# Update since the update

The last time I posted something meaningful here (not counting the 2014 year-in-review and the most recent claim of attempting necromancy), it was June 2014 and I was about to embark on a summer of traveling. Around that same time, my son was 21 months old, I was working part-time at Wolfram, and I was a pre-doctoral candidate whose academic situation had gone (apparently without being blogged about) from two doctoral advisors with two separate projects to a single advisor plus a second non-advisor faculty colleague.

Typing that out makes me realize how much has changed.

For those of you keeping score, it’s now August 2015, and 13 months after the last update, lots and lots of things have changed. For example, my son is now one month away from being three years old. There’s also a lot of professional stuff, too. Let’s go somewhat chronologically.

• I spent summer 2014 traveling.
• Afterwards, I was offered a full-time position at Wolfram as Math Content Developer. I accepted and took the year off from teaching.
• I landed a lead role in a really awesome math-related project at Wolfram.
• I went to a great conference at Yale and really enjoyed New England. New Haven is absolutely incredible.
• I passed my advanced topics exam (ATE) and became a doctoral candidate. My work was on Gabai’s colossal (first) work on Reebless foliations in 3-manifolds, and while I definitely learned more significant math than I’ve ever learned, I feel like there’s so much in that paper than I’m years away from understanding.
• I went to the Tech Topology Conference soon after becoming a candidate.
• Not long after, FSU had a pretty gnarly conference on Clifford analysis.
• I flew up to Baltimore to interview for an NSA gig. I didn’t get chosen.
• I went to the 40th annual spring lecture series at the University of Arkansas and had a complete blast. I ended up slipping on ice, busting my ankle up pretty badly, and having some travel woes near the end but when all was said and done, I met some cool people (Benson Farb, Allen Hatcher) and saw some really great talks. Oh, and great coffee!
• I went to Rhode Island College and gave an invited lecture on limit sets and computer visualization. It was an honor and I couldn’t have hoped for a better first invited lecture experience.
• I finished a pretty uneventful spring semester at FSU. Lots of work. Lots and lots of work.
• Once summer (2015) rolled around, I got accepted to some pretty great things:
• I was fortunate enough to be awarded a pair of scholarships from the FSU math department.

And now, here we are! It’s officially September 1 (1:07am now): That means Fall semester has started at FSU (which means I’m now a fourth year doctoral student; eek) and things are back in full swing. It never gets familiar, really, no matter how many times it happens. C’est la vie, I guess.

I’ve got a bunch of stuff going on, professionally:

• I’m still trying to make progress on my dissertation research (3-manifolds and, eventually, foliations).
• I’m studying Dirac operators / spin manifolds / hypercomplex structures / supermanifolds / miscellaneous things that seem to get more and more into the realm of theoretical physics as we progress. This is with my non-advisor faculty colleague.
• I’m trying to get a small research project going with an undergraduate at FSU on topological quantum computing (maybe Microsoft will take interest?).

Non-professionally, things have also happened. I got pretty serious into working out for a bit; later, I lost track due to travels, though I’ve since made some pretty considerable body transformations due to a healthier diet. I’ve also tuned back my Wolfram hours to give me more time to do student things; I’ve upgraded my workstations (desktop and mobile); I’ve made the switch from Windows to Linux (full-time rather than as a hobby)…

…that may actually be about it!

So there! Now we’re caught up! That means that I can pick up next time with an actual update / piece of newness / whatever. And who knows – maybe there will even be some math thrown in here! gasp

Good night, everyone.

PS: Oh! I was also introduced to Mnemosyne by a mathematician considerably better than myself! So far, I’m a pretty big fan.

# Random Update, or A Prologue to Travel

Okay, so I’m almost never around these parts anymore. That’s probably obvious to anyone who lands on the home page. Aside from “the random question regarding Hatcher problems” (read: the random pointing out of something very stupid I did when attempting to solve problems from Hatcher), I usually don’t receive many updates regarding this place either.

Truth be told: This place is essentially a wasteland. That makes me at least mildly sad.

I’d like to attempt to remedy that at least somewhat, and in order to attempt such an endeavor, I’ve brainstormed a plan. Before sharing, perhaps I should preface:

I’m about to be traveling quite a bit.

In particular, I’m going to be leaving on Friday (20 June) for approximately five weeks. My travels will include extensive bus rides that will land me in Ithaca, New York, Boston, Massachusetts, and Newark, New Jersey (en route to Staten Island, NY) and will include a variety of math- and computer science-related things.

Much excitement is expected on the professional front.

I figure this makes for at least a somewhat worthwhile opportunity to update this thing, though, since I could use it as a sort of travel diary. Truth be told, I’ve never traveled much, so I don’t know what exactly a travel diary entails; I figure I can come here, vomit out some photos and maybe a video diary or two, and hope that the inspiration I get by being surrounded by greatness will provide me the motivation to at least type up a summary entry or two on some fascinating stuff.

Long story short: Ostensibly, I should be able to post without having to rigorously type up mathematics I’m working on (or attempting to work on). That’s a win.

So yea…I’m at T-minus 51(ish) hours before my first bus departs. There’s lots to do, and so I won’t stick around here much longer. I will try to cough up a legitimate update, though; it’d be silly for me to start a travel diary without at least trying to piece together some sort of update on the journey behind the journey.

In the meantime, I hope this finds the internet in good spirits.

Yours in math,

C

# Hodge Dual part deux

You may recall that I deemed yesterday Differential Geometry Sunday and posted a small expository thing on the Hodge Star/Dual operator. Apparently in my cloudy haze of mathematical mediocrity, I concluded my post without having touched on the derivations I actually intended to touch on.

Sometimes I feel like I need a vacation from my vacation.

In any case, I’m going to take a stab at saying some of the things I’d meant to say yesterday, but in order to ensure we’re all on the same page, I’m going to recall what exactly the Hodge Star/Dual operator is. Then, after the break, I’m going to show some of the cool derivations that come about because of it.

Let $M$ be a manifold of dimension $\dim(M)=n$ and let $\omega=\sum_I f_I dx_I$ be a $k$-form on $M$ for $k\leq n$. Here, $I$ denotes a multi-index which – without loss of generality – can be assumed to be increasing. Then the hodge star operator is the operator which takes $\omega$ to the $(n-k)$-form $*\omega =\sum_I f_I(*dx_I)$ where $*dx_I=\varepsilon_I dx_{I^C}$, where $I^C$ is the multi-index consisting of all numbers $1,\ldots,n$ not in $I$, and where $\varepsilon_I=\pm 1$ denotes the sign of $dx_I dx_{I^C}$.

So what we said is that for the most commonly-recognized example $\mathbb{R}^3$ with orthogonal 1-forms $dx,dy,dz$ and the usual metric $ds^2=dx^2+dy^2+dz^2$, the Hodge Star operator sends $1$ to $dx\wedge dy\wedge dz$ and vice versa, it sends $dx,dy,dz$ to $dy\wedge dz, dz\wedge dx,dx\wedge dy$ respectively, and it sends $(dx\wedge dy)\mapsto dz$, $(dy\wedge dz)\mapsto dx$, and $(dx\wedge dz)\mapsto -dy$. But the question then remains: Why does anybody care?

# Differential Geometry Sunday

I was able to actually stick with my plan a little earlier and spend the day parsing through some stuff in Kobayashi and Nomizu. That’s not a bad way to spend a Sunday.

Somewhere in the middle of that, I ended up stumbling upon something I’d always been somewhat privy to and I did so almost by accident. In the text, I ran across the definition $f_*$ in the following context:

Consider two manifolds $M$ and $M'$ and a mapping $f:M\to M'$ of the prior into the latter. Then for a point $p\in M$, the differential of $f$ at $p$ is a linear mapping $f_*:T_p(M)\to T_{f(p)}(M')$ which is defined as follows: Given a vector $X\in T_p(M)$, choose a path $x(t)$ with $p=x(t_0)$. Then $f_*(X)$ is the vector tangent to the curve $f(x(t))$ at $f(p)=f(x(t_0))$.

The notation reminded me of something I saw during my very first foray into Differential Geometry, namely the Hodge star/dual operator. It was a notion that was so novel when I first saw it that I contemplated preparing a seminar talk at BGSU for my peers, none of whom were geometers of any kind; now that I’ve rediscovered it, I’m having similar ideas for my non-geometer peers here at FSU. But I’m getting ahead of myself…