1. spherical的作用

2. maxpointsper_centroid说明

   根据官方文档GPU k means example所述
   该值设置了256的默认值，对某些大数据集来说需要更改为
   ((numVecsToCluster + numberOfClusters - 1) / numberOfClusters)

     // By default faiss only samples 256 vectors per centroid, in case
     // you are asking for too few centroids for too many vectors.
     // e.g., numberOfClusters = 1000, numVecsToCluster = 1000000 would
     // only sample 256000 vectors.
     //
     // You can override this to use any number of clusters
     // cp.max_points_per_centroid =
     //   ((numVecsToCluster + numberOfClusters - 1) / numberOfClusters);
   

   在python版faiss更改该值的方法

kmeans = faiss.Kmeans(648, 1024, 20, True)
kmeans.cp.max_points_per_centroid = 2560

4. 3