iiinova — where your digital self keeps evolving

Rook Bridson @rookbridson.bsky.social · 17/09/2026

oh, no worries, just compute its antiderivative 😄

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Rook Bridson @rookbridson.bsky.social · 07/09/2026

glad to have a job where llm tools are largely irrelevant, at best a distraction

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Rook Bridson @rookbridson.bsky.social · 13/05/2026

Meanwhile, I’m not risking travel to the US for SIGGRAPH in LA 🙃

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Rook Bridson @rookbridson.bsky.social · 11/05/2026

i think of it more as a delightful unending cave of wonders

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Gillian Branstetter @gbbranstetter.bsky.social · 07/05/2026

Everyone read Judith Herman

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Bruno Levy @brunolevy01.bsky.social · 28/04/2026

Preparing for our course "Optimal Transport Based fluid simulation: New and Old" with Cyprien Plateau-Holleville (EUROGRAPHICS and SIGGRAPH) 2D simulation of "droplet hurdles race" (De Maleprade et.al). Features high surface tension, viscosity and fluid boundary - domain interactions.

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Rook Bridson @rookbridson.bsky.social · 26/04/2026

I don’t know if my birthday was too early in the school year or just i was too much an outsider but I never had it happen to me either (and I always had wanted to taste a flakie, but that was Not Approved by my parents)

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Rook Bridson @rookbridson.bsky.social · 10/04/2026

geometric optics from the wave equation! turbulence modeling with RANS and LES et al! homogenization!

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Rook Bridson @rookbridson.bsky.social · 10/04/2026

The second idea here is a natural tie in to a whole lot of amazingly cool applied math — starting from a baseline fine-scale model, approximating its solution in a nonlinear way that abstracts away the fine-scale variations so we can focus on the larger scale behaviour

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Rook Bridson @rookbridson.bsky.social · 09/04/2026

(and for a rigid body now the natural time sampling frequency comes from its angular velocity!), or it could mean modeling the time evolution of the slowly decaying _amplitude_ of the 440Hz vibration (like replacing x(t) with A(t)sin(2 π 440 t) and trying to find a nice ODE for A(t) alone)

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Rook Bridson @rookbridson.bsky.social · 09/04/2026

In a case like this there really are only two choices to do it “right”: either take the *physically* required small time steps (according to Nyquist at least), or change your model. Changing the model in this case could mean e.g. abstracting out all elastic behaviour and making it a rigid body

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Rook Bridson @rookbridson.bsky.social · 09/04/2026

or adjust physical parameters etc. The results you are producing are outputs from a discrete system which is _not_ approximating the continuous physical system you thought you were modeling.

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Rook Bridson @rookbridson.bsky.social · 09/04/2026

And even if you’re happy-ish with the results — probably rapid damping of an oscillation around 30Hz — as somehow being visually representative of the “averaged” behaviour maybe, the results will change unphysically and unintuitively if you adjust the time step (eg occasionally do two substeps),

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Rook Bridson @rookbridson.bsky.social · 09/04/2026

If you want to simulate a 440Hz tuning fork but use time steps of 1/30 s, sorry: you just can’t do that in any useful or meaningful way. If you use Backards Euler with those big steps anyways, you’ll get some kind of solution if the implicit equations are solvable, but it obviously won’t be 440Hz

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Rook Bridson @rookbridson.bsky.social · 09/04/2026

But what if you the user have a hard computational budget and want to take even bigger time steps than that? That in itself does not make the problem “stiff”, and a stiff integrator may fail in bad ways — probably remaining stable, but giving aliased garbage in some sense.

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Rook Bridson @rookbridson.bsky.social · 09/04/2026

Stiffly accurate time integration schemes, such as members of the BDF family, allow you to get an accurate solution only using time steps that resolve the solution (in signal processing terms, at a sampling frequency high enough to avoid aliasing)

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Rook Bridson @rookbridson.bsky.social · 09/04/2026

A stiff problem is in reality one where the time step needed to accurately resolve the solution (this is the actual definition of “want”) is a lot larger than the time scale of how fast perturbations from the solution _decay_ (if the perturbations don’t decay, they’re part of a nearby solution!)

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Rook Bridson @rookbridson.bsky.social · 09/04/2026

The general stiffness issue is that some time integrators are only conditionally stable, with a time step restriction that is smaller than the time steps you want to take — except the “want” here is a loaded term. It’s *not* just the user’s preference, eg. to fit some computational budget.

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Rook Bridson @rookbridson.bsky.social · 09/04/2026

One of the basics of numerical analysis which took me far too long to internalize, and for which there is still a lot of misunderstanding out there in graphics, is the notion of stiffness in time integration, and associated ideas of time step selection, stability, and modeling.

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Rook Bridson @rookbridson.bsky.social · 31/03/2026

…we have far too much bad visibility, bigots projecting their awful fantasies on us to rationalize hatred and violence and legal warfare, setting up trans people as a visible target but replacing our reality with concocted libel

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Rook Bridson @rookbridson.bsky.social · 31/03/2026

On this trans day of visibility, again I am thinking how _good_ visibility is helpful for people who need some kind of role model to be able to figure out that they themselves are trans — it would have helped me realize before my late 40’s!! — but…

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Quanta Magazine @quantamagazine.org · 30/03/2026

David Dunning studied both English and math as an undergraduate. “They felt related to me,” he said. “They were both about the worlds and structures that can be summoned by writing.”

quantamagazine.org

How Writing Changes Mathematical Thought | Quanta Magazine

David E. Dunning explores how mathematical notation is a social, world-building technology.

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Rook Bridson @rookbridson.bsky.social · 31/03/2026

i have anxiety over turning 50 later this year only for the question of how to celebrate it (i do have a dream, which would be perfectly feasible if it weren’t for my pesky personality disorder ruining everything as usual)

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Rook Bridson @rookbridson.bsky.social · 02/03/2026

…so my next step as a pragmatic applied mathematician is generating data from a lot of numerical solutions to try and guess the Taylor coefficient (as a function of problem parameters) or at least something close enough with the right asymptotic behaviour. It’s honestly delightful 😊

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Rook Bridson @rookbridson.bsky.social · 02/03/2026

The context is solving an ODE which is itself an approximation to what I actually want to work on, which alas is an unsolvable nonlinear BVP. My asymptotic analysis took me pretty far but not quite all the way to an accurate approximation near the boundary I care most about,

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Rook Bridson @rookbridson.bsky.social · 02/03/2026

Currently playing "guess the function" (given lots of numerically determined approximate data points)

A plot of a curve f(x) where x goes from 0 to a little over 30, and f(x) drops from 0 to -10 or so, in a slightly convex way.

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Gillian Branstetter @gbbranstetter.bsky.social · 23/02/2026

Disagree with the very concept of the debate but it's less that we care what people think and more that we're punished if we don't. Men are generally rewarded for sociopathy.

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Rook Bridson @rookbridson.bsky.social · 24/02/2026

Oh dear. Now that I think about, it's the same for me with fireworks and garbage trucks...

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Rook Bridson @rookbridson.bsky.social · 24/02/2026

Sigh. A reminder that just because a trans woman is online and even posts the occasional (sfw) selfie it does not mean she is a sexual object; porn-focussed accounts who engage will be blocked.

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Rook Bridson @rookbridson.bsky.social · 14/02/2026

But I do my best to avoid people and places where I might not be safe, and then remind myself nobody else really cares how I present, and the good people already have made it clear I’m accepted and welcomed. That helps get me through the dysphoric days

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Rook Bridson @rookbridson.bsky.social · 14/02/2026

Aw thank you — but I cannot stress enough how much I curate my selfies, throwing out 5+ for each one I keep, and some days I simply cannot find a single one that I like no matter how I pose and mess with lighting etc. I still have days I lack confidence in public, cringe at my reflection, cry…

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Rook Bridson @rookbridson.bsky.social · 14/02/2026

I have been growing out what hair I do have for 1.5 years now, and that lets me go with just a 9”x9” topper instead of a full wig, and it is working really well for me (looks good, convenient, and mostly secure enough just with clips). I think I’m mostly at peace with this now but it’s been rough.

Selfie in a green fleece with loose hair: dark brown from a topper, slightly more auburn from my scalp, but mixed together and difficult to tell apart.

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Rook Bridson @rookbridson.bsky.social · 13/02/2026

I tried minoxidil foam a decent length of time (washing hands really carefully thinking about our dog) but did not find it did all that much, and eventually gave up on it 😕

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Rook Bridson @rookbridson.bsky.social · 12/02/2026

Horrifying thread. Just do not travel to the US.

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Rook Bridson @rookbridson.bsky.social · 11/02/2026

…usually because in a graphics paper the demos look great! But sure enough, every time I actually try it out, I see my understanding was correct, and it’s easy to find a problem where the actual convergence is extremely slow… but didn’t get tested in the paper.

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Rook Bridson @rookbridson.bsky.social · 11/02/2026

Every time I read a paper that claims there method of solving implicit dynamics converges super quickly, but I know it reduces to a very standard stationary iteration for linear problems (and is known to initially make good progress before slowing drastically), I have a bit of self-doubt…

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Rook Bridson @rookbridson.bsky.social · 09/02/2026

Horrifying. And yeah, that makes an absolute no to the idea of US travel for me until It Happens.

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Rook Bridson @rookbridson.bsky.social · 03/02/2026

Anyways, I’m now in the “fun” part of debugging a prototype code which clearly isn’t converging but doesn’t have any obvious disasters; I’m hoping it’s only a typo in the code or at worst an algebra mistake, and there’s nothing deeper that needs thought 😬

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Rook Bridson @rookbridson.bsky.social · 03/02/2026

…prototype reference code that has an attractive structure to follow as well as the nastiest math bits worked out readably, even if it isn’t directly usable in production, and if it’s a big project then also a plan of attack and division of labour for the actual developers to follow.

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Rook Bridson @rookbridson.bsky.social · 03/02/2026

I am absolutely not a software developer, but working with developers I think I am finding my preferred approach to big new algorithmic features — thinking of my output as including an accurate whitepaper with full details of implementing the new algorithm (NOT a conference paper), …

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Rook Bridson @rookbridson.bsky.social · 31/01/2026

When the bug is actually just in your test harness, not the code you're testing...

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Rook Bridson @rookbridson.bsky.social · 31/01/2026

And yet — I can't help but wish that somehow I could also be a dancer, violist, composer, painter, poet, etc. etc. at the level which would be in reach if just one passion, on its own, were the main focus in my life 😂

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Rook Bridson @rookbridson.bsky.social · 31/01/2026

...so I am grateful from the bottom of my heart that I did find a niche in computational mathematics where I can truly feel good at what I do, that demands that mix of depth and breadth to bridge research math with creative industry.

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Rook Bridson @rookbridson.bsky.social · 31/01/2026

My roving curiosity and flexibility are absolutely things I love about myself, but from time to time I'm keenly aware of how I have Too Many Interests to possibly have the time and energy to develop them all. I could so easily be the proverbial jack of all trades, master of none ...

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