Added Iterated function system in Rust

contents/IFS/IFS.md

@@ -146,6 +146,8 @@ Here, instead of tracking children of children, we track a single individual tha
 [import:4-16, lang:"coconut"](code/coconut/IFS.coco)
 {% sample lang="java" %}
 [import:16-39, lang:"java"](code/java/IFS.java)
+{% sample lang="rs" %}
+[import:11-29, lang:"rust"](code/rust/IFS.rs)
 {% endmethod %}
 
 If we set the initial point to the on the equilateral triangle we saw before, we can see the Sierpinski triangle again after a few thousand iterations, as shown below:
@@ -232,6 +234,8 @@ In addition, we have written the chaos game code to take in a set of points so t
 [import, lang:"coconut"](code/coconut/IFS.coco)
 {%sample lang="java" %}
 [import, lang:"java"](code/java/IFS.java)
+{% sample lang="rs" %}
+[import, lang:"rust"](code/rust/IFS.rs)
 {% endmethod %}
 
 ### Bibliography

contents/IFS/code/rust/IFS.rs

@@ -0,0 +1,49 @@
+use std::fs::File;
+use std::io::Write;
+
+// require create rand:
+use rand::prelude::SliceRandom;
+use rand::Rng;
+
+type Point = (f64, f64);
+
+// This function simulates a "chaos game"
+fn chaos_game(n: u32, shape_points: Vec<Point>) -> Vec<Point> {
+    let mut rng = rand::thread_rng();
+
+    // initialize the output vector and the initial point
+    let mut output_points: Vec<Point> = Vec::new();
+    let mut point = (rng.gen(), rng.gen());
+
+    for _ in 0..n {
+        output_points.push(point);
+
+        let tmp = shape_points
+            .choose(&mut rng)
+            .expect("could not choose a shape point");
+
+        point = (0.5 * (point.0 + tmp.0), 0.5 * (point.1 + tmp.1));
+    }
+
+    output_points
+}
+
+fn main() {
+
+    // This will generate a Sierpinski triangle with a chaos game of n points for an
+    // initial triangle with three points on the vertices of an equilateral triangle:
+    //     A = (0.0, 0.0)
+    //     B = (0.5, sqrt(0.75))
+    //     C = (1.0, 0.0)
+    // It will output the file sierpinski.dat, which can be plotted after
+
+    let shape_points = vec![(0.0, 0.0), (0.5, 0.75_f64.sqrt()), (1.0, 0.0)];
+
+    let output_points = chaos_game(10000, shape_points);
+
+    let mut file = File::create("sierpinski.dat").expect("Unable to open/create the file");
+
+    for (x, y) in output_points {
+        writeln!(&mut file, "{}\t{}", x, y).expect("Unable to write to file");
+    }
+}

contents/approximate_counting/approximate_counting.md

@@ -366,6 +366,8 @@ As we do not have any objects to count, we will instead simulate the counting wi
 [import, lang:"cpp"](code/c++/approximate_counting.cpp)
 {% sample lang="python" %}
 [import, lang:"python"](code/python/approximate_counting.py)
+{% sample lang="java" %}
+[import, lang:"java"](code/java/ApproximateCounting.java)
 {% endmethod %}
 
 ### Bibliography

contents/approximate_counting/code/java/ApproximateCounting.java

@@ -0,0 +1,82 @@
+import java.lang.Math;
+import java.util.stream.DoubleStream;
+
+public class ApproximateCounting {
+
+    /*
+     * This function taks
+     *   - v: value in register
+     *   - a: a scaling value for the logarithm based on Morris's paper
+     * It returns the approximate count
+     */
+    static double n(double v, double a) {
+	return a * (Math.pow(1 + 1 / a, v) - 1);
+    }
+
+
+    /*
+     * This function takes
+     *   - v: value in register
+     *   - a: a scaling value for the logarithm based on Morris's paper
+     * It returns the new value for v
+     */
+    static double increment(double v, double a) {
+	double delta = 1 / (n(v + 1, a) - n(v, a));
+
+	if (Math.random() <= delta) {
+		return v + 1;
+	} else {
+		return v;
+	}
+    }
+
+
+
+    /*
+     * This function takes
+     *   - v: value in register
+     *   - a: a scaling value for the logarithm based on Morris's paper
+     * It returns the new value for v
+     */
+    static double approximateCount(int nItems, double a) {
+    	double v = 0;
+
+	for (int i = 1; i < nItems + 1; i++) {
+		v = increment(v, a);
+	}
+
+	return n(v, a);
+    }
+
+    /*
+     * This function takes
+     *   - nTrails: the number of counting trails
+     *   - nItems: the number of items to count
+     *   - a: a scaling value for th elogarithm based on Morris's paper
+     *   - threshold: the maximum percent error allowed
+     * It terminates the program on failure
+     */
+    static void testApproximateCount(int nTrails, int nItems, double a, double threshold) {
+	double avg = DoubleStream.generate(() -> approximateCount(nItems, a))
+			         .limit(nTrails)
+			         .average()
+				 .getAsDouble();
+
+	if (Math.abs((avg - nItems) / nItems) < threshold) {
+		System.out.println("passed");
+	}
+    }
+
+
+    public static void main(String args[]) {
+	System.out.println("testing 1,000, a = 30, 1% error");
+	testApproximateCount(100, 1_000, 30, 0.1);
+
+	System.out.println("testing 12,345, a = 10, 1% error");
+	testApproximateCount(100, 12_345, 10, 0.1);
+
+	System.out.println("testing 222,222, a = 0.5, 10% error");
+	testApproximateCount(100, 222_222, 0.5, 0.2);
+    }
+
+}