@dpiponi@mathstodon.xyz
@dpiponi@mathstodon.xyz avatar

dpiponi

@dpiponi@mathstodon.xyz

Disclaimer:
👽 My opinions are not my own. They're beamed to me by aliens

Current life:
🎮 Epic Games

Previous lives:
🍩 a PhD in Riemann theta functions
💥 many years working in movie visual effects
🎈 some years devising navigation strategies for balloons
🎲 a year drawing random samples from tricky distributions

Likes:
🚴 I like to bike
🏃 I like to run
🎛️ my musical tastes lie towards the electronic end of the spectrum
🚀 I like Andor and The Mandalorian

This profile is from a federated server and may be incomplete. Browse more on the original instance.

dpiponi, to random
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I love the waves of leg motion on this critter that was walking across our driveway.

Very dark red segmented worm like creature with maybe 100 legs that move in waves starting at the back and moving forward.

dpiponi,
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@BartoszMilewski Neural networks are robust like that! I noticed that when it feels threatened it rolls up its head, possibly to protect the antennae.

dpiponi, to random
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I hate typing practice. Seriously. I've been programming computers since before most of you were born. But I need to move on from being a two fingered typist, even if a fast one,

dpiponi,
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@pervognsen You calling it "hell" is very helpful actually! Good to know that the frustration isn't just something I'm doing wrong.

dpiponi, to random
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I have to admit I enjoy seeing familiar sci-fi plots appearing as papers. This one proposes that AIs cause civilizational collapse, explaining the Fermi "paradox".

https://arxiv.org/abs/2405.00042

"AI could represent a major threat to the future course of not only our technical civilisation but all technical civilisations"

dpiponi, to random
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Let me tell you about my embarrassingly stupid C++ mistake so you don't have to make it:

If X is of type std::optional<T> and Y is of type T you can assign Y to X like so:

X = Y

I sort of don't like that because X and Y are different types.

You can also write

*X = Y

which works because *X is of type T&. Now the types match.

But woe is me! Don't do the latter. If X is an empty optional then *X = Y fails silently.

It's obvious when you think about it for a moment. But when you're thinking about the bigger picture you can forget about the little things.

dpiponi, to random
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I kept saying to myself "he's gotta be an alien", "surely he's not human", but in my heart of hearts I didn't really believe it...until...well I'm not giving you any spoilers...

dpiponi,
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@BartoszMilewski The evidence piled up but my priors were low

dpiponi,
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@BartoszMilewski Which is also the theme in The Creator.

dpiponi, to random
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https://www.bbc.com/news/articles/c0kl4glp547o

I blame all the stupid rule based systems for getting your attention. iOS Focus is the most needlessly complex solution to a problem relative to the problem difficulty I've ever seen.

dpiponi,
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@mangoiv Even if you could get your head around it, do you really feel like learning yet another rule based system in order to tell your phone you feel like chilling out for a bit?

JimPropp, to random

Is there a video that provides intuition about why countable subsets of R (even dense ones) have outer measure zero, by zooming in on a cover of such a set by a union of countably many intervals?

dpiponi,
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@johncarlosbaez @JimPropp I've mentioned here before that I find this the most counterintuitive thing I know in mathematics - even though it's sort of obvious.

monsoon0, to random
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Do you want to know more about the mathematics of computing? This @SMBCComics is a great start 👇🏼 https://www.smbc-comics.com/comic/the-talk-3

dpiponi,
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@monsoon0 "quantum computing isn't just a matter of trying all the answers in parallel" That makes a nice change! I hate every other pop-sci description.

dpiponi, to random
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I don't know if I hallucinated this but maybe someone recognises it:

I'm sure I once (~20 years ago) saw an arbitrary precision real number library for C or C++ that worked by picking some fixed precision and worked until it produced a result at the required precision, or, if it convinced itself it couldn't achieve that precision, did some kind of backtracking so it could redo the computation at a higher fixed precision. Somewhat analogously to how transactional memory works - and I think under the hood there may have been some unusual memory model.

Sound familiar to anyone?

dpiponi,
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Maybe it's this https://en.wikipedia.org/wiki/Real_RAM and maybe my own memory is unreliable.

dpiponi,
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Or specifically, I'm now sure it was this implementation: https://irram.uni-trier.de/

That transactional thing might be my own hallucination in which case I like it and maybe I'll implement it...

dpiponi,
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@BartoszMilewski Right. This is a design pattern I've seen a few times, though in Haskell rather than C++.

dpiponi, to random
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I'd love something like algebraic effects in C++. So I could write code like (and this is just a sketch, not a realistic proposal for syntax):

handle (new -> MyOwnMemoryAllocator)
{
int* x = new int[n];
...
}

or

handle(out -> Log)
{
out << "debugging stuff" << endl;
}

dpiponi,
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In the old days we used to routinely install (and chain) our own handlers for effects :)

dpiponi, to random
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Annoying that the Kindle retroactively changes book covers. Such nice art for these books, except book 1 now.

dpiponi, to random
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Big numbers. Who needs them?

https://www.bbc.com/news/articles/c9wz7pvvjypo

dpiponi, to random
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Here's an animation generated by simulating the 2D wave equation kicked off with a Dirac delta pulse. Periodic boundary conditions.

But let's say we want the field value to be as high as possible at a particular point in space at a chosen future moment in time...

video/mp4

dpiponi,
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Let's use gradient descent to optimise the "refractive index" at each point in a square in the middle. After a few iterations we get the following (grey) refractive index leading to the following simulation. Note how it all conspires to arrive at the right point...

video/mp4

dpiponi,
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You could solve this problem using automatic differentiation. It's a lot like training a convolutional neural net because a single time step here is essentially a (spatially varying) convolution and you're optimising the parameters that determine a long sequence of such convolutions...

dpiponi,
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In this example I think (not 100% sure) the optimization has tried to construct elliptical mirrors with the start and end at the foci to focus the "direct" wave and parabolic mirrors at the ends to focus the waves that wrap around the domain...

dpiponi,
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But this is much the same problem seismologists solve - finding the material properties based on what signals arrive where from a source. And seismologists were doing this long before convolutional neural nets were invented. So I thought I'd try something closer to what they do. It's also more insightful than just using AD which is something of a black box.

Anyway, here's the result of solving the same problem but getting the focus to happen much later. There's a sort of fractally refractive index now...

video/mp4

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