kandel (u/kandel) - Readit News

kandel commented on Derivatives, Gradients, Jacobians and Hessians blog.demofox.org/2025/08/... · Posted by u/ibobev

fouronnes3 · 11 days ago

There's something that's always been deeply confusing to me about comparing the Jacobian and the Hessian because their nature is very different.

The Hessian shouldn't have been called a matrix.

The Jacobian describes all the first order derivatives of a vector valued function (of multiple inputs), while the Hessian is all the second order derivatives of a scalar valued output function (of multiple inputs). Why doesn't the number of dimensions of the array increase by one as the derivation order increases? It does! The object that fully describes second order derivation of a vector valued function of multiple inputs is actually a 3 dimensionnal tensor. One dimension for the original vector valued output, and one for each derivation order. Mathematicians are afraid of tensors of more than 2 dimensions for some reason and want everything to be a matrix.

In other words, given a function R^n -> R^m:

Order 0: Output value: 1d array of shape (m) (a vector)

Order 1: First order derivative: 2d array of shape (m, n) (Jacobian matrix)

Order 2: Second order derivative: 3d array of shape (m, n, n) (array of Hessian matrices)

It all makes sense!

Talking about "Jacobian and Hessian" matrices as if they are both naturally matrices is highly misleading.

kandel · 11 days ago

Well for me the Hessian is the second order derivative in the special case where the co-domain is of dim 1. It's just very easy to work with...

kandel commented on Ethereum has blobs. Where do we go from here? vitalik.eth.limo/general/... · Posted by u/bpierre

ForHackernews · a year ago

I suppose the difference is that in most technical topics the complexity is either inherent (quantum mechanics just is this way) or exists for a good reason (consensus algorithms are complicated but they solve a hard problem).

IMHO this is not true in cryptocurrency, which is more akin to a self-sustaining pyramid scheme where the complexity serves to obscure the reality of the thing and draw in more rubes. All the nonsensical jargon around NFTs was trying to hide the fact that paying money for a URL to a jpeg of a monkey is stupid. As best I can gather, all this new "layer 2" nonsense is to try and hide the fact that blockchain is a slow, crappy database.

kandel · a year ago

I mean, it's a technical piece of code (ETH, that is), and every new piece gets a new name. It's not a more complicated terminology than you'd get for compilers or protocols - TCP wikipedia has "TCP provides reliable, ordered, and error-checked delivery of a stream of octets " which has 6 (or 5, depending how you'd count it), technical terms. They're not very abstract, sure, but it's just TCP, and we think that's completely normal.

A logic class will suddenly try to teach you "eqvuilance relations", "Equivalence class", "Quotient set", "Projection", "Kernel" (Specifically in the Eqvuilance relation meaning), "partition", and that's only the terms I found in wikipedia. The class I help along has one more under this subject, and this is a first semester topic that is taught in a few weeks. All of those are technical, and all of those build on some other technical terms such as relations, functions, sets...

I concede that crypto has a bad naming scheme. It all sounds silly.

kandel commented on Ethereum has blobs. Where do we go from here? vitalik.eth.limo/general/... · Posted by u/bpierre

kjkjadksj · a year ago

Once you set that up as crypto, thats it, thats the price. With the present model ad agencies can play all sorts of games with this price, inflating or deflating it to suit immediate business needs. Its a whole meta that will poof into smoke. So unless the new crypto meta captures the benefits to ad agencies the current “estimate” model of pricing has, it won’t see daylight.

kandel · a year ago

Why? It's easy to do it as a varied cost.

kandel commented on Show HN: I made a cheap alternative to college-level math & physics tutoring · Posted by u/eltonlin

vundercind · a year ago

My description probably painted this type as more assholish than I intended—it’s mostly that they’re willing, even in fairly casual conversation, to really dig into fine points, to play devil’s advocate (maybe without saying that’s what they’re doing), to pursue any little thing that they don’t immediately get or that seems contradictory.

Conversationally, they poke, they prod, they chase. I assume this is from being educated in environments where that was the norm, and my guess that this is a style that starts in certain types of prep school (and is then imparted on the less-elite folks who attend a university with that set) is really just a guess, but there sure does seem to be a lot of correlation between school prestige and that kind of affect, in my experience, whatever the cause.

As mentioned, I have similar tendencies, but the tenacity at and commitment to this way of chatting from several elite-college folks I’ve met has been a bit much even for me—with more exposure I suspect I’d come to like it, but as it is it feels like being squished on a microscope slide, though I don’t exactly think that’s their fault and I don’t think they’re trying to give offense—but I do think the fact that it can put a person a bit off balance is part of why they’ve picked it up, it seems like a habit honed in a certain kind of affably-contentious intellectual environment (again, I’m just guessing at the causes here)

kandel · a year ago

On the other hand, a passive student will let you go through an entire proof only to raise his hand when you finish and ask something that implies he did not understand the proof from the start.

Why didn't you say so? You wasted both of our time... I even turned around a few times and asked if everyone was following!

I know it's hard to understand when you don't understand. But I don't know how to deal with this problem and the senior lecturers don't seem to know how to, either...

t. just started lecturing

kandel commented on Swedish composer becomes Spotify's most-famous musician you've never heard of theguardian.com/uk-news/2... · Posted by u/danols

fsloth · a year ago

" faking 750 artist names"

Why would this be problematic? Artist commonly work under one or more pseudonyms. 750 is quite a lot for sure, but is there material difference between that and just a few?

kandel · a year ago

One could say he is dominating an opportunity reserved for small-time artists by deceit.

kandel commented on How to be a good listener tomblog.rip/the-myth-of-t... · Posted by u/greenie_beans

CipherThrowaway · a year ago

>Does anyone else question this common piece of advice?

Absolutely. One thing I notice is that the people sharing this "advice" - while positioning themselves as amazing listeners - seem to have a disgust reaction to people sharing details about their own lives in a conversation.

Personally, if I have something I would like to speak about and feel heard about, I feel most heard when the other person is able to share some of their own thoughts and experiences. I absolutely do not feel heard when they completely remove themselves and their life from the conversation, and hit me with lifeless "open-ended questions" and "that sounds tough" platitudes that could have come from a blog post.

kandel · a year ago

I commented this earlier as well. Relating brings a lot of energy to a conversation, but it's also trickier. I wish I had a better solution

When I was at Amaravati the head monk constantly brought up stories from his life, sometimes endlessly, and it was always nice to sit next to him since it was so energetic.

Here, I related something, and it brings a new thing to talk about, a few new edges.

kandel commented on How to be a good listener tomblog.rip/the-myth-of-t... · Posted by u/greenie_beans

mvkel · a year ago

That's level 1, making it about yourself :)

kandel · a year ago

How is it? It's a direct help.

kandel commented on How to be a good listener tomblog.rip/the-myth-of-t... · Posted by u/greenie_beans

kelseyfrog · a year ago

That's going to fall under clean language. There are some written examples on the aforementioned Clean Language wikipedia article[1] under the examples section.

The point I take away from it is the following question, "Who's doing the framing here?" If you're supporting the other person in framing things themselves, then it leans toward clean language. If you're interjecting your own framing, then it leans away from clean language. Personally, I struggle the most with trying to avoid labeling something as "good" or "bad" for the other person. They're full human beings with their own ability to decide how they feel about something and the best way, in my experience, to decide how you feel about something is to put it into words and notice the feelings that come up as the words are said.

If someone is interjecting their own takes, it gets in the way of that noticing.

I'm really curious what you think about manipulation when you envision yourself listening this way.

1. https://en.wikipedia.org/wiki/Clean_language#Example

kandel · a year ago

A lot of times I use what I think you term as unclean language to inject some energy into the conversation. Without it I feel like the conversation dies, so I relate with my own story, or pass a half-judgement, do something to fire them up. I don't know, it doesn't feel like the best solution, but it's the one I use, any thoughts?