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faiss::IndexIVFPQ Struct Reference

`#include <IndexIVFPQ.h>`

Inheritance diagram for faiss::IndexIVFPQ:

## Public Member Functions
| IndexIVFPQ (Index *quantizer, size_t d, size_t nlist, size_t M, size_t nbits_per_idx)
void | add_with_ids (idx_t n, const float *x, const long *xids=nullptr) override
void | add_core_o (idx_t n, const float *x, const long *xids, float *residuals_2, const long *precomputed_idx=nullptr)
void | train_residual (idx_t n, const float *x) override
| trains the product quantizer
void | train_residual_o (idx_t n, const float *x, float *residuals_2)
| same as train_residual, also output 2nd level residuals
void | reconstruct_from_offset (long list_no, long offset, float *recons) const override
size_t | find_duplicates (idx_t *ids, size_t *lims) const
void | encode (long key, const float *x, uint8_t *code) const
void | encode_multiple (size_t n, long *keys, const float *x, uint8_t *codes, bool compute_keys=false) const
void | decode_multiple (size_t n, const long *keys, const uint8_t *xcodes, float *x) const
| inverse of encode_multiple
void | search_preassigned (idx_t n, const float *x, idx_t k, const idx_t *assign, const float *centroid_dis, float *distances, idx_t *labels, bool store_pairs) const override
void | precompute_table ()
| build precomputed table More...
Public Member Functions inherited from faiss::IndexIVF
| IndexIVF (Index *quantizer, size_t d, size_t nlist, MetricType metric=METRIC_L2)
void | reset () override
| removes all elements from the database.
void | train (idx_t n, const float *x) override
| Trains the quantizer and calls train_residual to train sub-quantizers.
void | add (idx_t n, const float *x) override
| Quantizes x and calls add_with_key.
virtual void | search (idx_t n, const float *x, idx_t k, float *distances, idx_t *labels) const override
void | reconstruct (idx_t key, float *recons) const override
void | reconstruct_n (idx_t i0, idx_t ni, float *recons) const override
void | search_and_reconstruct (idx_t n, const float *x, idx_t k, float *distances, idx_t *labels, float *recons) const override
long | remove_ids (const IDSelector &sel) override
| Dataset manipulation functions.
virtual void | merge_from (IndexIVF &other, idx_t add_id)
virtual void | copy_subset_to (IndexIVF &other, int subset_type, long a1, long a2) const
size_t | get_list_size (size_t list_no) const
void | make_direct_map (bool new_maintain_direct_map=true)
double | imbalance_factor () const
| 1= perfectly balanced, >1: imbalanced
void | print_stats () const
| display some stats about the inverted lists
Public Member Functions inherited from faiss::Index
| Index (idx_t d=0, MetricType metric=METRIC_L2)
virtual void | range_search (idx_t n, const float *x, float radius, RangeSearchResult *result) const
void | assign (idx_t n, const float *x, idx_t *labels, idx_t k=1)
void | compute_residual (const float *x, float *residual, idx_t key) const
void | display () const
Public Member Functions inherited from faiss::Level1Quantizer
void | train_q1 (size_t n, const float *x, bool verbose, MetricType metric_type)
| Trains the quantizer and calls train_residual to train sub-quantizers.
| Level1Quantizer (Index *quantizer, size_t nlist)

## Public Attributes
bool | by_residual
| Encode residual or plain vector?
int | use_precomputed_table
| if by_residual, build precompute tables
ProductQuantizer | pq
| produces the codes
bool | do_polysemous_training
| reorder PQ centroids after training?
PolysemousTraining * | polysemous_training
| if NULL, use default
size_t | scan_table_threshold
| use table computation or on-the-fly?
int | polysemous_ht
| Hamming thresh for polysemous filtering.
std::vector< float > | precomputed_table
Public Attributes inherited from faiss::IndexIVF
size_t | nprobe
| number of probes at query time
size_t | max_codes
| max nb of codes to visit to do a query
std::vector< std::vector< long > > | ids
| Inverted lists for indexes.
size_t | code_size
| code size per vector in bytes
std::vector< std::vector < uint8_t > > | codes
bool | maintain_direct_map
| map for direct access to the elements. Enables reconstruct().
std::vector< long > | direct_map
Public Attributes inherited from faiss::Index
int | d
| vector dimension
idx_t | ntotal
| total nb of indexed vectors
bool | verbose
| verbosity level
bool | is_trained
| set if the Index does not require training, or if training is done already
MetricType | metric_type
| type of metric this index uses for search
Public Attributes inherited from faiss::Level1Quantizer
Index * | quantizer
| quantizer that maps vectors to inverted lists
size_t | nlist
| number of possible key values
char | quantizer_trains_alone
bool | own_fields
| whether object owns the quantizer
ClusteringParameters | cp
| to override default clustering params
Index * | clustering_index
| to override index used during clustering

## Additional Inherited Members
Public Types inherited from faiss::Index
typedef long | idx_t
| all indices are this type

## Detailed Description

Inverted file with Product Quantizer encoding. Each residual vector is encoded as a product quantizer code.

Definition at line 29 of file IndexIVFPQ.h.

## Member Function Documentation

void faiss::IndexIVFPQ::add_core_o | ( | idx_t | n,
|  | const float * | x,
|  | const long * | xids,
|  | float * | residuals_2,
|  | const long * | precomputed_idx = `nullptr`
| ) |  |

same as add_core, also:

- output 2nd level residuals if residuals_2 != NULL
- use precomputed list numbers if precomputed_idx != NULL

Definition at line 191 of file IndexIVFPQ.cpp.

void faiss::IndexIVFPQ::add_with_ids | ( | idx_t | n,
|  | const float * | x,
|  | const long * | xids = `nullptr`
| ) |  |
| override virtual

Same as add, but stores xids instead of sequential ids.

The default implementation fails with an assertion, as it is not supported by all indexes.

Parameters

  xids | if non-null, ids to store for the vectors (size n)

Reimplemented from faiss::Index.

Reimplemented in faiss::IndexIVFPQR.

Definition at line 185 of file IndexIVFPQ.cpp.

void faiss::IndexIVFPQ::encode_multiple | ( | size_t | n,
|  | long * | keys,
|  | const float * | x,
|  | uint8_t * | codes,
|  | bool | compute_keys = `false`
| ) |  | const

Encode multiple vectors

Parameters

  n | nb vectors to encode
  keys | posting list ids for those vectors (size n)
  x | vectors (size n * d)
  codes | output codes (size n * code_size)
  compute_keys | if false, assume keys are precomputed, otherwise compute them

Definition at line 149 of file IndexIVFPQ.cpp.

size_t faiss::IndexIVFPQ::find_duplicates | ( | idx_t * | ids,
|  | size_t * | lims
| ) |  | const

Find exact duplicates in the dataset.

the duplicates are returned in pre-allocated arrays (see the max sizes).

lims limits between groups of duplicates (max size ntotal / 2 + 1) ids ids[lims[i]] : ids[lims[i+1]-1] is a group of duplicates (max size ntotal)

Returns
  n number of groups found

Definition at line 1044 of file IndexIVFPQ.cpp.

void faiss::IndexIVFPQ::precompute_table | ( |  | ) |

build precomputed table

Precomputed tables for residuals

During IVFPQ search with by_residual, we compute

    d = || x - y_C - y_R ||^2

where x is the query vector, y_C the coarse centroid, y_R the refined PQ centroid. The expression can be decomposed as:

d = || x - y_C ||^2 + || y_R ||^2 + 2 * (y_C|y_R) - 2 * (x|y_R)

term 1 term 2 term 3

When using multiprobe, we use the following decomposition:

- term 1 is the distance to the coarse centroid, that is computed during the 1st stage search.
- term 2 can be precomputed, as it does not involve x. However, because of the PQ, it needs nlist * M * ksub storage. This is why use_precomputed_table is off by default
- term 3 is the classical non-residual distance table.

Since y_R defined by a product quantizer, it is split across subvectors and stored separately for each subvector. If the coarse quantizer is a MultiIndexQuantizer then the table can be stored more compactly.

At search time, the tables for term 2 and term 3 are added up. This is faster when the length of the lists is > ksub * M.

Definition at line 344 of file IndexIVFPQ.cpp.

void faiss::IndexIVFPQ::reconstruct_from_offset | ( | long | list_no,
|  | long | offset,
|  | float * | recons
| ) |  | const
| override virtual

Reconstruct a vector given the location in terms of (inv list index + inv list offset) instead of the id.

Useful for reconstructing when the direct_map is not maintained and the inv list offset is computed by search_preassigned() with `store_pairs` set.

Reimplemented from faiss::IndexIVF.

Reimplemented in faiss::IndexIVFPQR.

Definition at line 291 of file IndexIVFPQ.cpp.

void faiss::IndexIVFPQ::search_preassigned | ( | idx_t | n,
|  | const float * | x,
|  | idx_t | k,
|  | const idx_t * | assign,
|  | const float * | centroid_dis,
|  | float * | distances,
|  | idx_t * | labels,
|  | bool | store_pairs
| ) |  | const
| override virtual

search a set of vectors, that are pre-quantized by the IVF quantizer. Fill in the corresponding heaps with the query results. search() calls this.

Parameters

  n | nb of vectors to query
  x | query vectors, size nx * d
  assign | coarse quantization indices, size nx * nprobe
  centroid_dis | distances to coarse centroids, size nx * nprobe
  distance | output distances, size n * k
  labels | output labels, size n * k
  store_pairs | store inv list index + inv list offset instead in upper/lower 32 bit of result, instead of ids (used for reranking).

Implements faiss::IndexIVF.

Reimplemented in faiss::IndexIVFPQCompact, and faiss::IndexIVFPQR.

Definition at line 919 of file IndexIVFPQ.cpp.

## Member Data Documentation

std::vector<float> faiss::IndexIVFPQ::precomputed_table

if use_precompute_table size nlist * pq.M * pq.ksub

Definition at line 44 of file IndexIVFPQ.h.

The documentation for this struct was generated from the following files:

- /data/users/matthijs/github_faiss/faiss/IndexIVFPQ.h
- /data/users/matthijs/github_faiss/faiss/IndexIVFPQ.cpp