add binom coeff func

Author: tbrown122387

include/rv_eval.h

@@ -68,6 +68,13 @@ double inv_logit(const double &r);
 double log_inv_logit(const double &r);
 
 
+////////////////////////////////////////////////
+///////      Other Math Functions        ///////
+////////////////////////////////////////////////
+
+
+unsigned int nChooseK(unsigned int n, unsigned int k);
+
 
 ////////////////////////////////////////////////
 /////////       double evals           /////////

src/rv_eval.cpp

@@ -52,6 +52,21 @@ double rveval::log_inv_logit(const double& r)
 }
 
 
+unsigned int sf::nChoosek( unsigned int n, unsigned int k )
+{
+    if (k > n) return 0;
+        if (k * 2 > n) /*return*/ k = n-k;  //remove the commented section
+        if (k == 0) return 1;
+
+    int result = n;
+    for( int i = 2; i <= k; ++i ) {
+        result *= (n-i+1);
+        result /= i;
+    }
+    return result;
+}
+
+
 double rveval::evalUnivNorm(const double &x, const double &mu, const double &sigma, bool log)
 {
     double exponent = -.5*(x - mu)*(x-mu)/(sigma*sigma);