# Haskell Mandelbrot

I wrote a program (years ago) in Haskell that generated the image above of the Mandelbrot set. I really like Haskell, but I haven't spent enough time with it and never really wrapped my head around monads. I'd like to dive back into it when I get the time.

Anyway, the program I used to generate the fractal is below. I'm *not* a Haskell guru, so if the code is an abomination and you know how to improve it, please share in the comments! It would be cool to improve my Haskell skills. I wrote this years ago:

module Main where import Data.Complex import Data.Char import qualified Data.ByteString.Char8 as C -- For file output -- Constants maxIter :: Int -- Max iterations maxIter = 750 width :: Int -- Image width height :: Int -- Image height width = 400 height = 400 -- Note: aspect ratio of (minX, minY), (maxX, maxY) must -- match aspect ratio of (width, height) minX :: Double -- Min x-coordinate of graph maxX :: Double -- Max x-coordinate of graph minY :: Double -- Min y-coordinate of graph maxY :: Double -- Max y-coordinate of graph -- For the zoomed in part of the Mandelbrot: --minX = -0.826341244461360116 --maxX = -0.8026423086165848822 --minY = -0.2167936114403439588 --maxY = -0.193094675595568725 --For a full view of the mandelbrot minX = -2.5 maxX = 1.5 minY = -2 maxY = 2 -- The actual fractal part -- It basically works on a matrix, which we will call M, that represents a grid of -- points on the graph. Essentially, M[i, j] is (xList[j], yList[i]) xList :: [Double] yList :: [Double] xList = [minX, (minX + ((maxX - minX) / (fromIntegral width - 1)))..maxX] yList = reverse [minY,(minY + ((maxY - minY) / (fromIntegral height - 1)))..maxY] row :: Double -> C.ByteString -- A row of image bytes for a given y-coordinate row y = C.pack [frac (x :+ y) (0 :+ 0) 0 | x <- xList] -- For Mandelbrot set --row y = C.pack [frac ((-0.1) :+ (0.8)) (x :+ y) 0 | x <- xList] -- For Julia set etaFraction :: Complex Double -> Double etaFraction z = (log (log (magnitude z))) / log 2 smoothEta :: Int -> Complex Double -> Double -- Smooth escape time algorithm value smoothEta iter z = (fromIntegral iter - etaFraction z) / fromIntegral maxIter color :: Int -> Complex Double -> Double -- Gets the color for the point, in range [0, 1] color iter z = 1 - smoothEta iter z -- Smooth escape time algorithm (and invert) --color iter z = fromIntegral iter / fromIntegral maxIter interpolate :: Double -> Char -- Adds an interpolation curve for interpolating color interpolate v = chr (truncate ((v ^ 12) * 255)) -- Polynomial curve --interpolate v = chr (truncate(v * 255)) -- Linear frac :: Complex Double -> Complex Double -> Int -> Char -- The actual fractal algorithm! frac c z iter | iter >= maxIter = chr 255 -- never escaped, return color value of 255 | otherwise = let z' = z * z + c in if ((realPart z') * (realPart z') + (imagPart z') * (imagPart z')) > 4 then interpolate (color iter z') else frac c z' (iter + 1) -- The file output pgmHeader :: C.ByteString pgmHeader = C.pack ("P5\n" ++ (show width) ++ " " ++ (show height) ++ "\n255\n") main = C.writeFile "fractal.pgm" (C.append pgmHeader (C.concat [(row y) | y <- yList]))

And some pictures from this program (each image has had some constants tweaked):

A Julia set based on (0.285, -0.01i). I actually edited the brightness/contrast in post-processing on this one to really bring out the spirals.