Dirk Lorenz

For my lecture "Mathematical methods for data analysis and image processing" I do a tl;dr slide at the end. This is the one for PCA:

For my lecture "Mathematical methods for data analysis and image processing" I do a tl;dr slide at the end. This is the one for the Frobenius inner product and gradients in matrix calculus:

For my lecture "Mathematical methods for data analysis and image processing" I do a tl;dr slide at the end. This is the one for the SVD and the pseudoinverse:

For my lecture "Mathematical methods for data analysis and image processing" I do a tl;dr slide at the end. This is the one for linear regression:

"Problem X has fallen" is a framing I've never connected with. I can relate to the feeling that working on a hard problem is a battle, but I don't see the problem as an enemy to be defeated. I see it as something to understand, and understanding isn't something that gets beaten.

Just created an account on mu - find me here: mu.social/profile/dirq...

All well-posed problems are alike; each ill-posed problem is ill-posed in its own way.

Had a hard time grading seminar reports and presentations recently (you know, AI). Idea for next seminar: Give students papers I did not read (but would like to). They need to explain the paper to me (orally and in writing) and the grade is determined only by how good I understand.

Signs that academia may be for you: * eduroam works on the first try * you get your travel reimbursement without having to email anyone twice * you understand your institution’s course management system

Material decomposition with multispectral computed tomography still feels underresearched mathematically!Here is what Jürgen Jeschke and I came up with to better understand what is going on. arxiv.org/abs/2609.25926

Rebrand optimization as argmaxxing

George Dantzig died in 2005. Does anyone have any color photographs of him?

Indeed! Also interesting that there was no urge to emphasize *human* computation or *human* calculation when it became possible that non-humans do these (or was there?)

The International Centre for Mathematical Sciences (ICMS, Edinburgh) is looking for a new Director. Application deadline is July 15. Please share this information with anyone who might be interested. icms.ac.uk/icms-seeks-n...

Every optimization problem is linear if you lift enough

I noticed that LLMs already affect student presentations a lot, but now at #SIAMOP26 I realize that also here, people use ChatGPT et al. to produce their slides (at least, that's the obvious explanation for all the "Why this matters" boxes I see on slides...)

That's a hell of a venue for a plenary talk here at #SIAMOP26

The exponential function has the remarkable property that it is the unique function f that satisfies the differential equation f'(x) = exp(x) with initial value f(0)=1.

Everybody is dead. Chuck Norris is still alive.

Modern technology makes conference evenings in the hotel much more enjoyable!

Prove that you are human - once and for all I can't get past level 4 🤖😬 neal.fun/not-a-robot/

📢 #ISMP2027 comes to Amsterdam! The 26th International Symposium on Mathematical Programming will be held July 25–30, 2027. Join researchers from around the world to discuss advances, challenges, and opportunities in the theory and practice of mathematical optimization. 🔗 ismp2027.mathopt.nl #MOS

Am I right that a function that is not increasing and also not decreasing is in fact just creasing?

So you tell me that when I call scipy's linprog with bounds=none, it uses a lower bound of zero?! Yeah, that makes a lot of sense #scipy!

I submit the following for the fifth derivative.

5 years ago today, Her Maths Story went live with our 1st story. What started as a small idea has grown into a global, supportive community celebrating #WomenInMaths. We’re deeply grateful to everyone who has shared, read, supported & believed in this journey. Here’s to the stories still to come 💛✨

Universidad Técnica Federico Santa María in Valparaiso has a quite iconic campus tbh

These tiles don't cease to amaze - with hexagonal holes you get a lot of symmetry!

And they mix! 🧮 #mathsky

And another one!

Funny Numbers xkcd.com/3184/

New periodic pattern from aperiodic tiles dropped: 🧮 #mathsky

Does anyone have a links to good writing on what "trivial" means in mathematics? How we might define that type of thing? I get why people don't like the term, I want to help students seek out trivial examples/results as a way of getting familiar with whatever property we're working with. #MathSky

New paper out! Together with my postdoc advisors @esoubies.bsky.social and Cédric Févotte :) We study the optimization landscape of L0-Bregman relaxations, which naturally arise when one optimizes non-quadratic fidelity terms coupled with the L0-norm. 1/n

New on arXiv: Why noise matters in learned regularization! Data-driven regularizers fail without noise structure. 🎯 Tikhonov, Lavrentiev, quadratic — not equal under non-white noise. 🤫 Spoiler: Optimal reconstruction needs proper noise modeling. 👉 Regularizer choice = structure and noise.

What does it mean to do mathematics? Read my personal answer here: web.mathi.uni-heidelberg.de/content/uplo... #mathsky #math #question

So you agree that the sine function is not decreasing, but you won't say that it's non-decreasing? But alas math has such a precise language! 🧮

Ta daaa! I give you the Lorentz Attractor thanks to the free pattern from #ThreadedTheorems and also @samjshah.bsky.social whose posted work I admired. #StemBroidery #MathArt #MathSky

Join us for a panel on “Careers in Mathematics of Data Science” tomorrow morning!

Our latest WebMDS webinar was a blast! Check out our panel discussion of "Careers in Mathematics of Data Science" on youtube: youtu.be/qdlJJLT4ddQ?...

Register at siam.zoom.us/webinar/regi...

Save the Date! The SIAM Activity Group on Data Science (SIAG/DATA) invites you to join us for a panel on the topic: Careers in Mathematics of Data Science Tuesday, August 12, 2025 | 9:00 AM PT | Zoom Webinar Panelists: Marta D’Elia, Elizabeth Newman, David Uminsky

I've invented a simple, lovely math puzzle I expect every AI fails: Suppose you're a mathematical sailor at sea on a boat that has a perfectly cylindrical hole in the floor. All you brought is a collection of every p norm ball except p=2 (drat!). What do you do to cork the hole and save yourself?

A: A mathematical statement/concept makes intuitive sense. B: There is a sound framework where a mathematical statement/concept can be proven/defined. I tend to believe that A ⇒ B, but not vice versa. (Thinking about Dirac's delta and the Banach-Tarski paradox, for example.) #🧮