How to solve this index exceeds matrix dimensions error?

Hello this is my code:

N = 30;
  Sw = 0;
  ni=8; %numero campioni
  for i = 1:N
      for j = 1:ni
          x_diff = X(i,j) - mean(X(i,2));
          Sw = Sw + (x_diff * x_diff');
      end
  end

    Sb = 0;

    for i = 1:N
        x_diff = mean(X(i,N)) - mean(X);
        Sb = Sb + (N(i) * x_diff * x_diff');
    end
how can i solve the problem of the index exceeds matrix dimensions?

[Birdman]

What is X?

[Jessica Frau]

X is a vector X = (N, 1)

[Birdman]

If X has one column as you say, then why you try to reach to 8th column in first nested for loop and 2nd column in mean operation?

   for i = 1:N
        for j = 1:ni
            x_diff = X(i,j) - mean(X(i,2));
            Sw = Sw + (x_diff * x_diff');
        end
    end

[Jessica Frau]

Well, I understand the error, but now I don't know how to create the scattering matrix with my data set X. If you can help me this are the formulas of the scattering matrix.

[Guillaume]

I don't understand your equations, particularly why there is a transpose symbol on something that look like scalar values, but in any case, it is clear that X is supposed to be at least a 2D matrix.

If you don't have a 2D matrix I'm not sure how we can help.

Answer 1

[Guillaume]

As you've stated X is a Nx1 vector. Yet, you have:

X(i, j)
X(i, 2)
X(i, N)

in your code. How are you expecting that to work?