results in an increment by 2 in the index of u
u(2*n + something) = v(n)

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### Risposta accettata

Image Analyst il 25 Feb 2022
Try this:
v=[3,5,2,7];
for k = 1 : length(v)
index = (k-1) * 2 + 1;
u(index) = v(k);
end
u(end+1) = 0 % Show in command window.
u = 1×8
3 0 5 0 2 0 7 0
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Luqas Lundahl il 25 Feb 2022
That worked! Thank you so much!

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### Più risposte (1)

Jan il 25 Feb 2022
This works without a loop.
v = [3,5,2,7];
Now append a 2nd row with zeros:
v = [v; zeros(size(v))];
% Or equivalently:
v(2, :) = 0;
Remember, that Matlab stores values of arrays in column order. Then:
v(:)
is almost what you want to get. Just transpose it.
Alternative is to create a vectore of zeros in the wanted length:
w = zeros(1, numel(v) * 2);
Now fill the indices 1:2:numel(w) with the elements of v. There is no need for a loop and your "n=1:2:length(v); v(n)=u;" is almost correct.
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Luqas Lundahl il 25 Feb 2022
Thanks you for the answer! However, I'm specifically using 'for' because i want to learn how it works so i can use it more efficiently in the future, so i want my code to include it! If you can help me i would really appriciate it!

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