Re:Category Theory for the Working Hacker [video]
by catnaroek on Sunday October 23, 2016 @02:12AM
(#12772246)
Some examples of categories whose arrows aren't functions:
(0) Any monoid can be viewed as a category with a single object. The arrows from the object to itself are the monoid's elements.
(1) Any preorder can be viewed as a category such that, between any two objects, there is at most one arrow, precisely when the source is less or equal than the target.
(2) Given a directed graph, or more generally a quiver[0], there is a small category[1] whose objects are the quiver's nodes, and whose arrows are the paths (finite sequences of edges) from a source node to a target node.
(0) Any monoid can be viewed as a category with a single object. The arrows from the object to itself are the monoid's elements.
(1) Any preorder can be viewed as a category such that, between any two objects, there is at most one arrow, precisely when the source is less or equal than the target.
(2) Given a directed graph, or more generally a quiver[0], there is a small category[1] whose objects are the quiver's nodes, and whose arrows are the paths (finite sequences of edges) from a source node to a target node.
[0] https://en.wikipedia.org/wiki/Quiver_(mathematics)
[1] https://en.wikipedia.org/wiki/Free_category