File IndexLSH.h

namespace faiss

Copyright (c) Facebook, Inc. and its affiliates.

This source code is licensed under the MIT license found in the LICENSE file in the root directory of this source tree.

Throughout the library, vectors are provided as float * pointers. Most algorithms can be optimized when several vectors are processed (added/searched) together in a batch. In this case, they are passed in as a matrix. When n vectors of size d are provided as float * x, component j of vector i is

x[ i * d + j ]

where 0 <= i < n and 0 <= j < d. In other words, matrices are always compact. When specifying the size of the matrix, we call it an n*d matrix, which implies a row-major storage.

Copyright (c) Facebook, Inc. and its affiliates.

This source code is licensed under the MIT license found in the LICENSE file in the root directory of this source tree. I/O functions can read/write to a filename, a file handle or to an object that abstracts the medium.

The read functions return objects that should be deallocated with delete. All references within these objectes are owned by the object.

Copyright (c) Facebook, Inc. and its affiliates.

This source code is licensed under the MIT license found in the LICENSE file in the root directory of this source tree. Definition of inverted lists + a few common classes that implement the interface.

Copyright (c) Facebook, Inc. and its affiliates.

This source code is licensed under the MIT license found in the LICENSE file in the root directory of this source tree. Since IVF (inverted file) indexes are of so much use for large-scale use cases, we group a few functions related to them in this small library. Most functions work both on IndexIVFs and IndexIVFs embedded within an IndexPreTransform.

Copyright (c) Facebook, Inc. and its affiliates.

This source code is licensed under the MIT license found in the LICENSE file in the root directory of this source tree. In this file are the implementations of extra metrics beyond L2 and inner product

Copyright (c) Facebook, Inc. and its affiliates.

This source code is licensed under the MIT license found in the LICENSE file in the root directory of this source tree. Defines a few objects that apply transformations to a set of vectors Often these are pre-processing steps.

struct IndexLSH : public faiss::Index
#include <IndexLSH.h>

The sign of each vector component is put in a binary signature

Public Types

typedef unsigned char uint8_t

Public Functions

IndexLSH(idx_t d, int nbits, bool rotate_data = true, bool train_thresholds = false)
const float *apply_preprocess(idx_t n, const float *x) const

Preprocesses and resizes the input to the size required to binarize the data

Parameters

x – input vectors, size n * d

Returns

output vectors, size n * bits. May be the same pointer as x, otherwise it should be deleted by the caller

virtual void train(idx_t n, const float *x) override

Perform training on a representative set of vectors

Parameters
  • n – nb of training vectors

  • x – training vecors, size n * d

virtual void add(idx_t n, const float *x) override

Add n vectors of dimension d to the index.

Vectors are implicitly assigned labels ntotal .. ntotal + n - 1 This function slices the input vectors in chunks smaller than blocksize_add and calls add_core.

Parameters

x – input matrix, size n * d

virtual void search(idx_t n, const float *x, idx_t k, float *distances, idx_t *labels) const override

query n vectors of dimension d to the index.

return at most k vectors. If there are not enough results for a query, the result array is padded with -1s.

Parameters
  • x – input vectors to search, size n * d

  • labels – output labels of the NNs, size n*k

  • distances – output pairwise distances, size n*k

virtual void reset() override

removes all elements from the database.

void transfer_thresholds(LinearTransform *vt)

transfer the thresholds to a pre-processing stage (and unset train_thresholds)

inline ~IndexLSH() override
IndexLSH()
virtual size_t sa_code_size() const override

size of the produced codes in bytes

void sa_encode(idx_t n, const float *x, uint8_t *bytes) const override
void sa_decode(idx_t n, const uint8_t *bytes, float *x) const override

Public Members

int nbits

nb of bits per vector

int bytes_per_vec

nb of 8-bits per encoded vector

bool rotate_data

whether to apply a random rotation to input

bool train_thresholds

whether we train thresholds or use 0

RandomRotationMatrix rrot

optional random rotation

std::vector<float> thresholds

thresholds to compare with

std::vector<uint8_t> codes

encoded dataset