## Fibonacci numbers
## Plot Fibonacci spiral

library(shape) ## we need it for plotting

## Use install.packages("shape") if your R version does not know the
## shape package

## Function to produce the spiral plot
plot.Fib <- function(x) {
    plot(-max(x):max(x), -max(x):max(x), type="n",
         xlab="", ylab="", main="Fibonacchi spiral") # empty plot
    x.coor <- c(0,0, cumsum(x*rep(c(1,0,-1,0), length=length(x)))) # x-coordinate for center of circle
    y.coor <- c(0,0, cumsum(x*rep(c(0,1,0,-1), length=length(x)))) # y-coordinate for center "    "
    a1 <- 0:length(x)*pi/2 #angle start
    a2 <- 1:(length(x)+1)*p/2 #angle end
    for (i in 1:length(x)) {
        plotcircle(r = x[i], mid = c(x.coor[i],y.coor[i]),
                   from = a1[i], to = a2[i]) # plot the quartercircles
    }
}

# Not-so-efficient function to generate Fibonacci numbers
Fibonacci <- function(n) {
    if (!is.finite(n) || n < 1) stop("'n' must be number >= 1")
    if (n==1) {
        x <- 0
    } else {
        x <- c(0,1)
        while (length(x) < n) {
            k <- length(x)
            x[k+1] <- x[k] + x[k-1]
        }
    } # end else

    plot.Fib(x) # finally call the plot function defined above
    x           # and return the full series
}