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Henrik A. Friberg

@hafriberg.bsky.social
111 followers 99 following 39 posts

Mathematical optimization enthusiast and part of the R&D team at MOSEK ApS.

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Henrik A. Friberg @hafriberg.bsky.social · 20/06/2026
”Kendgerninger er som legeklodser. Med tankens kraft kan vi klikke dem sammen uden samlevejledning, og et større udvalg er både sjovere at lege med og fører oftere til noget interessant.” Fra min egen #lommepoesi
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Henrik A. Friberg @hafriberg.bsky.social · 21/04/2026
Booked my stay at Edinburgh for OP26. Will be arriving on Saturday (30th of May) for ample time to hike in the beautiful landscape. Maybe Ben Nevis, maybe something closer and slightly less challenging. As I travel alone, feel free to text me if you wanna join.
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Reposted by Henrik A. Friberg
Sebastian Pokutta @spokutta.bsky.social · 13/04/2026
For a decade it was open whether Frank-Wolfe's O(1/√ε) rate on strongly convex sets is tight. We show it is: Ω(1/√ε), even for a simple quadratic on a unit ball.
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Henrik A. Friberg @hafriberg.bsky.social · 04/03/2026
So much good stuff here, but I would like to highlight the benefit of practicing. When you know the presentation by heart, you don’t need to spend cognitive effort remembering what to say. That frees attention for connecting to the audience. You'll learn what works and not, they'll stay engaged.
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Henrik A. Friberg @hafriberg.bsky.social · 01/12/2025
The frame freeze and overlay gives a really cool effect, but not a fan of handwriting in digital media.
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Henrik A. Friberg @hafriberg.bsky.social · 07/11/2025
While I haven't finished processing the linked paper, I believe the idea is to limit the set of inputs and give room for error in the output. This is what brings polynomial complexity. The impressive part is when this is achievable by very mild assumptions (satisfied in practice).
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Henrik A. Friberg @hafriberg.bsky.social · 07/11/2025
www2.mathematik.tu-darmstadt.de/~disser/pdfs...
www2.mathematik.tu-darmstadt.de
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Henrik A. Friberg @hafriberg.bsky.social · 07/11/2025
I seem to recall the solution of a knapsack problem being embedded in how many times some columns entered the basis for some specific simplex method, so maybe the bridge for such a result has already been established @sophie.huiberts.me ?
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Henrik A. Friberg @hafriberg.bsky.social · 07/11/2025
I wonder whether something similar can be done in the field of NP-hard problems, to obtain polynomial complexity results by similar (algorithmically mild) assumptions on scaling, perturbations, etc. This would shed light on why we are able to solve knapsack and TSP problems to very high dimension.
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Henrik A. Friberg @hafriberg.bsky.social · 17/09/2025
Great article, and I do like that you address my initial thoughts immediately: "One canonical approach...". Is it common to only have an exam period of 6 days though? That 7 day schedule looks at lot more attractive.
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Henrik A. Friberg @hafriberg.bsky.social · 29/08/2025
That is a much harder question I think. Reminds me of the largest sofa that you can move around a corner problem.
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Henrik A. Friberg @hafriberg.bsky.social · 12/08/2025
Don't forget to ignore posts with foul language. That really removes a lot of junk.
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Henrik A. Friberg @hafriberg.bsky.social · 08/08/2025
If yes, I would try adding a supernode (connected to all) and require flow conservation, an inflow of at least one for the closed neighborhood (setminus supernode) of each node, and minimize the number of used edges. For n=8, this is still a rather small problem for MIP solvers.
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Henrik A. Friberg @hafriberg.bsky.social · 08/08/2025
Is this just one more than the shortest snake needed to visit the closed neighborhood of each node at least once? 🤔
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Henrik A. Friberg @hafriberg.bsky.social · 05/08/2025
Oh, that’s so satisfying! I stopped at the 4-norm ball thinking I had the solution as it fits the hole like a pot lid (has a perfect circle as an intersection).
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Henrik A. Friberg @hafriberg.bsky.social · 05/08/2025
Consider contributing to epoch.ai/frontiermath. As no sizes are given, it is kinda implicitly assumed that "every p norm ball" also includes every size. And with this, you probably want to rule out infinite packings with gap approaching zero, let alone trivial covers of the hole.
epoch.ai
FrontierMath
FrontierMath is a benchmark of hundreds of unpublished and extremely challenging math problems to help us to understand the limits of artificial intelligence.
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Henrik A. Friberg @hafriberg.bsky.social · 24/06/2025
Unfortunately, it seems there is quite a theoretical gap between circles and hula hoops: link.springer.com/article/10.1...
link.springer.com
On Packing $$\mathbb {R}^3$$ R 3 with Thin Tori - Discrete & Computational Geometry
We show that $$\mathbb {R}^3$$ R 3 can be packed at a density of $$0.222\ldots $$ 0.222 … with tori whose minor radius goes to zero. Furthermore, we show that the same torus arrangement yields an asym...
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Henrik A. Friberg @hafriberg.bsky.social · 24/06/2025
So I should be able to fill space with hula hoops without bending them out of shape -- thinner the hoops, better the cover? Sounds impressive.
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Henrik A. Friberg @hafriberg.bsky.social · 19/06/2025
I have only tried for small code snippets and can't say its making me more productive, but it's definitely interesting and stimulates another skill set.
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Henrik A. Friberg @hafriberg.bsky.social · 19/06/2025
Having a strong background in programming, I find that code generation is a great exercise for peer reviewing. It starts with the naive approach, and then you iteratively refine it by corner case handling, performance tuning and simplification. Not unlike how some educational books are written.
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Henrik A. Friberg @hafriberg.bsky.social · 16/06/2025
It seems to me they distribute from their strongest military positions to minimize operational risk, using small boxes (=frequent revisits) to get better tracking of where it goes.
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Henrik A. Friberg @hafriberg.bsky.social · 11/06/2025
Has anyone built enough intuition for Gomory Cuts to dare explain when they are excellent and when they are terrible in this game?
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Henrik A. Friberg @hafriberg.bsky.social · 06/06/2025
The quote “I would have written a shorter letter, but I did not have the time” comes to mind.
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Henrik A. Friberg @hafriberg.bsky.social · 26/05/2025
Nice goal. I may object that the floors and ceils are a bit hard to distinguish, or is it just me? ⌊|⌈⌉|⌋|⌊
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Henrik A. Friberg @hafriberg.bsky.social · 21/05/2025
I haven’t tried it yet, but the new kid on the block is Typst with Hayagriva for citations. Categories seems to make sense: github.com/typst/hayagr...
github.com
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Henrik A. Friberg @hafriberg.bsky.social · 26/04/2025
I like this. A 68% confidence interval around 10 is probably quite a good model for what people actually mean when they say 10 ± 1 and do the hand gesture.
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Henrik A. Friberg @hafriberg.bsky.social · 25/04/2025
10 ± 1 is (a) the boolean expression "9 or 11", (b) the set {9, 11}, (c) the interval [9, 11], (d) an ambiguous operation that can't be used without context?
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Henrik A. Friberg @hafriberg.bsky.social · 10/04/2025
Consider the LP problem min{cᵀx : Ax=b, x≥0} with dual max{bᵀy : Aᵀy≤c}. Adding Gaussian noise with std σ to all of A and c, the problem can be solved by a dual simplex method in O( 1/sqrt(σ) n^2.75 log(m)^1.75 ) pivot steps following the shadow vertex pivot rule. See arxiv.org/abs/2504.041....
arxiv.org
Optimal Smoothed Analysis of the Simplex Method
Smoothed analysis is a method for analyzing the performance of algorithms, used especially for those algorithms whose running time in practice is significantly better than what can be proven through w...
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Henrik A. Friberg @hafriberg.bsky.social · 20/03/2025
Agreed, but it sparks an interesting question. What is the most difficult optimization problem which is simple to explain without math?
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Reposted by Henrik A. Friberg
Sophie Huiberts @sophie.huiberts.me · 12/03/2025
In November 1979, the NYT (🤮) writes of the then-new ellipsoid method that "the discovery may be applicable in weather prediction" Does anyone know how LP would be used in weather prediction?
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Henrik A. Friberg @hafriberg.bsky.social · 21/02/2025
When you are so deep into OR you start thinking about injective functions as 'codomain packing'.. 😅 Let f: X → Y and consider the sets {f(x)} for each element x∈X. The function is injective/surjective/bijective if and only if these sets forms a packing/covering/partitioning of Y.
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Henrik A. Friberg @hafriberg.bsky.social · 14/02/2025
In Denmark it’s called “100 meter skoven” (the hundred meter forrest). Sounds tiny in comparison, but I always thought of it as referring to a feature of the forrest rather than its extend.
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Reposted by Henrik A. Friberg
Mosek Team @mosek.com · 07/02/2025
Our latest blogpost is a little weekend treat for everybody interested in conic reformulations! themosekblog.blogspot.com/2025/02/a-sm...
themosekblog.blogspot.com
A small breakthrough in the modeling of polynomial denominators
The MOSEK ApS official blog: announcements, new releases, activities, optimization modeling hints and examples.
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Henrik A. Friberg @hafriberg.bsky.social · 27/01/2025
Today's word: Neutrosophic Number. Used to represent performance indicators such as product quality, delivery time, and cost, in the form of survey answers. An example is a triple such as (satisfied, uncertain, unsatisfied) = (70%, 10%, 20%).
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Henrik A. Friberg @hafriberg.bsky.social · 23/01/2025
Can you explain what the graph is showing or perhaps share a link to find the slides?
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Henrik A. Friberg @hafriberg.bsky.social · 30/12/2024
If so, we suddenly have an observer paradox like the one which inspired Einstein to his theory of relativity. Does either observer see quantum mechanical properties in the other, without experiencing it themselves?
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Henrik A. Friberg @hafriberg.bsky.social · 30/12/2024
The double-slit experiment has been replicated with big molecules so quantum phenomena definitely generalizes from particles to larger subsystems. But does it generalize to space rockets far out in the cold and empty universe?
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Henrik A. Friberg @hafriberg.bsky.social · 30/12/2024
In physics, if you isolate a subsystem from interaction it allows for quantum mechanical behavior in that subsystem. But is that only from our perspective?
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Henrik A. Friberg @hafriberg.bsky.social · 11/12/2024
This talk adds a whole new level of depth to the diet problem, showing that operations research is not always the science of better. Worth watching!
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Henrik A. Friberg @hafriberg.bsky.social · 29/11/2024
Let's not fight over the squircles name. It can denote the entire family of shapes given by |x|^p + |y|^p = s |x|^p |y|^p + 1 for p≥2 and 0 ≤ s ≤ 1, changing continuously from a circle to a square for both p→∞ and s→1.
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Henrik A. Friberg @hafriberg.bsky.social · 26/11/2024
Why aren't we always solving the convex Lagrange dual problems and extracting primal solutions from the dual variables? I investigated the duality gap at or.stackexchange.com/questions/12....
or.stackexchange.com
If the Lagrangian dual function is always concave, why aren't we "just" solving dual problems optimally?
Let $\mathcal{P}$ be the following primal optimization problem \begin{align} \mathcal{P}: \text{minimize}_x \quad & f_0(x)\\ \text{subject to} \quad & f_i(x) \leq 0, \quad i = 1, ..., m \\ ...
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Henrik A. Friberg @hafriberg.bsky.social · 20/11/2024
Would love to hear more about 'scopping' in operations research - is it an issue? In other fields of research (e.g., biochemistry) it is quite common that big research groups outpace smaller ones, and so, as a small lab with a top notch project, you can't share too openly.
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