This function takes in a plan of study network and constructs the "core collapse sequence." The core collapse sequence progressively removes courses from the plan of study with increasing prereq counts and calculates the proportion of courses deleted at each step. The process stops when all of the vertices have been removed. A sequence that decreases quickly to zero typically indicates that the network is generally uniform with its prereqs. A sequence with more erratic values that does not settle to zero smoothly would imply more dense sets of prereqs.
core_collapse(plan_of_study)List of two items: (1) sequence - the core collapse sequence, (2) the associated network for each entry
igraph object - An igraph object created using the create_plan_of_study function