Understand linkage in dendrogram for regrouping original data points

Hi all,

I have a 516 x 4 matrix X representing 516 data points with 4 observations each. Using hierarchical clustering I group the data points according their relation. I follow the following steps:

T=clusterdata(X,'distance','squaredeuclidean',1);
tree = linkage(T,'ward');
figure, dendrogram(tree)

The first operation creates an array T of size 516 x 1 which assigns a number to each data point including identical numbers for similar data points. Here it is still easy to associate the original data with the cluster results.

Next, from the linkage I get 515 x 3 matrix tree. This matrix has three rows, while the subsequent dendrogram has linkages at several levels within the dendrogram (see attached).

How can I find out from the matrix tree which original data points are lumped together into the various branches of my dendrogram?

Best regards,

Florian

(Matlab 2018b with Statistics & Machine learning toolbox)