[R] why I could not reproduce the Mandelbrot plot demonstrated on R wiki

[Peter Dalgaard]

On 09/24/2010 10:41 PM, xin wei wrote:
> 
> I am trying to reproduce the nice looking of Mandelbrot demonstrated by R
> wiki page by the following code:
> 
> library(caTools)        # external package providing write.gif function
> jet.colors = colorRampPalette(c("#00007F", "blue", "#007FFF", "cyan",
> "#7FFF7F", 
>                                 "yellow", "#FF7F00", "red", "#7F0000")) 
> m = 600                 # define size
> C = complex( real=rep(seq(-1.8,0.6, length.out=m), each=m ), 
>              imag=rep(seq(-1.2,1.2, length.out=m), m ) ) 
> C = matrix(C,m,m)       # reshape as square matrix of complex numbers
> Z = 0                   # initialize Z to zero
> X = array(0, c(m,m,20)) # initialize output 3D array
> for (k in 1:20) {       # loop with 20 iterations
>   Z = Z^2+C             # the central difference equation  
>   X[,,k] = exp(-abs(Z)) # capture results
> } 
> write.gif(X, "Mandelbrot.gif", col=jet.colors, delay=100)

Hmm, I couldn't be bothered with the caTools, but it looks fine for me with

image(X[,,20],col=jet.colors(100))

Perhaps you need jet.colors(n) as well?



> however, the gif file created by this looks much worse than what is shown on
> R wiki page, see the comparison as follows (left one is what i created)
> 
> http://r.789695.n4.nabble.com/file/n2591429/Picture1.png 

Save for the odd color scheme, the one on the left looks like a
Mandelbrot set, the one on the right appears to be iteration 4. I
couldn't find your original source for this on wiki.r-project.org?


-- 
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com