Add logistic-map.md

rust/logistic-map.md

+This snippet of code demonstrates how to create an infinitely long `Iterator`
+for a iterated function. A data structure stores some state, in this case `x`,
+that is then fed into the actual function at each step. 
+
+```rust
+fn logistic_map(x: f64, r: f64) -> f64 {
+    x * r * (1.0 - x)
+}
+   
+struct LogisticMap {
+    r: f64,
+    x: f64,
+}
+
+impl Iterator for LogisticMap {
+    type Item = f64;
+    
+    fn next(&mut self) -> Option<Self::Item> {
+        let new_x = logistic_map(self.x, self.r);
+        self.x = new_x;
+        Some(new_x)
+    } 
+}
+
+fn main() {
+    let res: Vec<f64> = LogisticMap{r: 3.995, x: 0.5}.take(20).collect();
+    println!("{:#?}", res);
+}
+```
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