Some network data sets are created or received in the form of a matrix.
A matrix can be directed or undirected. In this example, we will import a directed network.
First open a blank NodeXL template.
Next open the matrix workbook in the same instance of Excel (just drag it into the title bar of the current NodeXL Excel instance).
Here is a simple asymmetric matrix with weights for tie strengths.

To import this matrix, switch back to NodeXL and select the Data>Import>From Open Matrix Workbook:

A matrix may or may not have labels (row and column headers) and the user should define what their data set looks like.
The matrix may represent a directed or undirected network (if it is undirected the matrix must be symmetrical!).
This results in data appearing in the Edges worksheet of NodeXL:

This can then be visualized as a network where the edge weights are used to set the thickness of the lines connecting two nodes:
