added von mises distributionb

quick&dirty: added activity to the grid-walkers

math/distribution/Bessel.h

@@ -0,0 +1,57 @@
+#ifndef BESSEL_H
+#define BESSEL_H
+
+namespace Distribution {
+
+	/** helper class */
+	template <typename T> class Bessel {
+
+	public:
+
+		/**
+		 * calculation for I_v(z)
+		 * https://en.wikipedia.org/wiki/Bessel_function
+		 * http://www.boost.org/doc/libs/1_35_0/libs/math/doc/sf_and_dist/html/math_toolkit/special/bessel/mbessel.html
+		 */
+		T getModified(const int v, const T z) const {
+
+			// running factorials (updated within for-loops)
+			uint64_t runFac1 = 1;
+			uint64_t runFac2 = factorial(v);	// Delta(k+v+1) = (k+v+1-1)! = (k+v)! [k starts at 0] -> (v)!
+
+			// running potential
+			T runPot = 1;
+			const T pot = T(0.25) * z * z;
+
+			// start for-loop at k=1 instead of k=0. allows for running factorial without using if (k==0)
+			T sum = 0;
+			for (int k = 0; k < 16; ) {
+				sum += runPot / runFac1 / runFac2;
+				++k;
+				runFac1 *= k;
+				runFac2 *= k;
+				runPot *= pot;
+			}
+
+			// done
+			return std::pow( (T(0.5) * z), v) * sum;
+
+		}
+
+	private:
+
+
+
+
+
+		static uint64_t factorial(const int n) {
+			uint64_t res = 1;
+			for (int i = 2; i <= n; ++i) {res *= i;}
+			return res;
+		}
+
+	};
+
+}
+
+#endif // BESSEL_H