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Clojure Programming by Brian Carper, Christophe Grand, Chas Emerick

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Visualizing the Mandelbrot Set in Clojure

Let’s take a look at a somewhat more interesting example than the overused Fibonacci and prime number generators that are often used for microbenchmarking numeric performance. Visualizing the Mandelbrot Set[349] (or really, any fractal shape visualization) has long been a common practicum, and it will serve well here as a demonstration of how to optimize numeric algorithms in Clojure.

The Mandelbrot Set is defined by a complex polynomial that is applied iteratively:

zk+1 = zk2 + c

where c (a complex number) is a member of the Mandelbrot Set if zk+1 is bounded as k increases when z0 is initialized to 0. c’s that produce unbounded results from this calculation are said to escape to infinity.

First, let’s look at a naive implementation of the Mandelbrot Set in Clojure,[350] which includes a couple utility functions for rendering the results of that implementation:

Example 11-4. Mandelbrot Set in Clojure

(ns clojureprogramming.mandelbrot (:import java.awt.image.BufferedImage (java.awt Color RenderingHints))) (defn- escape "Returns an integer indicating how many iterations were required before the value of z (using the components `a` and `b`) could be determined to have escaped the Mandelbrot set. If z will not escape, -1 is returned." [a0 b0 depth] (loop [a a0 b b0 iteration 0] (cond (< 4 (+ (* a a) (* b b))) iteration (>= iteration depth) -1 :else (recur (+ a0 (- (* a a) (* b b))) (+ b0 (* 2 (* a b))) (inc iteration))))) (defn mandelbrot "Calculates ...

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