access_PQ_centroids.ipynb

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   "source": [
    "import faiss\n",
    "import numpy as np\n",
    "\n",
    "feat = np.random.normal(loc=0.0, scale=1.0, size=(10000,512))\n",
    "feat = feat.astype(np.float32)\n",
    "M = 32\n",
    "index = faiss.IndexPQ(d,M,4)\n",
    "index.train(feat)\n",
    "# get the PQ \n",
    "pq = index.pq"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 33,
   "metadata": {},
   "outputs": [],
   "source": [
    "# read the PQ centroids\n",
    "cen = faiss.vector_to_array(pq.centroids)\n",
    "cen = cen.reshape(pq.M, pq.ksub, pq.dsub)"
   ]
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   "cell_type": "code",
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     "data": {
      "text/plain": [
       "(32, 16, 16)"
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     "execution_count": 34,
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   "source": [
    "cen.shape"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 35,
   "metadata": {},
   "outputs": [],
   "source": [
    "# change the centroids of one of the sub-quantizers\n",
    "cen[5, :, :] = 0"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 36,
   "metadata": {},
   "outputs": [],
   "source": [
    "# write back all centroids \n",
    "faiss.copy_array_to_vector(cen.ravel(), index.pq.centroids)"
   ]
  }
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