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/data/users/matthijs/github_faiss/faiss/Clustering.cpp
1 /**
2 * Copyright (c) 2015-present, Facebook, Inc.
3 * All rights reserved.
4 *
5 * This source code is licensed under the CC-by-NC 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 kmeans clustering routines
11 */
12
13 #include "Clustering.h"
14
15
16
17 #include <cmath>
18 #include <cstdio>
19 #include <cstring>
20
21 #include "utils.h"
22 #include "FaissAssert.h"
23 #include "IndexFlat.h"
24
25 namespace faiss {
26
27 ClusteringParameters::ClusteringParameters ():
28 niter(25),
29 nredo(1),
30 verbose(false), spherical(false),
31 update_index(false),
32 min_points_per_centroid(39),
33 max_points_per_centroid(256),
34 seed(1234)
35 {}
36 // 39 corresponds to 10000 / 256 -> to avoid warnings on PQ tests with randu10k
37
38
39 Clustering::Clustering (int d, int k):
40 d(d), k(k) {}
41
42 Clustering::Clustering (int d, int k, const ClusteringParameters &cp):
43 ClusteringParameters (cp), d(d), k(k) {}
44
45
46
47 static double imbalance_factor (int n, int k, long *assign) {
48 std::vector<int> hist(k, 0);
49 for (int i = 0; i < n; i++)
50 hist[assign[i]]++;
51
52 double tot = 0, uf = 0;
53
54 for (int i = 0 ; i < k ; i++) {
55 tot += hist[i];
56 uf += hist[i] * (double) hist[i];
57 }
58 uf = uf * k / (tot * tot);
59
60 return uf;
61 }
62
63
64
65
66 void Clustering::train (idx_t nx, const float *x_in, Index & index) {
67 FAISS_THROW_IF_NOT_MSG (nx >= k,
68 "need at least as many training points as clusters");
69
70 double t0 = getmillisecs();
71
72 // yes it is the user's responsibility, but it may spare us some
73 // hard-to-debug reports.
74 for (size_t i = 0; i < nx * d; i++) {
75 FAISS_THROW_IF_NOT_MSG (finite (x_in[i]),
76 "input contains NaN's or Inf's");
77 }
78
79 const float *x = x_in;
80 ScopeDeleter<float> del1;
81
82 if (nx > k * max_points_per_centroid) {
83 if (verbose)
84 printf("Sampling a subset of %ld / %ld for training\n",
85 k * max_points_per_centroid, nx);
86 std::vector<int> perm (nx);
87 rand_perm (perm.data (), nx, seed);
88 nx = k * max_points_per_centroid;
89 float * x_new = new float [nx * d];
90 for (idx_t i = 0; i < nx; i++)
91 memcpy (x_new + i * d, x + perm[i] * d, sizeof(x_new[0]) * d);
92 x = x_new;
93 del1.set (x);
94 } else if (nx < k * min_points_per_centroid) {
95 fprintf (stderr,
96 "WARNING clustering %ld points to %ld centroids: "
97 "please provide at least %ld training points\n",
98 nx, k, idx_t(k) * min_points_per_centroid);
99 }
100
101
102 if (verbose)
103 printf("Clustering %d points in %ldD to %ld clusters, "
104 "redo %d times, %d iterations\n",
105 int(nx), d, k, nredo, niter);
106
107
108 idx_t * assign = new idx_t[nx];
109 ScopeDeleter<idx_t> del (assign);
110 float * dis = new float[nx];
111 ScopeDeleter<float> del2(dis);
112
113 float best_err = 1e50;
114 double t_search_tot = 0;
115 if (verbose) {
116 printf(" Preprocessing in %.2f s\n",
117 (getmillisecs() - t0)/1000.);
118 }
119 t0 = getmillisecs();
120
121 for (int redo = 0; redo < nredo; redo++) {
122
123 std::vector<float> buf_centroids;
124
125 std::vector<float> &cur_centroids =
126 nredo == 1 ? centroids : buf_centroids;
127
128 if (verbose && nredo > 1) {
129 printf("Outer iteration %d / %d\n", redo, nredo);
130 }
131
132 if (cur_centroids.size() == 0) {
133 // initialize centroids with random points from the dataset
134 cur_centroids.resize (d * k);
135 std::vector<int> perm (nx);
136
137 rand_perm (perm.data(), nx, seed + 1 + redo * 15486557L);
138 #pragma omp parallel for
139 for (int i = 0; i < k ; i++)
140 memcpy (&cur_centroids[i * d], x + perm[i] * d,
141 d * sizeof (float));
142 } else { // assume user provides some meaningful initialization
143 FAISS_THROW_IF_NOT (cur_centroids.size() == d * k);
144 FAISS_THROW_IF_NOT_MSG (nredo == 1,
145 "will redo with same initialization");
146 }
147
148 if (spherical)
149 fvec_renorm_L2 (d, k, cur_centroids.data());
150
151 if (!index.is_trained)
152 index.train (k, cur_centroids.data());
153
154 FAISS_THROW_IF_NOT (index.ntotal == 0);
155 index.add (k, cur_centroids.data());
156 float err = 0;
157 for (int i = 0; i < niter; i++) {
158 double t0s = getmillisecs();
159 index.search (nx, x, 1, dis, assign);
160 t_search_tot += getmillisecs() - t0s;
161
162 err = 0;
163 for (int j = 0; j < nx; j++)
164 err += dis[j];
165 obj.push_back (err);
166
167 int nsplit = km_update_centroids (x, cur_centroids.data(),
168 assign, d, k, nx);
169
170 if (verbose) {
171 printf (" Iteration %d (%.2f s, search %.2f s): "
172 "objective=%g imbalance=%.3f nsplit=%d \r",
173 i, (getmillisecs() - t0) / 1000.0,
174 t_search_tot / 1000,
175 err, imbalance_factor (nx, k, assign),
176 nsplit);
177 fflush (stdout);
178 }
179
180 if (spherical)
181 fvec_renorm_L2 (d, k, cur_centroids.data());
182
183 index.reset ();
184 if (update_index)
185 index.train (k, cur_centroids.data());
186
187 assert (index.ntotal == 0);
188 index.add (k, cur_centroids.data());
189 }
190 if (verbose) printf("\n");
191 if (nredo > 1) {
192 if (err < best_err) {
193 if (verbose)
194 printf ("Objective improved: keep new clusters\n");
195 centroids = buf_centroids;
196 best_err = err;
197 }
198 index.reset ();
199 }
200 }
201
202 }
203
204 float kmeans_clustering (size_t d, size_t n, size_t k,
205 const float *x,
206 float *centroids)
207 {
208 Clustering clus (d, k);
209 clus.verbose = d * n * k > (1L << 30);
210 // display logs if > 1Gflop per iteration
211 IndexFlatL2 index (d);
212 clus.train (n, x, index);
213 memcpy(centroids, clus.centroids.data(), sizeof(*centroids) * d * k);
214 return clus.obj.back();
215 }
216
217 } // namespace faiss
faiss::ClusteringParameters::niter
int niter
clustering iterations
Definition: Clustering.h:25
faiss::km_update_centroids
int km_update_centroids(const float *x, float *centroids, long *assign, size_t d, size_t k, size_t n)
Definition: utils.cpp:1369
faiss::ClusteringParameters::nredo
int nredo
redo clustering this many times and keep best
Definition: Clustering.h:26
faiss::ClusteringParameters::ClusteringParameters
ClusteringParameters()
sets reasonable defaults
Definition: Clustering.cpp:27
faiss::Index::reset
virtual void reset()=0
removes all elements from the database.
faiss::IndexFlatL2
Definition: IndexFlat.h:79
faiss::Clustering::Clustering
Clustering(int d, int k)
the only mandatory parameters are k and d
Definition: Clustering.cpp:39
faiss::Clustering::k
size_t k
nb of centroids
Definition: Clustering.h:59
faiss::ScopeDeleter
Definition: FaissException.h:39
faiss::ClusteringParameters::seed
int seed
seed for the random number generator
Definition: Clustering.h:35
faiss::ClusteringParameters::min_points_per_centroid
int min_points_per_centroid
otherwise you get a warning
Definition: Clustering.h:32
faiss::Clustering
Definition: Clustering.h:56
faiss::Index::add
virtual void add(idx_t n, const float *x)=0
faiss::Clustering::obj
std::vector< float > obj
Definition: Clustering.h:66
faiss::kmeans_clustering
float kmeans_clustering(size_t d, size_t n, size_t k, const float *x, float *centroids)
Definition: Clustering.cpp:204
faiss::Index::ntotal
idx_t ntotal
total nb of indexed vectors
Definition: Index.h:65
faiss::getmillisecs
double getmillisecs()
ms elapsed since some arbitrary epoch
Definition: utils.cpp:70
faiss::Clustering::centroids
std::vector< float > centroids
centroids (k * d)
Definition: Clustering.h:62
faiss::Clustering::d
size_t d
dimension of the vectors
Definition: Clustering.h:58
faiss::Index::search
virtual void search(idx_t n, const float *x, idx_t k, float *distances, idx_t *labels) const =0
faiss::ClusteringParameters::update_index
bool update_index
update index after each iteration?
Definition: Clustering.h:30
faiss::ClusteringParameters
Definition: Clustering.h:24
faiss::Index
Definition: Index.h:60
faiss::Clustering::train
virtual void train(idx_t n, const float *x, faiss::Index &index)
Index is used during the assignment stage.
Definition: Clustering.cpp:66
faiss::Index::is_trained
bool is_trained
set if the Index does not require training, or if training is done already
Definition: Index.h:69
faiss::Index::train
virtual void train(idx_t n, const float *x)
Definition: Index.h:89
faiss::ClusteringParameters::spherical
bool spherical
do we want normalized centroids?
Definition: Clustering.h:29
faiss::ClusteringParameters::max_points_per_centroid
int max_points_per_centroid
to limit size of dataset
Definition: Clustering.h:33