David Bindel
@dbindel.bsky.social
Professing computing and applied math at Cornell. Numerical methods for data science, plasma physics, other stuff depending on the day. Director, Cornell Center for Applied Mathematics; Director, Simons Collaboration on Hidden Symmetries and Fusion Energy.
Reposted by David Bindel
How do you calculate the molecular weight of guacamole?
By using Avocado's Number.
By using Avocado's Number.
November 10, 2025 at 7:38 PM
How do you calculate the molecular weight of guacamole?
By using Avocado's Number.
By using Avocado's Number.
Layers with Kronecker product structure would be equivalent to this, and I believe that has been used.
Silly question: are there 'standard' neural networks based on matrix-matrix multiplies? i.e. instead of propagating a vector with matvecs and activations, propagating a matrix with matmats and activations?
November 6, 2025 at 11:48 AM
Layers with Kronecker product structure would be equivalent to this, and I believe that has been used.
Reposted by David Bindel
I see we’re fighting autism wars today. Here’s a fun fact: it does not require a cure
November 4, 2025 at 3:27 PM
I see we’re fighting autism wars today. Here’s a fun fact: it does not require a cure
Pinky and the Brain.
November 4, 2025 at 12:02 PM
Pinky and the Brain.
Most hilarious collection of dad jokes EVER.
sometimes I think math is a whole extremely-long running inside joke that's not actually very funny
October 31, 2025 at 11:20 AM
Most hilarious collection of dad jokes EVER.
Reposted by David Bindel
The Python Software Foundation was recommended for a $1.5M grant from the National Science Foundation. The terms of the award said PSF could not work on DEI, whether or not the grant funding was used for it.
PSF therefore declined the funding.
Science suffers, but commitment to core values remains
PSF therefore declined the funding.
Science suffers, but commitment to core values remains
TLDR; The PSF has made the decision to put our community and our shared diversity, equity, and inclusion values ahead of seeking $1.5M in new revenue. Please read and share. pyfound.blogspot.com/2025/10/NSF-...
🧵
🧵
The official home of the Python Programming Language
www.python.org
October 27, 2025 at 5:31 PM
The Python Software Foundation was recommended for a $1.5M grant from the National Science Foundation. The terms of the award said PSF could not work on DEI, whether or not the grant funding was used for it.
PSF therefore declined the funding.
Science suffers, but commitment to core values remains
PSF therefore declined the funding.
Science suffers, but commitment to core values remains
Reposted by David Bindel
Your regular reminder that NSF is required by US law to support increasing the participation of historically less represented groups in science and technology fields
October 28, 2025 at 1:55 AM
Your regular reminder that NSF is required by US law to support increasing the participation of historically less represented groups in science and technology fields
OK, #MathSky. This reminds me of a reference-chasing exercise that came up again recently, and maybe someone here will know.
First, a perspective: covariance is almost an inner product (it is an inner product on mean 0 rvs). So what @ccanonne.github.io cites is the Pythagorean theorem.
First, a perspective: covariance is almost an inner product (it is an inner product on mean 0 rvs). So what @ccanonne.github.io cites is the Pythagorean theorem.
Here's a classic (but fun to show) fact: if X is any random variable (with a finite variance) and λ is a real, then
𝔼[(X-λ)²] = Var[X]+(𝔼[X]-λ)²
(In particular, this shows that 𝔼[X] is the quantity minimizing 𝔼[(X-λ)²] over all λ, and that Var[X] is the resulting value.)
𝔼[(X-λ)²] = Var[X]+(𝔼[X]-λ)²
(In particular, this shows that 𝔼[X] is the quantity minimizing 𝔼[(X-λ)²] over all λ, and that Var[X] is the resulting value.)
![A short proof: here is the LaTeX code.
**Proof.** We have, for any $\color{blue}{\lambda} \in\mathbb{R}$,
\begin{align*}
\mathbb{E}[(X-\color{blue}{\lambda})^2]
&= \mathbb{E}[(X-\color{red}{\mathbb{E}[X]} + \color{red}{\mathbb{E}[X]} - \color{blue} {\lambda})^2] \\
&=\mathbb{E}[(X-\color{red}{\mathbb{E}[X]})^2 + 2(X-\color{red}{\mathbb{E}[X]})(\color{red}{\mathbb{E}[X]} - \color{blue} {\lambda}) + (\color{red}{\mathbb{E}[X]} - \color{blue} {\lambda})^2]\\
&=\underbrace{\mathbb{E}[(X-\color{red}{\mathbb{E}[X]})^2]}_{=\textrm{Var}[X]} + 2\underbrace{\mathbb{E}[X-\color{red}{\mathbb{E}[X]}]}_{=0}(\color{red}{\mathbb{E}[X]} - \color{blue} {\lambda})] + (\color{red}{\mathbb{E}[X]} - \color{blue} {\lambda})^2
\end{align*}
and that's all. (The first step is a trick known as *"hiding zero:"* writing $0=a-a$. 🤷)](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:ac6qioenkpl3jmmnib3tpbhb/bafkreieevv3petzx4kqxx3o6i4oqtugsjh52n7i2ellidxmetefboag6fi@jpeg)
October 13, 2025 at 6:12 PM
OK, #MathSky. This reminds me of a reference-chasing exercise that came up again recently, and maybe someone here will know.
First, a perspective: covariance is almost an inner product (it is an inner product on mean 0 rvs). So what @ccanonne.github.io cites is the Pythagorean theorem.
First, a perspective: covariance is almost an inner product (it is an inner product on mean 0 rvs). So what @ccanonne.github.io cites is the Pythagorean theorem.
Things are all pear-shapes, and yet, I got some bunny paper clips along with my order of whiteboard marker refills, and that sparks joy.
October 7, 2025 at 1:50 AM
Things are all pear-shapes, and yet, I got some bunny paper clips along with my order of whiteboard marker refills, and that sparks joy.
Reposted by David Bindel
"There are lots of problems in mathematics that are interesting but have not been solved, and every time you solve one you think up a new one. Mathematics, therefore, is something that expands rather than contracts." – Mary Ellen Rudin (1924– 2013)
#quote #mathematics #problems #maths #math
#quote #mathematics #problems #maths #math
October 3, 2025 at 4:07 PM
"There are lots of problems in mathematics that are interesting but have not been solved, and every time you solve one you think up a new one. Mathematics, therefore, is something that expands rather than contracts." – Mary Ellen Rudin (1924– 2013)
#quote #mathematics #problems #maths #math
#quote #mathematics #problems #maths #math
On the AC Transit to Berkeley for day 3 of Developments in Modern Methods for Linear Algebra... aka DMML, aka happy 70th to my PhD advisor, Jim Demmel.
Realized that I am now the same age he was about halfway through my PhD years...
Realized that I am now the same age he was about halfway through my PhD years...
October 4, 2025 at 1:56 PM
On the AC Transit to Berkeley for day 3 of Developments in Modern Methods for Linear Algebra... aka DMML, aka happy 70th to my PhD advisor, Jim Demmel.
Realized that I am now the same age he was about halfway through my PhD years...
Realized that I am now the same age he was about halfway through my PhD years...
Reposted by David Bindel
gender norms admit the existence of gender metrics which can be abstracted to gender topologies which, here, we categorify into gender locales, also known as pointless genders
October 2, 2025 at 5:23 PM
gender norms admit the existence of gender metrics which can be abstracted to gender topologies which, here, we categorify into gender locales, also known as pointless genders
In a day of wtf nat'l news moments (again!), I also know:
- Today was AppleFest in Ithaca! And yesterday, and tomorrow.
- K1 is out enjoying a concert, and has been noodling around on his guitar all week.
- K2 just got back from playing basketball and is heading to a sleepover soon.
- Today was AppleFest in Ithaca! And yesterday, and tomorrow.
- K1 is out enjoying a concert, and has been noodling around on his guitar all week.
- K2 just got back from playing basketball and is heading to a sleepover soon.
September 28, 2025 at 12:04 AM
In a day of wtf nat'l news moments (again!), I also know:
- Today was AppleFest in Ithaca! And yesterday, and tomorrow.
- K1 is out enjoying a concert, and has been noodling around on his guitar all week.
- K2 just got back from playing basketball and is heading to a sleepover soon.
- Today was AppleFest in Ithaca! And yesterday, and tomorrow.
- K1 is out enjoying a concert, and has been noodling around on his guitar all week.
- K2 just got back from playing basketball and is heading to a sleepover soon.
Reposted by David Bindel
Your daily opossum break:
June 15, 2025 at 10:49 PM
Your daily opossum break:
Reposted by David Bindel
I have taken
the Tylenol
that was in
the medicine cabinet
and which
they think probably
is the reason
you like trains
forgive me
but that’s bullshit
you got autism
from your dad
the Tylenol
that was in
the medicine cabinet
and which
they think probably
is the reason
you like trains
forgive me
but that’s bullshit
you got autism
from your dad
September 23, 2025 at 12:02 AM
I have taken
the Tylenol
that was in
the medicine cabinet
and which
they think probably
is the reason
you like trains
forgive me
but that’s bullshit
you got autism
from your dad
the Tylenol
that was in
the medicine cabinet
and which
they think probably
is the reason
you like trains
forgive me
but that’s bullshit
you got autism
from your dad
Reposted by David Bindel
🚀 NY-CURES Launch — Championing State-Wide Investment in Science! 🚀
Our new coalition advocates for sustained public support of New York’s vibrant biomedical research ecosystem — creating cures, economic gains & strengthening communities.
Sign up. Stay informed. Join the movement: www.nycures.org/
Our new coalition advocates for sustained public support of New York’s vibrant biomedical research ecosystem — creating cures, economic gains & strengthening communities.
Sign up. Stay informed. Join the movement: www.nycures.org/
September 4, 2025 at 4:32 PM
🚀 NY-CURES Launch — Championing State-Wide Investment in Science! 🚀
Our new coalition advocates for sustained public support of New York’s vibrant biomedical research ecosystem — creating cures, economic gains & strengthening communities.
Sign up. Stay informed. Join the movement: www.nycures.org/
Our new coalition advocates for sustained public support of New York’s vibrant biomedical research ecosystem — creating cures, economic gains & strengthening communities.
Sign up. Stay informed. Join the movement: www.nycures.org/
Reposted by David Bindel
It should be needless to say, but it is perhaps at this moment worth saying, that transgender individuals have the same right as anyone else to life, liberty, and the pursuit of happiness.
September 14, 2025 at 2:32 PM
It should be needless to say, but it is perhaps at this moment worth saying, that transgender individuals have the same right as anyone else to life, liberty, and the pursuit of happiness.
Reposted by David Bindel
This fucking sucks. Our Chinese colleagues are valued colleagues. I am so tired of the bipartisan yellow threat shit. www.cnn.com/2025/09/11/s...
Trump admin escalates space race with China, banning visa-holding scientists from working at NASA | CNN
NASA has banned Chinese citizens with US visas from participating in agency programs — a dramatic escalation in the space race between China and the United States.
www.cnn.com
September 12, 2025 at 2:48 AM
This fucking sucks. Our Chinese colleagues are valued colleagues. I am so tired of the bipartisan yellow threat shit. www.cnn.com/2025/09/11/s...
Reposted by David Bindel
The great Zen teacher Thich Nhat Hanh's poetic antidote to anger www.themarginalian.org/2022/02/01/f...
August 28, 2025 at 1:28 PM
The great Zen teacher Thich Nhat Hanh's poetic antidote to anger www.themarginalian.org/2022/02/01/f...
There does exist techno-babble-sounding jargon in the world. But then there's technical jargon as captured from a research conversation today: "I'm tracing long enough to capture many bananas." Plain, short, descriptive... and yet, it takes some experience to have any clue what's being said.
August 27, 2025 at 8:16 PM
There does exist techno-babble-sounding jargon in the world. But then there's technical jargon as captured from a research conversation today: "I'm tracing long enough to capture many bananas." Plain, short, descriptive... and yet, it takes some experience to have any clue what's being said.
Reposted by David Bindel
(long, reluctant sigh)
sub-terfuge
sub-terfuge
Attorney General Pam Bondi says that the "Subway Slinger" who chucked a sandwich at a federal agent in DC the other night is actually a DOJ employee. She describes him as an "example of the deep state."
August 14, 2025 at 6:03 PM
(long, reluctant sigh)
sub-terfuge
sub-terfuge
The movers will come tomorrow to take my stuff to my office in the new building. I will still spend some time in this office (I am CAM director through end of June 2028). But the books are moving.
August 14, 2025 at 8:33 PM
The movers will come tomorrow to take my stuff to my office in the new building. I will still spend some time in this office (I am CAM director through end of June 2028). But the books are moving.
Reposted by David Bindel
Discworld QOTD, from Night Watch
“Once you get troops on the streets, it’s only a matter of time before it goes bad. Some kid throws a stone, next minute there’s houses on fire and people getting killed.”
“Once you get troops on the streets, it’s only a matter of time before it goes bad. Some kid throws a stone, next minute there’s houses on fire and people getting killed.”
Discworld QOTD, from Eric
“The captain glared at him. The sergeant put on the poker face that has been handed down from NCO to NCO ever since one protoamphibian told another, lower-ranking protoamphibian to muster a squad of newts and Take That Beach.”
“The captain glared at him. The sergeant put on the poker face that has been handed down from NCO to NCO ever since one protoamphibian told another, lower-ranking protoamphibian to muster a squad of newts and Take That Beach.”
Discworld QOTD, from The Last Hero
“Too many people, when listing all the perils to be found in the search for lost treasure or ancient wisdom, had forgotten to put at the top of the list "the man who arrived just before you".”
“Too many people, when listing all the perils to be found in the search for lost treasure or ancient wisdom, had forgotten to put at the top of the list "the man who arrived just before you".”
August 12, 2025 at 6:21 PM
Discworld QOTD, from Night Watch
“Once you get troops on the streets, it’s only a matter of time before it goes bad. Some kid throws a stone, next minute there’s houses on fire and people getting killed.”
“Once you get troops on the streets, it’s only a matter of time before it goes bad. Some kid throws a stone, next minute there’s houses on fire and people getting killed.”
Reposted by David Bindel
Each Friday, I summarize what happened this week in science 🧪& higher ed. This was Week 29:
- new executive order makes a mockery of peer review
- UCLA facing demand for $1 Billion, patents are latest attack on Harvard
- mRNA, climate assessments & so much more at buttondown.com/liminalcreat...
- new executive order makes a mockery of peer review
- UCLA facing demand for $1 Billion, patents are latest attack on Harvard
- mRNA, climate assessments & so much more at buttondown.com/liminalcreat...
Week 29
Within, amongst, against
buttondown.com
August 9, 2025 at 2:27 PM
Each Friday, I summarize what happened this week in science 🧪& higher ed. This was Week 29:
- new executive order makes a mockery of peer review
- UCLA facing demand for $1 Billion, patents are latest attack on Harvard
- mRNA, climate assessments & so much more at buttondown.com/liminalcreat...
- new executive order makes a mockery of peer review
- UCLA facing demand for $1 Billion, patents are latest attack on Harvard
- mRNA, climate assessments & so much more at buttondown.com/liminalcreat...
Reposted by David Bindel
