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/data/users/matthijs/github_faiss/faiss/IndexPQ.h
1 /**
2 * Copyright (c) 2015-present, Facebook, Inc.
3 * All rights reserved.
4 *
5 * This source code is licensed under the BSD+Patents license found in the
6 * LICENSE file in the root directory of this source tree.
7 */
8
9 // Copyright 2004-present Facebook. All Rights Reserved.
10 // -*- c++ -*-
11
12 #ifndef FAISS_INDEX_PQ_H
13 #define FAISS_INDEX_PQ_H
14
15 #include <stdint.h>
16
17 #include <vector>
18
19 #include "Index.h"
20 #include "ProductQuantizer.h"
21 #include "PolysemousTraining.h"
22
23 namespace faiss {
24
25
26 /** Index based on a product quantizer. Stored vectors are
27 * approximated by PQ codes. */
28 struct IndexPQ: Index {
29
30 /// The product quantizer used to encode the vectors
31 ProductQuantizer pq;
32
33 /// Codes. Size ntotal * pq.code_size
34 std::vector<uint8_t> codes;
35
36 /** Constructor.
37 *
38 * @param d dimensionality of the input vectors
39 * @param M number of subquantizers
40 * @param nbits number of bit per subvector index
41 */
42 IndexPQ (int d, ///< dimensionality of the input vectors
43 size_t M, ///< number of subquantizers
44 size_t nbits, ///< number of bit per subvector index
45 MetricType metric = METRIC_L2);
46
47 IndexPQ ();
48
49 void train(idx_t n, const float* x) override;
50
51 void add(idx_t n, const float* x) override;
52
53 void search(
54 idx_t n,
55 const float* x,
56 idx_t k,
57 float* distances,
58 idx_t* labels) const override;
59
60 void reset() override;
61
62 void reconstruct_n(idx_t i0, idx_t ni, float* recons) const override;
63
64 void reconstruct(idx_t key, float* recons) const override;
65
66 /******************************************************
67 * Polysemous codes implementation
68 ******************************************************/
69 bool do_polysemous_training; ///< false = standard PQ
70
71 /// parameters used for the polysemous training
72 PolysemousTraining polysemous_training;
73
74 /// how to perform the search in search_core
75 enum Search_type_t {
76 ST_PQ, ///< asymmetric product quantizer (default)
77 ST_HE, ///< Hamming distance on codes
78 ST_generalized_HE, ///< nb of same codes
79 ST_SDC, ///< symmetric product quantizer (SDC)
80 ST_polysemous, ///< HE filter (using ht) + PQ combination
81 ST_polysemous_generalize, ///< Filter on generalized Hamming
82 };
83
84 Search_type_t search_type;
85
86 // just encode the sign of the components, instead of using the PQ encoder
87 // used only for the queries
88 bool encode_signs;
89
90 /// Hamming threshold used for polysemy
91 int polysemous_ht;
92
93 // actual polysemous search
94 void search_core_polysemous (idx_t n, const float *x, idx_t k,
95 float *distances, idx_t *labels) const;
96
97 /// prepare query for a polysemous search, but instead of
98 /// computing the result, just get the histogram of Hamming
99 /// distances. May be computed on a provided dataset if xb != NULL
100 /// @param dist_histogram (M * nbits + 1)
101 void hamming_distance_histogram (idx_t n, const float *x,
102 idx_t nb, const float *xb,
103 long *dist_histogram);
104
105 /** compute pairwise distances between queries and database
106 *
107 * @param n nb of query vectors
108 * @param x query vector, size n * d
109 * @param dis output distances, size n * ntotal
110 */
111 void hamming_distance_table (idx_t n, const float *x,
112 int32_t *dis) const;
113
114 };
115
116
117 /// statistics are robust to internal threading, but not if
118 /// IndexPQ::search is called by multiple threads
119 struct IndexPQStats {
120 size_t nq; // nb of queries run
121 size_t ncode; // nb of codes visited
122
123 size_t n_hamming_pass; // nb of passed Hamming distance tests (for polysemy)
124
125 IndexPQStats () {reset (); }
126 void reset ();
127 };
128
129 extern IndexPQStats indexPQ_stats;
130
131
132
133 /** Quantizer where centroids are virtual: they are the Cartesian
134 * product of sub-centroids. */
135 struct MultiIndexQuantizer: Index {
136 ProductQuantizer pq;
137
138 MultiIndexQuantizer (int d, ///< dimension of the input vectors
139 size_t M, ///< number of subquantizers
140 size_t nbits); ///< number of bit per subvector index
141
142 void train(idx_t n, const float* x) override;
143
144 void search(
145 idx_t n,
146 const float* x,
147 idx_t k,
148 float* distances,
149 idx_t* labels) const override;
150
151 /// add and reset will crash at runtime
152 void add(idx_t n, const float* x) override;
153 void reset() override;
154
155 MultiIndexQuantizer () {}
156
157 void reconstruct(idx_t key, float* recons) const override;
158 };
159
160
161 } // namespace faiss
162
163
164
165 #endif
faiss::IndexPQ::codes
std::vector< uint8_t > codes
Codes. Size ntotal * pq.code_size.
Definition: IndexPQ.h:34
faiss::IndexPQStats
Definition: IndexPQ.h:119
faiss::IndexPQ::ST_HE
Hamming distance on codes.
Definition: IndexPQ.h:77
faiss::IndexPQ::do_polysemous_training
bool do_polysemous_training
false = standard PQ
Definition: IndexPQ.h:69
faiss::IndexPQ::train
void train(idx_t n, const float *x) override
Definition: IndexPQ.cpp:54
faiss::MultiIndexQuantizer::reset
void reset() override
removes all elements from the database.
Definition: IndexPQ.cpp:890
faiss::MultiIndexQuantizer::train
void train(idx_t n, const float *x) override
Definition: IndexPQ.cpp:794
faiss::IndexPQ
Definition: IndexPQ.h:28
faiss::Index::d
int d
vector dimension
Definition: Index.h:64
faiss::IndexPQ::hamming_distance_histogram
void hamming_distance_histogram(idx_t n, const float *x, idx_t nb, const float *xb, long *dist_histogram)
Definition: IndexPQ.cpp:382
faiss::IndexPQ::Search_type_t
Search_type_t
how to perform the search in search_core
Definition: IndexPQ.h:75
faiss::IndexPQ::ST_polysemous_generalize
Filter on generalized Hamming.
Definition: IndexPQ.h:81
faiss::Index::idx_t
long idx_t
all indices are this type
Definition: Index.h:62
faiss::IndexPQ::pq
ProductQuantizer pq
The product quantizer used to encode the vectors.
Definition: IndexPQ.h:31
faiss::IndexPQ::add
void add(idx_t n, const float *x) override
Definition: IndexPQ.cpp:78
faiss::IndexPQ::ST_generalized_HE
nb of same codes
Definition: IndexPQ.h:78
faiss::PolysemousTraining
optimizes the order of indices in a ProductQuantizer
Definition: PolysemousTraining.h:125
faiss::IndexPQ::hamming_distance_table
void hamming_distance_table(idx_t n, const float *x, int32_t *dis) const
Definition: IndexPQ.cpp:370
faiss::MultiIndexQuantizer::search
void search(idx_t n, const float *x, idx_t k, float *distances, idx_t *labels) const override
Definition: IndexPQ.cpp:805
faiss::IndexPQ::reconstruct
void reconstruct(idx_t key, float *recons) const override
Definition: IndexPQ.cpp:104
faiss::MultiIndexQuantizer
Definition: IndexPQ.h:135
faiss::Index
Definition: Index.h:60
faiss::IndexPQ::reconstruct_n
void reconstruct_n(idx_t i0, idx_t ni, float *recons) const override
Definition: IndexPQ.cpp:94
faiss::IndexPQ::ST_PQ
asymmetric product quantizer (default)
Definition: IndexPQ.h:76
faiss::MultiIndexQuantizer::reconstruct
void reconstruct(idx_t key, float *recons) const override
Definition: IndexPQ.cpp:861
faiss::IndexPQ::ST_polysemous
HE filter (using ht) + PQ combination.
Definition: IndexPQ.h:80
faiss::ProductQuantizer
Definition: ProductQuantizer.h:25
faiss::MultiIndexQuantizer::add
void add(idx_t n, const float *x) override
add and reset will crash at runtime
Definition: IndexPQ.cpp:884
faiss::IndexPQ::reset
void reset() override
removes all elements from the database.
Definition: IndexPQ.cpp:88
faiss::IndexPQ::search
void search(idx_t n, const float *x, idx_t k, float *distances, idx_t *labels) const override
Definition: IndexPQ.cpp:124
faiss::IndexPQ::ST_SDC
symmetric product quantizer (SDC)
Definition: IndexPQ.h:79
faiss::IndexPQ::polysemous_ht
int polysemous_ht
Hamming threshold used for polysemy.
Definition: IndexPQ.h:91
faiss::IndexPQ::polysemous_training
PolysemousTraining polysemous_training
parameters used for the polysemous training
Definition: IndexPQ.h:72
faiss::MetricType
MetricType
Some algorithms support both an inner product version and a L2 search version.
Definition: Index.h:43