DBindex_BIG: DBindex_BIG
In chickn: 'Compressive' Hierarchical Kernel Clustering Toolbox

Davies Bouldin index computation

DBindex_BIG(
  X_cumsum,
  rowInd,
  Clusters,
  C,
  C_cumsum,
  cluster_size,
  DistInter,
  R
)

`X_cumsum`	is a Filebacked data cummulative sum matrix n x N
`rowInd`	is a vector of the row indeces
`Clusters`	is a list of cluster assignment
`C`	is a matrix of the cluster centroids
`C_cumsum`	is a matrix of the cummulative sums of cluster centroids
`cluster_size`	is a vector of the cluster sizes
`DistInter`	is a matrix of the inter distances
`R`	is a matrix of the intra distances