From b31d5b814e17e45e04c6941b5ed698b85e8807af Mon Sep 17 00:00:00 2001 From: "Steinar H. Gunderson" Date: Thu, 11 Oct 2007 00:04:28 +0200 Subject: [PATCH] Precompute the binomial as a single value instead of two separate ones. --- foosrank.cpp | 25 ++++++++++++------------- 1 file changed, 12 insertions(+), 13 deletions(-) diff --git a/foosrank.cpp b/foosrank.cpp index ba24d02..fc968cd 100644 --- a/foosrank.cpp +++ b/foosrank.cpp @@ -15,7 +15,7 @@ static const double rating_constant = 455.0; using namespace std; double prob_score(int k, double a, double rd); -double prob_score_real(int k, double a, double prodai, double kfac, double rd_norm); +double prob_score_real(int k, double a, double binomial, double rd_norm); double prodai(int k, double a); double fac(int x); @@ -56,16 +56,16 @@ double simpson_integrate(const T &evaluator, double from, double to, double step // double prob_score(int k, double a, double rd) { - return prob_score_real(k, a, prodai(k, a), fac(k-1), rd/rating_constant); + return prob_score_real(k, a, prodai(k, a) / fac(k-1), rd/rating_constant); } -// Same, but takes in Product(a+i, i=1..k-1) and (k-1)! as an argument in +// Same, but takes in binomial(a+k-1, k-1) as an argument in // addition to a. Faster if you already have that precomputed, and assumes rd // is already divided by 455. -double prob_score_real(int k, double a, double prodai, double kfac, double rd_norm) +double prob_score_real(int k, double a, double binomial, double rd_norm) { - double nom = prodai * pow(2.0, rd_norm * a); - double denom = kfac * pow(1.0 + pow(2.0, rd_norm), k+a); + double nom = binomial * pow(2.0, rd_norm * a); + double denom = pow(1.0 + pow(2.0, rd_norm), k+a); return nom/denom; } @@ -109,14 +109,14 @@ class ProbScoreEvaluator { private: int k; double a; - double prodai_precompute, kfac_precompute, r1, mu2, sigma2, winfac; + double binomial_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) {} + ProbScoreEvaluator(int k, double a, double binomial_precompute, double r1, double mu2, double sigma2, double winfac) + : k(k), a(a), binomial_precompute(binomial_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 probscore = prob_score_real(k, a, binomial_precompute, (x - r1)*winfac); double z = (x - mu2)/sigma2; double gaussian = exp(-(z*z/2.0)); return probscore * gaussian; @@ -125,11 +125,10 @@ public: double opponent_rating_pdf(int k, double a, double r1, double mu2, double sigma2, double winfac) { - double prodai_precompute = prodai(k, a); - double kfac_precompute = fac(k-1); + double binomial_precompute = prodai(k, a) / fac(k-1); winfac /= rating_constant; - return simpson_integrate(ProbScoreEvaluator(k, a, prodai_precompute, kfac_precompute, r1, mu2, sigma2, winfac), 0.0, 3000.0, int_step_size); + return simpson_integrate(ProbScoreEvaluator(k, a, binomial_precompute, r1, mu2, sigma2, winfac), 0.0, 3000.0, int_step_size); } // normalize the curve so we know that A ~= 1 -- 2.39.2