faiss/tutorial/cpp/1-Flat.cpp

/*
 * 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.
 */

#include <cstdio>
#include <cstdlib>
#include <random>

#include <faiss/IndexFlat.h>

// 64-bit int
using idx_t = faiss::idx_t;

int main() {
    int d = 64;      // dimension
    int nb = 100000; // database size
    int nq = 10000;  // nb of queries

    std::mt19937 rng;
    std::uniform_real_distribution<> distrib;

    float* xb = new float[d * nb];
    float* xq = new float[d * nq];

    for (int i = 0; i < nb; i++) {
        for (int j = 0; j < d; j++)
            xb[d * i + j] = distrib(rng);
        xb[d * i] += i / 1000.;
    }

    for (int i = 0; i < nq; i++) {
        for (int j = 0; j < d; j++)
            xq[d * i + j] = distrib(rng);
        xq[d * i] += i / 1000.;
    }

    faiss::IndexFlatL2 index(d); // call constructor
    printf("is_trained = %s\n", index.is_trained ? "true" : "false");
    index.add(nb, xb); // add vectors to the index
    printf("ntotal = %zd\n", index.ntotal);

    int k = 4;

    { // sanity check: search 5 first vectors of xb
        idx_t* I = new idx_t[k * 5];
        float* D = new float[k * 5];

        index.search(5, xb, k, D, I);

        // print results
        printf("I=\n");
        for (int i = 0; i < 5; i++) {
            for (int j = 0; j < k; j++)
                printf("%5zd ", I[i * k + j]);
            printf("\n");
        }

        printf("D=\n");
        for (int i = 0; i < 5; i++) {
            for (int j = 0; j < k; j++)
                printf("%7g ", D[i * k + j]);
            printf("\n");
        }

        delete[] I;
        delete[] D;
    }

    { // search xq
        idx_t* I = new idx_t[k * nq];
        float* D = new float[k * nq];

        index.search(nq, xq, k, D, I);

        // print results
        printf("I (5 first results)=\n");
        for (int i = 0; i < 5; i++) {
            for (int j = 0; j < k; j++)
                printf("%5zd ", I[i * k + j]);
            printf("\n");
        }

        printf("D (5 last results)=\n");
        for (int i = nq - 5; i < nq; i++) {
            for (int j = 0; j < k; j++)
                printf("%5f ", D[i * k + j]);
            printf("\n");
        }

        delete[] I;
        delete[] D;
    }

    delete[] xb;
    delete[] xq;

    return 0;
}