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faiss::IndexIVF Struct Referenceabstract

`#include <IndexIVF.h>`

Inheritance diagram for faiss::IndexIVF:

## Public Member Functions
| 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 | train_residual (idx_t n, const float *x)
virtual 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 =0
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
virtual void | reconstruct_from_offset (long list_no, long offset, float *recons) const
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 | add_with_ids (idx_t n, const float *x, const long *xids)
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
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

Index based on a inverted file (IVF)

In the inverted file, the quantizer (an Index instance) provides a quantization index for each vector to be added. The quantization index maps to a list (aka inverted list or posting list), where the id of the vector is then stored.

At search time, the vector to be searched is also quantized, and only the list corresponding to the quantization index is searched. This speeds up the search by making it non-exhaustive. This can be relaxed using multi-probe search: a few (nprobe) quantization indices are selected and several inverted lists are visited.

Sub-classes implement a post-filtering of the index that refines the distance estimation from the query to databse vectors.

Definition at line 77 of file IndexIVF.h.

## Constructor & Destructor Documentation

faiss::IndexIVF::IndexIVF | ( | Index * | quantizer,
|  | size_t | d,
|  | size_t | nlist,
|  | MetricType | metric = `METRIC_L2`
| ) |  |

The Inverted file takes a quantizer (an Index) on input, which implements the function mapping a vector to a list identifier. The pointer is borrowed: the quantizer should not be deleted while the IndexIVF is in use.

Definition at line 106 of file IndexIVF.cpp.

## Member Function Documentation

void faiss::IndexIVF::copy_subset_to | ( | IndexIVF & | other,
|  | int | subset_type,
|  | long | a1,
|  | long | a2
| ) |  | const
| virtual

copy a subset of the entries index to the other index

if subset_type == 0: copies ids in [a1, a2) if subset_type == 1: copies ids if id % a1 == a2 if subset_type == 2: copies inverted lists such that a1 elements are left before and a2 elements are after

Definition at line 375 of file IndexIVF.cpp.

void faiss::IndexIVF::make_direct_map | ( | bool | new_maintain_direct_map = `true` | ) |

intialize a direct map

Parameters

  new_maintain_direct_map | if true, create a direct map, else clear it

Definition at line 139 of file IndexIVF.cpp.

void faiss::IndexIVF::merge_from | ( | IndexIVF & | other,
|  | idx_t | add_id
| ) |  |
| virtual

moves the entries from another dataset to self. On output, other is empty. add_id is added to all moved ids (for sequential ids, this would be this->ntotal

Reimplemented in faiss::IndexIVFPQR.

Definition at line 348 of file IndexIVF.cpp.

void faiss::IndexIVF::reconstruct | ( | idx_t | key,
|  | float * | recons
| ) |  | const
| override virtual

Reconstruct a stored vector (or an approximation if lossy coding)

this function may not be defined for some indexes

Parameters

  key | id of the vector to reconstruct
  recons | reconstucted vector (size d)

Reimplemented from faiss::Index.

Definition at line 180 of file IndexIVF.cpp.

void faiss::IndexIVF::reconstruct_from_offset | ( | long | list_no,
|  | long | offset,
|  | float * | recons
| ) |  | const
| 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 in faiss::IndexIVFFlat, faiss::IndexIVFPQR, faiss::IndexIVFScalarQuantizer, and faiss::IndexIVFPQ.

Definition at line 246 of file IndexIVF.cpp.

void faiss::IndexIVF::reconstruct_n | ( | idx_t | i0,
|  | idx_t | ni,
|  | float * | recons
| ) |  | const
| override virtual

Reconstruct a subset of the indexed vectors.

Overrides default implementation to bypass reconstruct() which requires direct_map to be maintained.

Parameters

  i0 | first vector to reconstruct
  ni | nb of vectors to reconstruct
  recons | output array of reconstructed vectors, size ni * d

Reimplemented from faiss::Index.

Definition at line 190 of file IndexIVF.cpp.

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

assign the vectors, then call search_preassign

Implements faiss::Index.

Definition at line 164 of file IndexIVF.cpp.

void faiss::IndexIVF::search_and_reconstruct | ( | idx_t | n,
|  | const float * | x,
|  | idx_t | k,
|  | float * | distances,
|  | idx_t * | labels,
|  | float * | recons
| ) |  | const
| override virtual

Similar to search, but also reconstructs the stored vectors (or an approximation in the case of lossy coding) for the search results.

Overrides default implementation to avoid having to maintain direct_map and instead fetch the code offsets through the `store_pairs` flag in search_preassigned().

Parameters

  recons | reconstructed vectors size (n, k, d)

Reimplemented from faiss::Index.

Definition at line 210 of file IndexIVF.cpp.

virtual void faiss::IndexIVF::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
| pure 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).

Implemented in faiss::IndexIVFFlat, faiss::IndexIVFPQCompact, faiss::IndexIVFPQR, faiss::IndexIVFScalarQuantizer, and faiss::IndexIVFPQ.

void faiss::IndexIVF::train_residual | ( | idx_t | n,
|  | const float * | x
| ) |  |
| virtual

Sub-classes that encode the residuals can train their encoders here does nothing by default

Reimplemented in faiss::IndexIVFPQR, faiss::IndexIVFScalarQuantizer, and faiss::IndexIVFPQ.

Definition at line 311 of file IndexIVF.cpp.

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

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