# Copyright (c) Meta Platforms, Inc. and affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.

import faiss
import numpy as np

d = 64                           # dimension
nb = 100000                      # database size
nq = 10000                       # nb of queries
np.random.seed(1234)             # make reproducible
xb = np.random.random((nb, d)).astype('float32')    # 64-dim *nb queries
xb[:, 0] += np.arange(nb) / 1000.
xq = np.random.random((nq, d)).astype('float32')
xq[:, 0] += np.arange(nq) / 1000.

m = 8   # 8 specifies that the number of sub-vector is 8
k = 4  # number of dimension in extracted vector
n_bit = 4   # 4 specifies that each sub-vector is encoded as 4 bits
bbs = 32    # build block size ( bbs % 32 == 0 ) for PQ
index = faiss.IndexPQFastScan(d, m, n_bit, faiss.METRIC_L2, bbs)
# construct FastScan Index

assert not index.is_trained
index.train(xb)     # Train vectors data index within mockup database
assert index.is_trained

index.add(xb)
D, I = index.search(xb[:5], k)  # sanity check
print(I)
print(D)
index.nprobe = 10              # make comparable with experiment above
D, I = index.search(xq, k)     # search
print(I[-5:])               # neighbors of the 5 last queries
