A matrix diagram shows the relationships between two concept. (Ex. project objective, methods, results, causes, people, etc), help prioritize resources and processes, and organize data.
You would use the matrix diagram to discover the strength of relationships between a grid of rows and columns. A great example of this is the House of Quality in a Quality Functional Design (QFD).
Types of Matrix Diagrams
Use x and y axis.
2 elements on the Y axis. One element on the x axis that splits the y.
2 elements on the Y, 2 elements on the X
a 3-Dimensional grid where there are (2) L-Type matrices joined at the Y axis.