Question: Struggling to understand a line of code

I am providing analysis for a Graph I have made using the GraphTheory kit. I am attempting to find a way to find the Betweeness Centrality. So far I have only found one example of the code which is being used to find the Betweeness Centrality of a Network found in a pdf (Attatched below). I have been able to alter the code accordingly to my data but the last line requires some further understanding of how Matrices work in Maple. This is the line I fail to understand completely:

"""""""" BetweenessCentrality_data := < node_data[1.., 1] | < seq(add (ad_mat[i, j] * wt_mat[i, j], j = 1.. num_characters), i = 1. . num_characters)> >: BetweenessCentrality_sorted := FlipDimension( x[2])))>, 1)  """"""""

And this is all the code leading up to the line in question:

"""""""" data := FileTools:-JoinPath(["Excel", "Inter station database (2).xls"], base = datadir);

M := ExcelTools:-Import(data, "Hoja2");

edge_data := Matrix(727, 3, (i, j) --> M[i, j+2] );

with(ListTools);

node_data := Matrix(727, 2, (i, j) -->M[i, j+2] );

convert(Matrix(<<node_data>>), list);

listednode_data := convert(Matrix(<<node_data>>), list);

MakeUnique(listednode_data);

UniqueListedNode_data := MakeUnique(listednode_data);

node_data := Matrix(numelems(UniqueListedNode_data), 1, (i, j) -->UniqueListedNode_data[i]);
 

num_edges := RowDimension(edge_data);
 

num_characters := RowDimension(node_data);
 

G := Graph(node_data[() .. (), 1], weighted);
 

for i from 1 to num_edges do

AddEdge(G, [{edge_data[i, 1], edge_data[i, 2]}, edge_data[i, 3]])

end do;

wt_mat := WeightMatrix(G);
ad_mat := AdjacencyMatrix(G); """"""""

To provide further context, my graph is strongly connected.

If anyone could kindly provide a breakdown of the line of code in question, It would be very appreciated. 

Here is the link to the pdf I used as source for my code:https://www.maplesoft.com/applications/view.aspx?SID=154530