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Why this unit has no video
The document on relations and functions is almost entirely about definitions.
Binary relations, domain, co-domain, "on", "onto", "one-to-one", range, image, functions (2 versions), total and partial (relations and functions), surjective, injective, bijective.
To make things worse, there exist different versions of some definitions, and some terms are used to mean different things, depending on the source.
The document could have continued the endless march of definitions (e.g., inverse, composition, reflexive, irreflexive, symmetric, antisymmetric, etc.)
A video on this material would essentially consist of me reading off the slides. There's not much more to say besides listing various definitions.
Of course, the document (and video) could have been much longer, including many examples of these concepts, but that's not the direction that this course is taking. Some courses have lengthy homework assignments asking to prove or disprove things like whether some relation is antisymmetric or not. I think that's somewhat tedious and we need to focus on other things instead. That's why this topic has such a short document.
All of these concepts do eventually come up if you take certain more advanced mathematics courses. But to prepare for a standard CS degree, and more particularly to prepare for a standard Algorithms course, there is no real need to suffer through memorization of all these definitions at this point in time. My own Algorithms course doesn't use these terms at all, except that functions such as f(n) = n2 are used. But I can't imagine that you've come this far without having seen a function like that already. What you don't need (in Algo) is to think about functions as particular types of relations, that are defined as sets of ordered pairs, etc, which is exactly how these things are introduced in discrete math.
One thing that you must understand is that a function maps types of items to other types of items. It's like a machine, where you feed in something and it faithfully produces something predictable depending on what it was fed. For example it takes integers as input and produces (squared) integers. For a well defined function every "input" cannot map to two "outputs" (that's what predictable means). I assume that you have seen these things before. If not, please post something in EdStem (anonymously if you prefer).
In fact we're going to talk about functions in this course, soon. Specifically we will look at big-O notation, and then recursive functions (i.e., recurrences). I believe that we can cover those topics without the formalities in the pdf on relations.
Conclusion: Use the pdf document on relations and functions as a reference. Take a little bit of time to understand that these concepts and terms exist. If there comes a time in your career when you'll start needing these terms (i.e., definitions), you'll recall where to find them.