June 2018 Update

Task/Percolation-Mean-run-density/Kotlin/percolation-mean-run-density.kotlin

@@ -0,0 +1,40 @@
+// version 1.2.10
+
+import java.util.Random
+
+val rand = Random()
+const val RAND_MAX = 32767
+
+// just generate 0s and 1s without storing them
+fun runTest(p: Double, len: Int, runs: Int): Double {
+    var cnt = 0
+    val thresh = (p * RAND_MAX).toInt()
+    for (r in 0 until runs) {
+        var x = 0
+        var i = len
+        while (i-- > 0) {
+            val y = if (rand.nextInt(RAND_MAX + 1) < thresh) 1 else 0
+            if (x < y) cnt++
+            x = y
+        }
+    }
+    return cnt.toDouble() / runs / len
+}
+
+fun main(args: Array<String>) {
+    println("running 1000 tests each:")
+    println(" p\t   n\tK\tp(1-p)\t     diff")
+    println("------------------------------------------------")
+    val fmt = "%.1f\t%6d\t%.4f\t%.4f\t%+.4f (%+.2f%%)"
+    for (ip in 1..9 step 2) {
+        val p = ip / 10.0
+        val p1p = p * (1.0 - p)
+        var n = 100
+        while (n <= 100_000) {
+            val k = runTest(p, n, 1000)
+            println(fmt.format(p, n, k, p1p, k - p1p, (k - p1p) / p1p * 100))
+            n *= 10
+        }
+        println()
+    }
+}