@narain@mathstodon.xyz avatar

narain

@narain@mathstodon.xyz

Associate professor of computer science at IIT Delhi. Computer graphics, numerical methods, bad jokes.

I was on Mastodon before it was cool. But it's nice to have all you cool people here now too.

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dpiponi, to random
@dpiponi@mathstodon.xyz avatar

Given a random number generator that generates points uniformly in the unit interval [0,1] can you generate uniformly distributed points in the unit circle using only algebraic functions? In a finite number of steps - so no rejection sampling, loops, recursion. No "almost always" finite either.

Just wondering about sitiations where it seems you can't avoid trig functions.

narain,
@narain@mathstodon.xyz avatar

@BoydStephenSmithJr @dpiponi But first you need to generate some samples from a normal distribution! It's probably just as hard to do that algebraically.

gregeganSF, (edited ) to random
@gregeganSF@mathstodon.xyz avatar

Are you OK, Science magazine?

“The therapy, an injectable monoclonal antibody callnative to antimalarials used in areas where malaria is endemic; those drugs have to be taed L9LS, offers a possible alterken for several days each month to be protective.”

https://www.science.org/content/article/news-glance-infrared-telescope-debuts-gm-rice-stumbles-maternal-mortality-drops

Edited to add:

This should almost certainly be:

“The therapy, an injectable monoclonal antibody called L9LS, offers a possible alternative to antimalarials used in areas where malaria is endemic; those drugs have to be taken for several days each month to be protective.”

@narain diagnosed inadvertent drag & drop.

narain,
@narain@mathstodon.xyz avatar

@mjambon @gregeganSF Ohhh now it makes sense.

"The therapy, an injectable monoclonal antibody call|native to antimalarials used in areas where malaria is endemic; those drugs have to be ta(ed L9LS, offers a possible alter)ken for several days each month to be protective."

It's an inadvertent drag-and-drop in the word processor. The parenthesised part got moved from its original place at | to where it shouldn't be.

narain, to random
@narain@mathstodon.xyz avatar

I spent a couple hours today working out a Newton method for finding the closest rotation to a given matrix A, i.e. min ‖R − A‖² over R ∈ SO(3). Then I found out that Kugelstadt et al. already figured it out: https://animation.rwth-aachen.de/publication/0561/

Oh well. Glad to verify that I got the same result, but I like my derivation better; it's much shorter :)

narain,
@narain@mathstodon.xyz avatar

@johncarlosbaez Same thing that happens every time you ask Newton's method to find the minimum of a constant function: the gradient and Hessian are both zero and you can't go any further.

narain, to random
@narain@mathstodon.xyz avatar

Hey @lisyarus, I was going through your blog and saw that in your 2D soft-body physics engine post (https://lisyarus.github.io/blog/posts/soft-body-physics.html) you wrote about a technique you derived:

"I don't know a well-established name for this, and a quick google search failed to reveal anything of releavance, so I will call this method /shape matching/. If you know some resources on this, I would love to know them, since I had to derive all the equations myself :)"

Good news: it's literally called shape matching! https://matthias-research.github.io/pages/publications/MeshlessDeformations_SIG05.pdf

(P.S. I know your post is almost a year old, so I'm sorry if someone else has already told you this)

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