The document defines a tie-set as a set of branches that form a closed path or loop in a graph containing one link and remaining twigs. A tie-set is also known as a fundamental circuit or f-circuit. The number of tie-sets or loops in a graph equals the number of links. A tie-set matrix describes how branches constitute loops in a graph using an ordered list and reference direction for each loop. Examples of tie-set matrices for different trees are provided.