Creating [-1 1] matrix given length n

Hi,

I want to create N length long [-1 1] matrix,

For example: Length=2

Output:

[ 1  1
  1 -1
 -1  1
 -1 -1]

Length = 3

Output:

[ 1  1  1
  1  1 -1
  1 -1  1
 -1  1  1
   ......
 -1 -1 -1]

And so on, How can do that?

Answer 1

[Sriram Tadavarty]

Hi Alice,

You can try the following:

len = 2;
N = 2^len;
bi = de2bi(N-1:-1:0);  % Convert decimal numbers in to binary
bi(bi==0) = -1; % Replace the values of 0 with -1

Hope this helps.

Regards,

Sriram

[Sriram Tadavarty]

Hi Alice,

If the answer is helpful for the question asked, do accept the answer. I suggest you to start a new question for this. Anyhow i can provide some insights of how this can be done here.

To perform the circular shift, you can use circshift function. To iterate the same for multiple times, use a for loop.

For example, for row selected

row = [1 -1 1];
crow = circshift(row,1); % This will provide the value of [1 1 -1]
% Now perform the element wise matrix multiplication and add them
out = sum(row.*crow); % This will give you the -1
% Based on out, display the string accordingly

Hope this helps.

Regards,

Sriram

Answer 2

[Ameer Hamza]

See combvec():

Length = 3;
x = mat2cell(repmat([1 -1], Length, 1), ones(Length,1), 2);
out = combvec(x{:})';