pca <- function(X) {

  if (missing(X)) {
    cat("Usage: r <- pca(X)
      X is nSamples x nComponents
      r$V is nComponents x nComponents eigenvector matrix  (X %*% V)
      r$values are the nComponents eigenvalues \n")
    return(invisible(NULL))
  }

  eigenResult <- eigen(cov(X))
  list(V = eigenResult$vectors, values=eigenResult$values)
}