"The mathematician's patterns, like the painter's or the poet's must be beautiful; the ideas like the colours or the words, must fit together in a harmonious way."
― G.H. Hardy, A Mathematician's Apology
1/4
We have not yet defined a group. Rather, we are exploring the intuition of them via symmetries. This will *motivate the axioms*, rather than the other way around.
What properties does this group have what might not hold more generally?
2/4
For further insight, consider the symmetries of a triangle. This motivates the idea of relations, and why this "group calculator" tool is useful.
I got so many really good questions and comments in class today. How often does that happen on *Day 1* of abstract algebra??
3/4
Finally, we ended with a Cayley diagram using a different set of generators. (Henceforth, bi-directed arrows will be un-directed).
From a distance, these don't look like the same group. But they are! Surprised? And that's a wrap!
Questions & comments welcome!
4/4
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Happy New Year #MathTwitter! Let's start 2022 w/ Part 1 of a fun series: "Groups you Never Knew Existed...and others you can't POSSIBLY live without!"
Today we'll see the "diquaternions", a term you've never heard of b/c I made it up last month. Let's dig in! 🧵👇
1/17
We'll start with the familiar quaternion group Q_8. Shown here are several Cayley diagrams, a Cayley table, cycle diagram, subgroup lattice, its partition by conjugacy classes, and an action diagram of Aut(Q_8). Each of these highlights different structural features.
2/17
Next, have you ever wondered what would happen if you replace i=e^{2\pi i/4} in Q_8 with a larger root of unity?
These are the dicyclic groups. Here is Dic_6, for n=6. Note that n=4 gives Q_8.
The last two pictures highlight the orbit structure (cyclic subgroups).