# [R] converting an R function into VBA

From: Eric yang <yang_eric9_at_yahoo.com>
Date: Sat, 21 Jun 2008 07:06:31 -0700 (PDT)

Hi everyone,

I want to convert an R function into VBA for calculating the eigenvectors and eigenvalues of a matrix using the "Power Method". The function is:

PowerMethod <- function(x, tolerance) {
ааа my.mat <- var(x[,-1], na.method="available")
ааа matSize <- dim(my.mat)
ааа eigenVec <- matrix(NA, nrow=matSize, ncol=matSize)
ааа eigenVal <- rep(NA, matSize)
ааа for(j in 1:matSize) {

```ааааааа x <- rep(1, matSize)
ааааааа yk <- x + tolerance + 1
аааааааа while(all(x-yk<tolerance)) {
ааааааааааа yk <- my.mat%*%x
ааааааааааа beta <- yk[abs(yk)==max(abs(yk))]
ааааааааааа x <- (1/beta)*yk
ааааааа }
ааааааа eigenVec[,j] <- (1/sqrt(sum(x^2)))*x
ааааааа eigenVal[j] <- beta
ааааааа my.mat <- my.mat - eigenVal[j]*eigenVec[,j]%*%t(eigenVec[,j])
```

ааа }
ааа list(eigenVec, eigenVal)

}

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 repeated 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 in converting this function to VBA.

Eric

```
[[alternative HTML version deleted]]

______________________________________________
```
R-help_at_r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Sat 21 Jun 2008 - 14:09:06 GMT

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.2.0, at Sat 21 Jun 2008 - 17:30:52 GMT.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help. Please read the posting guide before posting to the list.