Hi everyone,

I'm just a newbee to VBA/Excel. For a project, I have to write a function to calculate the eigenvectors and eigenvalues of a matrix using the "Power Method". I've tried searching the web for some help but there's not much out there. Essentially, I want to input a matrix from the excel spreadsheet along with a tolerance level (i.e. two inputs).

The function then calculates the covariance matrix, call this M (m x m), of the input data. You then make an initial guess of the eigenvector, let's say this is a vector of 1's (m x 1) (call this x), you multiply the two together to get

y=Mx

You then calculate beta which is the element of y with the largest modulus. And, recalculate x as

x=(1/beta)y

and then calculate new y, y=Mx

This is done iteratively until the difference between the old x and new x is less than the tolerance level.

The normalised x, i.e. (1/sqrt(sum(x^2)))*x , call this v, is the first prinicipal component and the last value of beta is the associated eigenvalue.

A new M is calculated as Mnew = M-beta*v*transpose(v)

And, the whole procedure is repeat for Mnew to get the second prinicipal component and associated eigenvalue. The is done m times.

I want to output all the eigenvectors (prinicipal components) and eigenvalues to some location in the spreadsheet.


I would be extremely grateful if someone could assist me with writing this function or providing some pointers.


Regards,
John