DendrogramNode

A dendrogram node is a representation of a cluster.

The dendrogram is created using the agglomerative strategy (i.e., a bottom-up approach) based on the following steps:

1. Initially (i.e., at level 0), each node comprises its own cluster. At this point, each node of the original graph (the one that will be clustered) is mapped to one of the dendrogram's leaf nodes.
2. At each step, pairs of clusters are merged while moving up the hierarchy. In this case, a new dendrogram node is created and the corresponding dissimilarity value between the two merged clusters can be obtained using dissimilarityValue. The dissimilarity values are monotonously increasing starting from zero which corresponds to the leaf nodes of the dendrogram.
3. The algorithm continues until all nodes belong to the same cluster. At this point, the root of the dendrogram is reached and can be obtained using dendrogramRoot.

The dendrogram is a binary tree that is directed from the root to the leaves. Moving from a node to its children effectively represents a split of the node's cluster into two smaller clusters. Moving from a child to its parent represents merging the child's cluster with another cluster to form a larger one.

For each node of the dendrogram, it is possible to retrieve the set of nodes of the original graph that belong to this dendrogram node using clusterNodes. Only the leaf nodes of the dendrogram actually represent a node of the original graph. This means that for all other inner nodes of the dendrogram, the original node is null.