Precompute the binomial as a single value instead of two separate ones.

diff --git a/foosrank.cpp b/foosrank.cpp
index ba24d0254e69fc32a58f7deca9c08856dc5d6b39..fc968cd647b86baa5591205f6bd2b47d9507544c 100644 (file)
--- 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