1 files changed, 17 insertions, 4 deletions

diff --git a/gi/clda/src/ccrp.h b/gi/clda/src/ccrp.h
index 47f364f2..9b1c5284 100644
--- a/gi/clda/src/ccrp.h
+++ b/gi/clda/src/ccrp.h
@@ -18,12 +18,19 @@ class CCRP {
  public:
   CCRP(double disc, double conc) : num_tables_(), num_customers_(), discount_(disc), concentration_(conc) {}
 
+  void clear() {
+    num_tables_ = 0;
+    num_customers_ = 0;
+    dish_locs_.clear();
+  }
+
   unsigned num_tables(const Dish& dish) const {
     const typename std::tr1::unordered_map<Dish, DishLocations, DishHash>::const_iterator it = dish_locs_.find(dish);
     if (it == dish_locs_.end()) return 0;
     return it->second.table_counts_.size();
   }
 
+  // returns +1 or 0 indicating whether a new table was opened
   int increment(const Dish& dish, const double& p0, MT19937* rng) {
     DishLocations& loc = dish_locs_[dish];
     bool share_table = false;
@@ -56,6 +63,7 @@ class CCRP {
     return (share_table ? 0 : 1);
   }
 
+  // returns -1 or 0, indicating whether a table was closed
   int decrement(const Dish& dish, MT19937* rng) {
     DishLocations& loc = dish_locs_[dish];
     assert(loc.total_dish_count_);
@@ -66,11 +74,13 @@ class CCRP {
       return -1;
     } else {
       int delta = 0;
-      double r = rng->next() * (loc.total_dish_count_ - loc.table_counts_.size() * discount_);
+      // sample customer to remove UNIFORMLY. that is, do NOT use the discount
+      // here. if you do, it will introduce (unwanted) bias!
+      double r = rng->next() * loc.total_dish_count_;
       --loc.total_dish_count_;
       for (typename std::list<unsigned>::iterator ti = loc.table_counts_.begin();
            ti != loc.table_counts_.end(); ++ti) {
-        r -= (*ti - discount_);
+        r -= *ti;
         if (r <= 0.0) {
           if ((--(*ti)) == 0) {
             --num_tables_;
@@ -107,7 +117,9 @@ class CCRP {
     double lp = 0.0;
     if (num_customers_) {
       const double r = lgamma(1.0 - discount_);
-      lp = lgamma(concentration_) - lgamma(concentration_ + num_customers_) + num_tables_ * discount_ + lgamma(concentration_ / discount_ + num_tables_) - lgamma(concentration_ / discount_);
+      lp = lgamma(concentration_) - lgamma(concentration_ + num_customers_)
+           + num_tables_ * discount_ + lgamma(concentration_ / discount_ + num_tables_)
+           - lgamma(concentration_ / discount_);
       for (typename std::tr1::unordered_map<Dish, DishLocations, DishHash>::const_iterator it = dish_locs_.begin();
            it != dish_locs_.end(); ++it) {
         const DishLocations& cur = it->second;
@@ -119,8 +131,9 @@ class CCRP {
 
   struct DishLocations {
     DishLocations() : total_dish_count_() {}
-    unsigned total_dish_count_;
+    unsigned total_dish_count_;        // customers at all tables with this dish
     std::list<unsigned> table_counts_; // list<> gives O(1) deletion and insertion, which we want
+                                       // .size() is the number of tables for this dish
   };
 
   void Print(std::ostream* out) const {