Multiplying every secound element in a vector with -1

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Hello I am looking for how to multiply every secound element in vector 1xn with -1, but I want to write this as a function. I can do this manually like this for example with an 1x3 vector;
function vny = byt_tecken(v)
vny=[v(1,1),-v(1,2),v(1,3)]
end
But how do I do this for any given 1xn vector? Thanks!

Accepted Answer

John D'Errico
John D'Errico on 1 Oct 2019
Edited: John D'Errico on 1 Oct 2019
You need to start learning MATLAB. That is, actually learn to use vectors, matrices, not just work with single numbers, and loops. Until you do, you will continue to have these problems.
Here is one way to do what you asked for. There are surely a zillion others.
v = 1:10;
vny = v.*(mod(1:numel(v),2)*2 - 1)
vny =
1 -2 3 -4 5 -6 7 -8 9 -10
The point is to start thinking in terms of a vector and vector operations, tools that operate on every element of a vector in one call.

More Answers (2)

Daniel M
Daniel M on 3 Oct 2019
Here is another way:
function vny = byt_tecken(v)
vny = v.*-(-1).^(1:numel(v));
end

James Tursa
James Tursa on 3 Oct 2019
Or yet another of the zillion ways
vny = v;
vny(2:2:end) = -vny(2:2:end);

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R2019b

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