Generate a matrix with alternative positive and negative values with ones
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Jorge Luis Paredes Estacio
on 21 Jul 2023
Commented: Jorge Luis Paredes Estacio
on 21 Jul 2023
Hello, Any idea how to generate a matrix with ones with positive and negative values. For example
We know,
A=ones(n,1)=[1;1;1;1], if n=4
I would like a matrix like this:
A=[1;-1;1;-1]
However, n will change of size depending on the processed data.
On the other hand, I would like to generate a matrix with the following form
if n=10
A=[1;0.5;0;-0.5;-1;-.5;0;0.5;1;0.5], the n value can change depending on the uploaded data.
Thank you.
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Accepted Answer
John D'Errico
on 21 Jul 2023
Edited: John D'Errico
on 21 Jul 2023
Learn to use various tools in MATLAB. In this case, mod will help you. Forexample:
n = 4;
mod(1:n,2)
Does that get you close to what you want? You want a column. But that is easy. And you want +/-1. Also easy.
mod((1:n)',2)*2 - 1
Simple enough. Again, look for your target, and think of what you can do to get there.
As for the second case, it is not clear what general pattern you expect in there. If n was larger, would the step still be 0.5? Would this be a periodic function? Or a simple V-shape?
2 Comments
John D'Errico
on 21 Jul 2023
Edited: John D'Errico
on 21 Jul 2023
A v-shape is most simply achieved using abs. Again, look for something that gets you close to your target. For example:
n = 9;
abs((1:n) - (n+1)/2)
Now we can scale those numbers. and put in a shift.
abs((1:n) - (n+1)/2)/2
V = abs((1:n) - (n+1)/2)/2 - 1
plot(V,'-o')
More Answers (2)
Dyuman Joshi
on 21 Jul 2023
n = 10;
vec = (0:n-1)';
%Array A
A = cospi(vec)
%Array B
vec0 = vec+4;
B = 4*abs(vec0/8-floor(vec0/8+0.5))-1
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