comparison multiprobe.h @ 516:2a7bad47a4a7 multiprobeLSH

New branch to implement multiprobe LSH. Copy of trunk:802. Added multiprobe.{cpp,h} source files.

+/*
+ * MultiProbe C++ class
+ *
+ * Given a LSH structure, perform lookup by probing nearby hash-function locations
+ *
+ * Implementation using C++ STL
+ *
+ * Reference:
+ * Qin Lv, William Josephson, Zhe Wang, Moses Charikar and Kai Li,
+ * "Multi-Probe LSH: Efficient Indexing for High-Dimensional Similarity
+ * Search", Proc. Intl. Conf. VLDB, 2007
+ *
+ *
+ * Copyright (C) 2009 Michael Casey, Dartmouth College, All Rights Reserved
+ * License: GNU Public License 2.0
+ *
+ */
+
+#include <functional>
+#include <queue>
+#include <vector>
+#include <set>
+
+using namespace std ;
+
+typedef set<int > perturbation_set ;
+typedef vector<perturbation_set > vector_of_perturbation_set ;
+typedef pair<perturbation_set, float > min_heap_element ;
+typedef vector<min_heap_element > vector_of_min_heap_element ;
+typedef priority_queue<
+  min_heap_element, 
+  vector_of_min_heap_element, 
+  greater<min_heap_element> 
+  > min_heap_of_perturbation_set ;
+typedef pair<double, pair<int, int> > sorted_distance_functions ;
+
+bool operator>(const min_heap_element& a, const min_heap_element& b){
+  return a.second > b.second;
+}
+
+bool operator<(const min_heap_element& a, const min_heap_element& b){
+  return a.second < b.second;
+}
+
+bool operator>(const sorted_distance_functions& a, const sorted_distance_functions& b){
+  return a.second > b.second;
+}
+
+bool operator<(const sorted_distance_functions& a, const sorted_distance_functions& b){
+  return a.second < b.second;
+}
+
+class MultiProbe{
+protected:
+  min_heap_of_perturbation_set* minHeap;
+  vector_of_perturbation_set* outSets;
+  sorted_distance_functions distFuns;
+public: 
+  MultiProbe();
+  ~MultiProbe();
+
+  // perturbation set operations
+  perturbation_set& shift(perturbation_set);
+  perturbation_set& expand(perturbation_set);
+  double score(perturbation_set&);
+  bool valid(perturbation_set&);
+
+  // generation of perturbation sets
+  void generatePerturbationSets(int, vector<int>&);
+  sorted_distance_functions& makeSortedDistFuns(vector<int> &);
+};
+
+/* NOTES:
+
+Reference:
+Qin Lv, William Josephson, Zhe Wang, Moses Charikar and Kai Li,
+"Multi-Probe LSH: Efficient Indexing for High-Dimensional Similarity
+Search", Proc. Intl. Conf. VLDB, 2007
+
+  i = 1..M (number of hash functions used)
+  f_i(q) = a_i * q + b_i // projection to real line
+  h_i(q) = floor( ( a_i * q + b_i ) / w ) // hash slot  
+  delta \in {-1, +1}
+  x_i( delta ) = distance of query to left or right boundary
+  Delta = [delta_1 delta_2 ... delta_M]
+  score(Delta) = sum_{i=1}_M x_i(delta_i).^2
+  
+  z = sort(x(delta_i), increasing) // i = 1..2M delta={+1,-1}
+  p_j = (i, delta) if z_j == x_i(delta) 
+  
+  A_k is index into p_j
+
+  Multi-probe algorithm (after Lv et al. 2007)
+  ---------------------------------------------
+
+  A0 = {1}
+  minHeap.insert(A0, score(A0))
+  
+  for i = 1 to T do   // T = number of perturbation sets
+     repeat
+        Ai = minHeap.extractMin()
+	As = shift(Ai)
+	minHeap.insert(As, score(As))
+	Ae = expand(Ai)
+	minHeap.insert(Ae, score(Ae))
+     until valid(Ai)
+     output Ai
+  end for
+
+ */