[R] Re: Mandelbrot set and C code

[Jason Turner]

Jason Turner wrote:

> ...I did a slight tweak to your mandelbrot.R code, so
> that x can be a list with components x and y.  This allows you to keep 
> zooming in using your mouse to click on the plot (one of the incredibly 
> nifty features of such sets).
> 
> Using the "tweaked" version below, call the function as you suggested:
> 
> image(mandelbrot(), col = c(heat.colors(49), "black"))
> 
> Then use locator(2) to define your next view:
> 
> image(mandelbrot(locator(2)), col = c(heat.colors(49), "black"))
> 

Of course, I would've been nice if I'd included the tweaked version.  D'ho!

#######################################################################
# Function to calculate the Mandelbrot set. This function calls a     #
# C routine in order to perform the calculations faster.              #
#                                                                     #
# Written by Mario dos Reis. September 2003                           #
# Modified: added if(is.list(x)){...} at start to check if co-ords    #
#           are from locator() or similar - jason turner oct 2 2003   #
#######################################################################

mandelbrot <- function(x = c(-3, 1),        # x limits
                        y = c(-1.8, 1.8),    # y limits
                        nx = 600,            # x resolution
                        ny = 600,            # y resolution
                        iter = 20)           # maximun number of iterations
{
   if(is.list(x)) {
     y <- range(x$y)
     x <- range(x$x)
   }
   xcoo <- seq(x[1], x[2], len = nx) # x coordinates
   ycoo <- seq(y[1], y[2], len = ny) # y coordinates
   set = numeric(nx*ny)              # this will store the output of
                                     # the C routine

   # This is the call to the C function itself
   the.set = .C("mandelbrot",
     xcoo = as.double(xcoo),
     ycoo = as.double(ycoo),
     nx = as.integer(nx),
     ny = as.integer(ny),
     set = as.integer(set),
     iter = as.integer(iter))$set

   # Create a list with elements x, y and z,
   # suitable for image(), persp(), etc. and return it.
   return(list(x = xcoo, y = ycoo, z = matrix(the.set, ncol = ny, byrow 
= T)));
}


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