Joshua Grochow
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joshuagrochow.bsky.social
Joshua Grochow
@joshuagrochow.bsky.social
2.3K followers 480 following 1.4K posts
Research: TheoryCompSci, pure math, complex systems
Other: climate; covid; equity, inclusion, & accessibility

Assoc. Prof. @ CU Boulder Comp. Sci. & Math
Views my own

@[email protected] (& prev twitter)

https://home.cs.colorado.edu/~jgrochow
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joshuagrochow.bsky.social
Is this...good?
You scored 100% Stop Hate UK Stop Hate. Start Here A joint project
November 5, 2025 at 2:51 AM
joshuagrochow.bsky.social
StackOverflow may be dying (genAI is pretty decent at the basic mechanics of coding), but the Theoretical CS StackExchange (while always a smaller community) is still basically just chugging along:
Chart of new questions per month on the TCS StackExchange, 2016-2025. Wiggly line like a stock price, maxes around 80, min around 30. Slight downward trend but to the naked eye the average looks to be around 45-50, pretty consistently since 2019.
May 30, 2025 at 10:05 PM
joshuagrochow.bsky.social
From the article.

I'll admit I was skeptical just based on the quoted post, but I (think) I like where the article ended up.
Something similar has to happen with academic integrity in a world where LLMs are now ubiquitous. We need to think about academic integrity as a bigger concept rooted in educational values, values that are tied to student engagement, effort and learning. I’m convinced we’re significantly underestimating the degree and kinds of changes that need to happen in educational institutions to deal with the existence of generative AI technology. These changes need to deal not only with the technological capabilities, but also with the deterministic way the technology is being framed by those who are developing and boosting it. Some of this boosting is happening inside of higher education institutions that have decided—without a ton of hard evidence, by the way—that AI is an inevitable part of our collective and individual futures. I have no desire to wall education off from artificial intelligence, but the notion of its inevitability is something I think we should resist with what remains of our might.
December 6, 2024 at 6:13 PM
joshuagrochow.bsky.social
18. @pwnallthethings.bsky.social Any finite subgroup of n x n complex matrices has an Abelian normal subgroup of index bounded by a function of n alone (and by (n+1)! for n \geq 71). Collins (J. reine '08) also has an analogue over arbitrary fields, but the statement is a little more complicated:
Theorem A. Let k be an algebraically closed field of positive characteristic ell and let G be a finite subgroup of GL(n,k). Put G-bar = G/O_ell(G). If n \geq 71, then G-bar has normal subgroups N,L such that (i) N is abelian (ii) L = E_ell(G-bar), and (iii) [G : LN] \leq (n+2)! if ell divides n+2, and (n+1)! otherwise If the bound is achieved, then E(G-bar) is simple and G-bar/Z(G-bar) is isomorphic to S_{n+2} or S_{n+1}, respectively. Furthermore, O_ell(G)=1 unless n is congruent to -1 (mod ell), in which case O_ell(G) may be elementary abelian.
November 9, 2024 at 10:05 PM
joshuagrochow.bsky.social
14. @chantzy.bsky.social Sometimes things look discontinuous because we don't have all the information. For example, in the attached slide the 2D shadows appear to have "corners", but w/ all the information (all 3 parameters) we see only smooth surfaces.

(my slide, I'll have to dig up image credit)
Hidden variables create (the appearance of) complexity. Three sequences of 3D figures and their 2D projections/shadows: - A rotating donut. When it becomes vertical enough, corners appear in its 2D projection - A smooth surface bending a bit creates a football-like shadow - A smooth surface bending in a different way creates an X-like shadow (called a swallowtail) - A smooth surface bending in yet a third way creates the appearance of corners, that expand to two meeting circles, that eventually separate.
November 8, 2024 at 6:35 PM
joshuagrochow.bsky.social
I wanted to share some things I think are amazing and cool. Each like -> one theorem (or definition or phenomenon or example or...). #MathSky
Poorly edited text graphic reading "Get to know my math taste. For every like, I will post one theorem I love ❤️"
November 7, 2024 at 10:18 PM
joshuagrochow.bsky.social
New (*draft) slide just dropped, that I want to include at the start of all my online talks. Thoughts or feedback?

#MathSky #AcademicSky
Slide title: Thank You for Hosting Remote Talks Body of slide: Many researchers cannot travel because of: - Visa issues - Disability - Personal or family health issues - Money - personal, university, country - Family responsibilities - Work responsibilities - (Climate change & environmental cost) [Highlighted] Remote events help tie us to the community!
October 25, 2024 at 3:14 PM
joshuagrochow.bsky.social
It has become unbearable to manually scroll back and forth between the main text and the references at the end of a paper.
#AcademicSky #MathSky #SciSky 🧪
Bernie Sanders meme "I am once again asking you...if you use LaTeX, \usepackage{hyperref}"
September 18, 2024 at 11:35 PM
joshuagrochow.bsky.social
Phoebe teaching Joey French, from Friends meme Phoebe: Step 1 Joey: Step 1 Phoebe: Step 2 Joey: Step 2 Phoebe: Step 3 Joey: Step 3 Phoebe: So the answer is... [looking expectantly] Joey: [looking excited, like he figured it out] So what's the answer?
July 10, 2024 at 4:32 PM
joshuagrochow.bsky.social
Tag yourself.

#Algebra #Math 🧮 #physics
Alignment chart: Lawful Good: non-commutative (hyphenated) Neutral Good: noncommutative (not hyphenated) Chaotic Good: non commutative (with a space) Lawful Neutral: non-Abelian (hyphenated, capital A) True Neutral: nonabelian (not hyphenated, lowercase a) Chaotic Neutral: non Abelian (space, capital A) Lawful Evil: non-abelian (hyphenated, lowercase a) Neutral Evil: non abelian (space, lowercase a) Chaotic Evil: nonAbelian (no space, no hyphen, capital A)
June 28, 2024 at 5:03 AM
joshuagrochow.bsky.social
Best April Fools I've seen so far is the website from the Lab for Atmospheric & Space Physics at CU Boulder: lasp.colorado.edu

It's worth clicking & scrolling, they really went all out!

(h/t Liz Bradley)

🧪
Logo for LASP: Large Animal Space Program Elephant strapped into a hot air balloon floating above the atmosphere of the ball of the Earth
April 1, 2024 at 10:08 PM
joshuagrochow.bsky.social
The 19 April 2024 meeting of Functor Categories for Groups will be hybrid!
www.lancaster.ac.uk/maths/fcg/

To register for the event or to receive the talk links, please email the organiser Nadia Mazza www.lancaster.ac.uk/maths/people...

#MathSky
Groups come in many fascinating forms and shapes. In this meeting, we will survey a selection of original techniques in the study of some infinite groups, such as right-angled Artin and Coxeter groups, profinite groups and groups associated to a certain Cantor action. Techniques may involve graphs, the use of micro-supported actions, or Mackey functor methods. Provisional timetable 13:15-14:15 Jakub Waniek (Lancaster) 14:20-15:20 Dominik Francoeur (Newcastle) 15:20-15:50 refreshments 15:50-16:50 Gemma Crowe (Heriot Watt) Titles & abstracts nearer the time.
February 16, 2024 at 9:45 PM
joshuagrochow.bsky.social
*Hybrid* Summer School on Formal Techniques,  May 25 - June 3, 2024 fm.csl.sri.com/SSFT24 (US Pacific Time)

Applications due April 30th.

I'm particularly excited to see J. Urban's "Combining #MachineLearning and Theorem Proving" and L. de Moura & D. T. Christiansen's "#Lean 4"
The lecturers at the school include: Josef Urban - Combining Machine Learning and Theorem Proving Marsha Chechik - Elicitation and Formal Reasoning about Normative Requirements Leonardo de Moura and David Thrane Christiansen - The Lean 4 programming language and theorem prover Cesare Tinelli - Modeling and analyzing reactive systems with logic-based symbolic model checkers Armando Solar-Lezama - Neurosymbolic Programming for Better Learning
February 15, 2024 at 11:21 PM
joshuagrochow.bsky.social
SIGEcom Winter Meeting this Thursday (15 Feb 2024) online: www.sigecom.org/meetings/win....

Free registration

This year's topic is behavior models with a great lineup of speakers!
All times listed in US Eastern Time Zone (ET). See here for detailed schedule including abstracts. 11:10 - 1:00pm: Introductory Talks (Seminar room) 11:10am - 12:00pm: Jon Kleinberg - Behavioral Agents in Algorithmic Environments 12:00pm - 12:10pm: Break 12:10pm - 1:00pm: Ori Heffetz - EBRD and Market Design 1:00pm - 2:30pm: Social Break 1:15pm - 1:45pm: Student Fireside Chat with Noam Nisan and Al Roth (Lounge) 2:00pm - 2:30pm: SIGecom Advisors Meet and Greet (Gazebo) 2:00pm - 2:30pm: SIGecom Execs Office Hours (Garden) 2:30pm - 5:00pm: Spotlight talks (Seminar room) 2:30pm - 3:00pm: Modibo Camara - Computationally Tractable Choice 3:00pm - 3:30pm: Ryan Oprea - What Makes a Rule Complex 3:30pm - 3:45pm: Break 3:45pm - 4:15pm: Gali Noti - Learning When to Advise Human Decision Makers 4:15pm - 4:45pm: Nicole Immorlica - Data, the Fundamental Particle of Interaction 4:45pm - 5:00pm: Concluding Remarks (Seminar Room) 5:00pm - 6:00pm: Closing Reception (Garden)
February 13, 2024 at 9:36 PM
joshuagrochow.bsky.social
#AcademicSky #MathSky
Bernie Sanders w/ text overlaid: I am once again asking departments To please say what university, department, & position a rec letter is for when requesting letters by email.
October 25, 2023 at 6:10 PM
joshuagrochow.bsky.social
(Some people tried to make "skeet" happen, but thankfully I see that falling by the wayside)
Picture of Rachel McAdams in "Mean Girls", wearing a Santa hat, with white text overlayed: Stop trying to make "skeet" happen
October 11, 2023 at 10:32 PM
joshuagrochow.bsky.social
Convenient covid air decay calculator 👇 based on UV index, temperature, and humidity. Seems esp. useful for places with poor ventilation. Website includes background and caveats of the model.
Screenshot Title: SARS-CoV-2 Airborne Decay Calculator Three white boxes with slider bars, titled "UV Index", "Temperature", "Relative Humidity" UV Index is set at 2, Temperature set at 70F=21.1C, relative humidity cut off in image COVID Stability: white box containing a table with column headers: % Virus Decay, Minutes, [next colun cut off in image] Table rows: 50% (half-life), 9.93 minutes 90%, 37.98 minutes 99%, 65.97 minutes
September 27, 2023 at 5:03 PM