Add IndexIVFPQ example

_example/ivfflat/ivfflat.go

@@ -44,7 +44,6 @@ func main() {
 	index.Train(xb)
 	fmt.Println("IsTrained() =", index.IsTrained())
 	index.Add(xb)
-	fmt.Println("Ntotal() =", index.Ntotal())
 
 	k := int64(4)
 

_example/ivfpq/ivfpq.go

@@ -0,0 +1,95 @@
+// Usage example for IndexIVFPQ.
+// Based on tutorial/cpp/3-IVFPQ.cpp from the Faiss distribution.
+// See https://github.com/facebookresearch/faiss/wiki/Lower-memory-footprint for
+// more information.
+package main
+
+import (
+	"fmt"
+	"log"
+	"math/rand"
+
+	"github.com/DataIntelligenceCrew/go-faiss"
+)
+
+func main() {
+	d := 64      // dimension
+	nb := 100000 // database size
+	nq := 10000  // number of queries
+
+	xb := make([]float32, d*nb)
+	xq := make([]float32, d*nq)
+
+	for i := 0; i < nb; i++ {
+		for j := 0; j < d; j++ {
+			xb[i*d+j] = rand.Float32()
+		}
+		xb[i*d] += float32(i) / 1000
+	}
+
+	for i := 0; i < nq; i++ {
+		for j := 0; j < d; j++ {
+			xq[i*d+j] = rand.Float32()
+		}
+		xq[i*d] += float32(i) / 1000
+	}
+
+	index, err := faiss.IndexFactory(d, "IVF100,PQ8", faiss.MetricL2)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer index.Delete()
+
+	index.Train(xb)
+	index.Add(xb)
+
+	k := int64(4)
+
+	// sanity check
+
+	dist, ids, err := index.Search(xb[:5*d], k)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println("ids=")
+	for i := int64(0); i < 5; i++ {
+		for j := int64(0); j < k; j++ {
+			fmt.Printf("%5d ", ids[i*k+j])
+		}
+		fmt.Println()
+	}
+
+	fmt.Println("dist=")
+	for i := int64(0); i < 5; i++ {
+		for j := int64(0); j < k; j++ {
+			fmt.Printf("%7.6g ", dist[i*k+j])
+		}
+		fmt.Println()
+	}
+
+	// search xq
+
+	ps, err := faiss.NewParameterSpace()
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer ps.Delete()
+
+	if err := ps.SetIndexParameter(index, "nprobe", 10); err != nil {
+		log.Fatal(err)
+	}
+
+	_, ids, err = index.Search(xq, k)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println("ids (last 5 results)=")
+	for i := int64(nq) - 5; i < int64(nq); i++ {
+		for j := int64(0); j < k; j++ {
+			fmt.Printf("%5d ", ids[i*k+j])
+		}
+		fmt.Println()
+	}
+}