Initial data commit

Task/Statistics-Normal-distribution/D/statistics-normal-distribution.d

@@ -0,0 +1,27 @@
+import std.stdio, std.random, std.math, std.range, std.algorithm,
+       statistics_basic;
+
+struct Normals {
+    double mu, sigma;
+    double[2] state;
+    size_t index = state.length;
+    enum empty = false;
+
+    void popFront() pure nothrow { index++; }
+
+    @property double front() {
+        if (index >= state.length) {
+            immutable r = sqrt(-2 * uniform!"]["(0., 1.0).log) * sigma;
+            immutable x = 2 * PI * uniform01;
+            state = [mu + r * x.sin, mu + r * x.cos];
+            index = 0;
+        }
+        return state[index];
+    }
+}
+
+void main() {
+    const data = Normals(0.0, 0.5).take(100_000).array;
+    writefln("Mean: %8.6f, SD: %8.6f\n", data.meanStdDev[]);
+    data.map!q{ max(0.0, min(0.9999, a / 3 + 0.5)) }.showHistogram01;
+}