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#ifndef _CRP_TABLE_MANAGER_H_
#define _CRP_TABLE_MANAGER_H_
#include <iostream>
#include "sparse_vector.h"
#include "sampler.h"
// these are helper classes for implementing token-based CRP samplers
// basically the data structures recommended by Blunsom et al. in the Note.
struct CRPHistogram {
//typedef std::map<unsigned, unsigned> MAPTYPE;
typedef SparseVector<unsigned> MAPTYPE;
typedef MAPTYPE::const_iterator const_iterator;
inline void increment(unsigned bin, unsigned delta = 1u) {
data[bin] += delta;
}
inline void decrement(unsigned bin, unsigned delta = 1u) {
unsigned r = data[bin] -= delta;
if (!r) data.erase(bin);
}
inline void move(unsigned from_bin, unsigned to_bin, unsigned delta = 1u) {
decrement(from_bin, delta);
increment(to_bin, delta);
}
inline const_iterator begin() const { return data.begin(); }
inline const_iterator end() const { return data.end(); }
private:
MAPTYPE data;
};
// A CRPTableManager tracks statistics about all customers
// and tables serving some dish in a CRP and can correctly sample what
// table to remove a customer from and what table to join
struct CRPTableManager {
CRPTableManager() : customers(), tables() {}
inline unsigned num_tables() const {
return tables;
}
inline unsigned num_customers() const {
return customers;
}
inline void create_table() {
h.increment(1);
++tables;
++customers;
}
// seat a customer at a table proportional to the number of customers seated at a table, less the discount
// *new tables are never created by this function!
inline void share_table(const double discount, MT19937* rng) {
const double z = customers - discount * num_tables();
double r = z * rng->next();
const CRPHistogram::const_iterator end = h.end();
CRPHistogram::const_iterator it = h.begin();
for (; it != end; ++it) {
// it->first = number of customers at table
// it->second = number of such tables
double thresh = (it->first - discount) * it->second;
if (thresh > r) break;
r -= thresh;
}
h.move(it->first, it->first + 1);
++customers;
}
// randomly sample a customer
// *tables may be removed
// returns -1 if a table is removed, 0 otherwise
inline int remove_customer(MT19937* rng) {
int r = rng->next() * num_customers();
const CRPHistogram::const_iterator end = h.end();
CRPHistogram::const_iterator it = h.begin();
for (; it != end; ++it) {
int thresh = it->first * it->second;
if (thresh > r) break;
r -= thresh;
}
--customers;
const unsigned tc = it->first;
if (tc == 1) {
h.decrement(1);
--tables;
return -1;
} else {
h.move(tc, tc - 1);
return 0;
}
}
unsigned customers;
unsigned tables;
CRPHistogram h;
};
std::ostream& operator<<(std::ostream& os, const CRPTableManager& tm) {
os << '[' << tm.num_customers() << " total customers at " << tm.num_tables() << " tables ||| ";
for (CRPHistogram::const_iterator it = tm.h.begin(); it != tm.h.end(); ++it) {
if (it != tm.h.begin()) os << " -- ";
os << '(' << it->first << ") x " << it->second;
}
return os << ']';
}
#endif
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