From: Steinar H. Gunderson <sesse@debian.org>
Date: Wed, 10 Oct 2007 22:01:24 +0000 (+0200)
Subject: Make a common function for the Simpson integration stuff.
X-Git-Url: https://git.sesse.net/?p=foosball;a=commitdiff_plain;h=cfdaa9835398e670f3847222f293545952155918

Make a common function for the Simpson integration stuff.
---

diff --git a/foosrank.cpp b/foosrank.cpp
index f166182..ba24d02 100644
--- a/foosrank.cpp
+++ b/foosrank.cpp
@@ -19,6 +19,25 @@ double prob_score_real(int k, double a, double prodai, double kfac, double rd_no
 double prodai(int k, double a);
 double fac(int x);
 
+// Numerical integration using Simpson's rule
+template<class T>
+double simpson_integrate(const T &evaluator, double from, double to, double step)
+{
+	int n = int((to - from) / step + 0.5);
+	double h = (to - from) / n;
+	double sum = evaluator(from);
+
+	for (int i = 1; i < n; i += 2) {
+		sum += 4.0 * evaluator(from + i * h);
+	}
+	for (int i = 2; i < n; i += 2) {
+		sum += 2.0 * evaluator(from + i * h);
+	}
+	sum += evaluator(to);
+
+	return (h/3.0) * sum;
+}
+
 // probability of match ending k-a (k>a) when winnerR - loserR = RD
 //
 //   +inf  
@@ -86,7 +105,23 @@ double fac(int x)
 // Set the last parameter to 1.0 if player 1 won, or -1.0 if player 2 won.
 // In the latter case, ProbScore will be given (r1-r2) instead of (r2-r1).
 //
-static inline double evaluate_int_point(int k, double a, double prodai_precompute, double kfac_precompute, double r1, double mu2, double sigma2, double winfac, double x);
+class ProbScoreEvaluator {
+private:
+	int k;
+	double a;
+	double prodai_precompute, kfac_precompute, r1, mu2, sigma2, winfac;
+
+public:
+	ProbScoreEvaluator(int k, double a, double prodai_precompute, double kfac_precompute, double r1, double mu2, double sigma2, double winfac)
+		: k(k), a(a), prodai_precompute(prodai_precompute), kfac_precompute(kfac_precompute), r1(r1), mu2(mu2), sigma2(sigma2), winfac(winfac) {}
+	inline double operator() (double x) const
+	{
+		double probscore = prob_score_real(k, a, prodai_precompute, kfac_precompute, (x - r1)*winfac);
+		double z = (x - mu2)/sigma2;
+		double gaussian = exp(-(z*z/2.0));
+		return probscore * gaussian;
+	}
+};
 
 double opponent_rating_pdf(int k, double a, double r1, double mu2, double sigma2, double winfac)
 {
@@ -94,27 +129,7 @@ double opponent_rating_pdf(int k, double a, double r1, double mu2, double sigma2
 	double kfac_precompute = fac(k-1);
 	winfac /= rating_constant;
 
-	int n = int(3000.0 / int_step_size + 0.5);
-	double h = 3000.0 / double(n);
-	double sum = evaluate_int_point(k, a, prodai_precompute, kfac_precompute, r1, mu2, sigma2, winfac, 0.0);
-
-	for (int i = 1; i < n; i += 2) {
-		sum += 4.0 * evaluate_int_point(k, a, prodai_precompute, kfac_precompute, r1, mu2, sigma2, winfac, i * h);
-	}
-	for (int i = 2; i < n; i += 2) {
-		sum += 2.0 * evaluate_int_point(k, a, prodai_precompute, kfac_precompute, r1, mu2, sigma2, winfac, i * h);
-	}
-	sum += evaluate_int_point(k, a, prodai_precompute, kfac_precompute, r1, mu2, sigma2, winfac, 3000.0);
-
-	return (h/3.0) * sum;
-}
-
-static inline double evaluate_int_point(int k, double a, double prodai_precompute, double kfac_precompute, double r1, double mu2, double sigma2, double winfac, double x)
-{
-	double probscore = prob_score_real(k, a, prodai_precompute, kfac_precompute, (x - r1)*winfac);
-	double z = (x - mu2)/sigma2;
-	double gaussian = exp(-(z*z/2.0));
-	return  probscore * gaussian;
+	return simpson_integrate(ProbScoreEvaluator(k, a, prodai_precompute, kfac_precompute, r1, mu2, sigma2, winfac), 0.0, 3000.0, int_step_size);
 }
 
 // normalize the curve so we know that A ~= 1