More sophisticated code than a for loop with i is large

Hi there I am trying to calculate a scatter matrix for some data. so basically my Eigen values are in a matrix of the form; [e11 e12 e13; e21 e22 e23; e31 e32 e33; ...... e101 e102e103]

and my scatter matrix is of the form;

[e11^2 + e21^2 + e31^2 + ... e101^2, e11e12 + e21e22 + ... +e101e102, e11e13 + ... e101e103; e11e12 + e21e22 + ... +e101e102, e12+e22+e32+..e102, e12e13+e22e23+...+e102e103; e11e13 + ... e101e103, e12e13+e22e23+...+e102e103; e13^2+e23^2+...+e103^2]

Now in some cases instead of n = 10 as is the case above n =in the thousadns. is there a neat way to code for this?

[Jan]

How is "n=10" related to the posted code. I think, names like e101e103 are such ugly, that it is near to impossible to read the code.

Answer 1

[Andrei Bobrov]

Let e = [e11 e12 e13; e21 e22 e23; e31 e32 e33; ...... e101 e102e103];

out = e.'*e;
out(2,2) = sum(e(:,2));

Answer 2

[Hugo]

Please notice that in the "scatter matrix" that you showed as an example there are elements that are repeated, and the structure is not exactly a matrix.

So, it seems that the matrix of eigenvalues, let's say A, is of size n x 3. Is the scatter matrix of this data what you want? You can simply do

A'*A, and it will return a 3x3 matrix where each element Aij has the values:

Aij= sum_n ( eni * enj ), which partially coincides with your example.