Mathematics - 2022-05-28 (page 1 of 2)

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1:10 AM

Maybe MSE should make a room for Ted's Multivariable Book since there seems to be a share of folks that are using the text for learning. Indelible mark on the zeigeist of multivariable mathematics

Zip Drive?.....haven't heard of one of those since early 2000's......perhaps copy the image over to an external hard drive with TB's of memory?........we have those now in this decade :)

at least upgrade to a Jaz drive

1:24 AM

Sorry. USB 3.0 drive.

Purchased today.

I found the issue. It’s because of PCs. I didn’t initialize the disk as a Mac disk. Once I went back and did that, everything copied seamlessly.

haha.

subliminal message about how welcome the Cult of Steve are....

1:42 AM

i hope you copied your lesliecoin digital wallet. it will soon be worth billions.

2:15 AM

Steve Kerr, you mean?

2:35 AM

hmmmm... not a bad cult to be a part of actually.....

After hearing about Godel I am not sure if I should pursue math for undergraduate.

Math is boring.

3:20 AM

@robjohn yes, I understood that. Just as for any v, $[v]_\beta= P[v]_{\beta'}$, in the same way one can express each of vectors in $\beta$ as linear combinations of vectors in $\beta'$, which gives $[v]_{\beta'}= Q[v]_\beta$.

So $Q=P^{-1}$.

Where you're now using $\beta$ to stand for the matrix whose columns are the vectors in the set $\beta$. :)

This means that, $PQ[v]_{\beta}=[v]_\beta$ for any v. That is, $PQ=I$.

And vice versa.

Overkill:

For any v, Qv=0 implies that PQv=0, whence Iv=v=0. Therefore, Q is invertible.

So, if Pw=0 for any w , then there exists a u (because Q is invertible) such that w=Qu, whence Pw=Iu=u=0. It follows that w=0.

Hence, P is also invertible.

:-)

@TedShifrin this is what I confused me in Robjohn's comment. We usually consider matrix with entries from field.

You have that.

3:28 AM

But if $\beta$ represents a matrix whose columns are vectors $a_i$'s then we don't know if $a_i\in F^n$

I assume here that V= vector space over field F.

The columns are the coordinate vectors of a fixed basis with respect to the basis $\beta$ and the basis $\beta'$ respectively.

@TedShifrin yes, I agree with that. :)

I usually just express the coordinate vectors of the $\beta'$ basis vectors in terms of the $\beta$ basis and then I'm done.

3:45 AM

Since you are talking about linear algebra I had a question based on the quadratic form ideas I read yesterday from your text. So I see how the signs of the eigenvalues will determine the form of my hessian matrix. I was trying to see how we would use this in practice. Because we still have to solve for critical points and if we have critical points then we can put them into our original function and determine what are max and min values.

So we are still finding our max and min values plus finding eignevalues in matrices of $n \geq 4$ is a pain so why do it? Unless it is just to illustrate the cohesiveness of things and it isn't done in applications.

well that was a mouthful...

hessians played a key role in the revolutionary war, and there were n \geq 4 of them. if that's not enough of an 'application' for you, i dunno what to say.

which one of the revolutions? Fight for independence? war of 1812? Convoy of Freedom of 2022?

Stealing back the House 2024?

@leslietownes Haha

koro: you see the historical ignorance we are dealing with here.

Average IQ of mathematicians is 160.

4:03 AM

what's a mathematician?

No discussion of eigenvalues here. The $LDL^\top$ decomposition is way easier.

sometimes I think about how life would be at a planet which is at a safe distance from a blackhole (that is, a planet orbiting a blackhole instead of a star). I came to know that such planets come in a theoretical class of planets called blanets. I don't know if any blanet has been observed till date.

@TedShifrin Guess I'll find out more about it beyond what was discussed in that chapter in due time

I think the show 'Lost in space' made me think about that.

@Koro the original or the more recent version?

4:15 AM

oh, we're all orbiting a black hole. some of us just don't know it yet

@D.C.theIII the one that came out in 2018. Is there an older version too?

there's an older version

@Koro I didn't even know there was a 2017 version...........there was one from the late 90's - early 2000's, and one form when Ted was a youth ( probably the most entertaining of the three)

no, when ted was in early middle age

when ted was already an aging sage

the original lost in space is actually based on ted's memoirs

@leslietownes :-)

4:20 AM

i'm not saying ted is old, but the first edition of multivariable mathematics was published not in english, but in velociraptor

4:33 AM

@D.C.theIII That is the section you supposedly were reading.

@leslietownes please translate

one potato two potato

@AlessandroCodenotti $\Bbb R/\Bbb Z$ is a circle and $\Bbb R^n/\Bbb Z^n$ is a torus.

$S^1$ and torus are not simply connected so it shares more characteristics.

ted: your book was published for dinosaurs because human languages didn't exist yet

... i didn't say it was funny

one potato two potato

It just pops into my head. I wondered why higher homotopy group acts so weird and thought maybe standard $S^n$ is not a correct generalization of $S^1$.

4:48 AM

@TedShifrin I did read about the decomposition, I'm going to have to read it again though because I was tired when I got to that part. I get the use of the elementary matrices and such.

Abstract Space Crack

5:15 AM

Abstract Spacecraft (C++ / Qt Desktop Application)

@Koro see video, let me know what you think

This is non-trivial code to write, lol

Suppose that company X has billed to company Y an amount of A . Y tries to process the payment in the following format: unit rate times quantity. Unit rate is fixed and can't be changed. But business systems at Y allow quantity to be upto 3 decimal places. It is observed that to match A amount, Y must put a quantity that is 4 decimal places which is not allowed in the system.

So if Y puts 0.abc then the amount falls below A and if Y puts 0.ab(c+1), suppose c <9 then the amount exceeds A.

X says that they want their exact amount and won't accept a penny more than their bill.

What should be done?

@AbstractSpaceCrack the video is not opening. :(

I'll try the video after some time. @AbstractSpaceCrack

@D.C.theIII Make sure you grok the connection with high school completing the square.

Abstract Space Crack

forum.qt.io/topic/136830/…

@Koro take the two extremes and average them

@Koro the video works for me (from YT). Yeah, the internet is dropping out everywhere it seems these days

@TedShifrin how do you like the new UI compared to convoluted old one which you kind of thought was too involved for your taste as a mathematical user.

You use M_{@1} notation which later get removed. @ means auto-index encloded in { }

*enclosed

5:34 AM

@AbstractSpaceCrack still the quantity comes with 4 decimal places.

:(

Abstract Space Crack

It took all day to debug this auto-indexing feature until it's perfectly working for the most part. My PC doesn't like > 80*F

@Koro the company should pay the extra fractions of pennies

Yeah, but X won't accept it (that is, they will think that their bill was not paid.)

:(

@AbstractSpaceCrack I saw the video but unfortunately yet I don't know what this stuff Hom () means so I have no comments on the video.

Abstract Space Crack

@Koro just google diagram chasing proofs

to get an idea

It will specialize in those. So you won't be factoring polynomials with it

It's for a different kind of proof. Might be popular with Topos theorists because they're mostly about arrows

Hopefully users will make learning games with it eventually, where perhaps all possible options to choose from that you'd even consider using would be displayed as buttons overlaying the diagram, then they either reach a proof or dead end.

Got to keep it simple, though starting out. So games are not necessary, so it's just an editor / human proof guider to begin with.

Coming to a University Mathematics department near you!

@Koro, if $A, B$ are sets, and $C = \textbf{Set}$ the category of sets. Then $\text{Hom}_C(A,B)$ is conventionally defined to be the set of all function maps $f: A \to B$. That's all!

For a category of modules, say, then you'd use module-preserving maps or in other words the set of all $R$-linear maps for $R$-modules.

or $R$-module homomorphisms is another word. They then get "hom" out of that, capitalize it and you have $\text{Hom}$ the standard notation

5:54 AM

@Koro Can you ring the company?

@copper.hat yes. X is awaiting Y's decision on the matter. Y's finance department is on holiday so Y doesn't know what to say to X.

Maybe write a cheque?

Yeah, Y should discuss that with their finance department on Monday.

6:11 AM

@Koro Lost in Space

@robjohn seems amazing :).

@Koro I used to watch those avidly when I was a kid. I have no idea how they would seem today; I know that a lot of shows I thought were great as a kid look awful now.

lost in space looks entertaining.

it certainly was

@copper.hat indeed :).

In one of the episodes (of the new Lost in space), they showed a creature (which looked like a sketch) which moved(lived?) in vacuum.

6:24 AM

@Koro my requirements for video entertainment are fairly minimal, it is just for mental release

OMG... I did not realize that Kurt Russell appeared in an episode of Lost in Space and in an episode of Gilligan's Island.

Both as a young child actor

i loved scifi.

why count potatoes?

what if i told you about a 'space traveler' who gave his only son... for YOU?

at last i will be able to resolve the holy water conundrum

6:39 AM

the feeding of the 5000 was an early preview of the banach tarski paradox

i am sure in austin tx centuries from now, people will diligently study ELONs tweets with reverence

i have used that banach tarski line at a (mathy) party but nobody responded

tech folks are rarely good at double entendres

i suspect there is a cultural element as well

having to communicate in english without being understood by English

dang, thought i had a convex psq, but it was NON-convex-optimisation. what is wrong with people?

i will start a full time position on wednesday. it feels like the end of life.

7:38 AM

@copper.hat tenure track?

8:04 AM

@AbstractSpaceCrack I'll get there in due time. :)

For a matrix, column rank =row rank.
Let A be an m by n matrix. Applying elementary operations on A to get RREF(A)=R, it is noted that row rank r= n- z, where z= dimension of null A.
Let $T \in L(F^n, F^m)$ be defined as Tv= Av. Then, range T= col(A) so rank T=column rank A=c. So n-z=c. This alogwith the earlier equality gives r=c.

Is there any way to avoid the first part?

row rank (A):= number of non zero rows in rref(A).

8:31 AM

@Koro you mean you don't want to use rref?

one potato two potato

I prefer elementary column operation for that argument

there are two other proofs on wikipedia @Koro :

Rank (linear algebra)

In linear algebra, the rank of a matrix A is the dimension of the vector space generated (or spanned) by its columns. This corresponds to the maximal number of linearly independent columns of A. This, in turn, is identical to the dimension of the vector space spanned by its rows. Rank is thus a measure of the "nondegenerateness" of the system of linear equations and linear transformation encoded by A. There are multiple equivalent definitions of rank. A matrix's rank is one of its most fundamental characteristics. The rank is commonly denoted by rank(A) or rk(A); sometimes the parentheses are not...

@CalvinKhor Thanks. I pick the one using orthogonality argument :).

one potato two potato

Orthogonality argument works for inner product space

yeah i think that one is written nicely

8:43 AM

@onepotatotwopotato :(

But considering that every vector space can be equipped with an inner product, that should be fine, I think.

one potato two potato

Every vector space has an inner product?

Actually, I’m not sure. That’s why I added I think also.

:(

9:49 AM

I don't understand why the following was deleted:

math.stackexchange.com/q/4370572/104041

Please help me undelete it.

@Shaun it was deleted by roomba (posts with <0 net votes are periodically removed)

I see. Thank you, @CalvinKhor. Please would you help me undelete it?

@Shaun have voted to undelete. The comment in the revision history is "Scheduled: RemoveDeadQuestions". This link has some information about automatic deletion

Thank you, @CalvinKhor :)

@Shaun yw

10:10 AM

5

Q: Find the limit of $4^n a_n$, for the recurrent sequence $a_{n+1}=\frac{1-\sqrt{1-a_n}}{1+\sqrt{1+a_n}}$

Given the recurrence relation $$ a_{n+1}=\frac{1-\sqrt{1-a_n}}{1+\sqrt{1+a_n}} $$ which is easy to find $$ a_n\to0, \quad b_n=\frac{a_{n+1}}{a_n}\to\frac1{4} $$ hence $a_n\sim4^{-n}$, or with some regular conditions we may prove $$ \lim_{n\to\infty} 4^n a_n = C(a_1) $$ where $a_1$ regards to the ...

sequences-and-series limits

2 hours later…

11:52 AM

Are algebraic cycles also a subvariety? If yes in what sense? The sum is the union? and coefficients the multiplicity?

A plate of momos

12:21 PM

Do you guys think this question is on topic? math.stackexchange.com/questions/4460463/…

12:31 PM

@Aplateofmomos 1) idk what is a 'discrete expression'. 2) this should not be tagged solution-verification. If anything, it should be tagged big-list (and these questions are harder to ask on MSE) 3) have you seen A=B?

A plate of momos

12:58 PM

You know the type of sums you find in a discrete math book

nop

@Aplateofmomos then you should really click the link. A lot of these problems are completely solved

A plate of momos

I want an algorithmic step wise sol ver

similar to how like Integral solver does it

1:55 PM

@Aplateofmomos Again, you should read the book...

they describe how a computer can spit out the answer + a proof certificate which a human can use to prove the result by hand

Karl Kroningfeld

2:55 PM

@Jam Depends on definition of variety, esp. in regards to irreducibility. Effective algebraic cycles are certain closed subschemes of the ambient scheme, and in this case you do recover the interpretation of linear combination = union with multiplicities. You might first consider the case of divisors on curves to hash this out.

3:52 PM

Hi @Karl

A plate of momos

4:15 PM

Oh I was looking for something a bit more accesible @CalvinKhor

4:46 PM

@leslietownes I take a WordPress Starter, at this date there is not any edit since I need learn about it, but my site will be MathOverture (my current doman is mathoverture.wordpress.com). Many thanks.

cool name!

Morning, Munchkin's pet.

hi ted. anything new?

Nah, just finished backing up stuff from the computer and restoring pictures that I messed up somehow. Off to the duck pond?

@leslietownes I am not sure if that question is even remotely worthy for mathoverflow. It will probably be downvoted to oblivion for being way too basic. I still added a 100 point bounty as a last resort.

5:01 PM

Did you think about the question I asked you, @Prithu?

@TedShifrin yea.

Do you have an answer?

Nope

ted: wife is getting a covid test this morning due to an exposure on wednesday. then library. then, undoubtedly, duck pond. maybe after nap time.

I hope the test is negative. Rates are going up crazily again. I'm still masking when I go shopping or anywhere enclosed.

@Prithu: Start with a function that takes on every value once. Can you replace the part of the graph over $[a,b]$ with something interesting and then glue back to the original function?

5:04 PM

some a-hole attended a party at which people later tested positive for covid, and he knew this, and wasn't feeling well, and still attended a one-hour meeting in my wife's office.

they were both masked, but no ventilation.

Selfish brat.

But we're in a time where even those of us with allergies worry about whether we need to test for covid every day.

my wife has been masking at home and we crack a window open in the bedroom.

yeah, haha, the pollen was out of control the other day.

@TedShifrin you mean as a way to generate new constructable sets?

Yes, precisely.

@leslie Today's Wordle was sneaky. Took me 4.

@TedShifrin hmm that is one thing we can do. However i am also interested in finding sets which cant be constructed.

5:10 PM

it was what i call a "comfy 4." it took me 4, but low stakes. knew what it was at that point.

Specifically, my current minigoal is to find a set with odd maximum that can't be constructed.

Well, my approach is a tangible start.

Are you allowing $0$?

we had a great coyote encounter yesterday. we were on a walk and heard a bunch of angry crows. we diverted from our usual walk to see what the crows were angry at. it was the coyote.

@leslie Well, I made the wrong choice when I got four right on guess 3.

we saw him again at the end of the walk, in his usual place behind our house.

5:13 PM

Those crows know what they're crowing about.

@TedShifrin you mean do i allow things like {0,3}?

Yes, or $\{0,1,2\}$, which is easy.

So one thing with $0$ is having horizontal asymptotes (or a global extremum) ... Are you ruling that out, or thinking about it?

@TedShifrin is there any value occuring at that asymptote?

Horizontal asymptote, not vertical.

@TedShifrin then it is 0.

5:35 PM

And for everything above/below it, also.

@TedShifrin yea.

6:00 PM

@leslie @robjohn @copper Here is a good one for you. Have you seen this abbreviated notation anywhere before?

heavens no.

Ninad is talking to me like everyone uses it ... :D

i mean, OK, do that in your office with the door closed. but not in front of students who are likely to ask questions involving it.

yikes.

Well, it's analogous to $x^{-2}$, isn't it?

Xander Henderson

@TedShifrin That's gross.

6:04 PM

I mean, we don't write $(x^{-1})^2$ or $(x^2)^{-1}$. So I see the logic.

but there's arithmetic on numbers. there isn't arithmetic on T.

But I literally have never seen it anywhere before this in 50+ years.

imagine if they did that with a star or dagger as you sometimes see.

i dunno, in my own niche, we'd often be considering semigroups and have all kinds of variables in the exponent.

don't need to make life worse.

Well, why not $A^{-*}$ ? :D

Xander Henderson

$A^{-\top\dagger\ast}$

6:05 PM

you're being me right now. is this what dealing with me is like?

Only the tip of the iceberg, @leslie.

this explains why my wife has that look on her face all the time

What do you mean by arithmetic?

I wonder if anyone will answer my question about where that notation appears/is used.

Xander Henderson

@TedShifrin I would imagine not, as the question has an answer.

No incentive for the asker to engage any further.

6:07 PM

The asker and answerer appear to be German and Polish, and Ninad is from India somewhere. So maybe it's just the US that is so naïvely ill-prepared?

yai: numbers can be multiplied together, and in particular multiplied by -1. so if a and b are numbers it's not unusual to see (x^a)^b = x^(ab) = x^(ba) because there's an operation on numbers in which ab and ba both make sense and we're used to seeing them.

You raise an excellent point, @leslie. I think we should write $A^{\top -}$.

it's bad to write every conceivable form of function composition as if it were arithmetic. it gets confusing quickly.

No wonder so many students struggle with math. shrug

Xander Henderson

@leslietownes My students tell me that everything is linear. Similarly, everything is a number. So arithmetic should be fine, right?

6:10 PM

we do do a lot of that in operator theory, but we know our limits, don't we?

Only for closed operators.

Xander Henderson

@leslietownes Epsilons and deltas, or do you do something a bit more topological?

No, operator calculus, I assume he means.

Xander Henderson

@TedShifrin I was trying to pun. :(

Or make a bad joke.

Or something.

:'(

Oh, I was thinking about the first half of the sentence, not the second. Get thee to a punnery, forthwith.

6:12 PM

in the dynamics realm a function can be both a multiplier on functions or something you pre or post compose by. while any one of them can optionally be denoted by juxtaposition, ideally none of them should be if you're using them all at once

That run-on sentence gave me a migraine.

i haven't gotten a text from the covid test. this makes me nervous.

Isn't the quick one no different from doing a home test? The other one takes a few days.

Or for me it always has.

it should be, but we didn't have a home test. we ordered them and they didn't arrive.

Oh, geez. I have a bunch sitting here. Have Munchkin fly down and get one.

6:14 PM

i thought she was getting the quick test, anyway. we had sunday plans contingent on the outcome. maybe i'm confuzzled.

I'm not convinced that the quick one is all that great. My roommate took it when he was deathly ill (the night before we went to Urgent Care in the morning) and it didn't register.

yes, my impression is that they suck. they pass the 'better than nothing' test but little else.

It got worse. The answerer condescended to prove "the formula" to me. Good grief.

I really think MSE has gone markedly downhill the last few years. All COVID?

Ninad has expanded the discussion to include range/image/codomain. :D

He's suggesting it's regional within the US :D

Xander Henderson

@TedShifrin Lies.

6:30 PM

Soon some robot is going to tell us to take the debate to chat.

Notations change from time to time.

Apparently, no one wants to give me a source that uses that linear algebra notation.

Just because students write nonsense on their papers, that doesn't constitute a change of notation. Some people also write $\int_a^x f(x)\,dx$; that doesn't make it valid notation.

It's like saying "between you and I." Plenty of people do it. Does that make it "correct"?

Anyhow, this has now ascended to one of my pettest of my peeves. So I should go do my back exercises.

Still no source cited. shrug

there's a fair middle ground. you get to use that notation if you don't ask questions involving it (and largely depending upon an understanding of it)

Well, as I brought up the $0\in\Bbb N$ debate ... This may be a question of national convention. I just would like to see an example in print.

I'm sure some teachers have used it in their classes and students then propagate it without knowing it's unusual.

maybe there's some engineering math book somewhere that does it. i could see it happening in a textbook whose purpose is not to teach math.

the idea that someone writing a math book would do that, uh, less plausible.

6:35 PM

Certainly there are enough different notations for the derivative of a function: $D_af$, $Df_a$, $df_a$, etc., etc.

if only because the exercise proving that it makes sense is likely to be a homework exercise in those books, and you don't structure a text to depend on solutions to assigned problems

Xander Henderson

@TedShifrin Linguistically? Yes. But notation is not the same thing as natural language. :D

And tangent spaces: T_pM, TM_p being the obvious ones. I know some people get really confused trying to distinguish $df_p$ from the one-form $df$ and its value at $p$.

Wikipedia says that $0\in\mathbb N$ is in ISO, but I do not plan to pay to check that.

@XanderHenderson That's sort of an interesting question. Is there really any philosophical difference?

Xander Henderson

6:36 PM

@Yai0Phah Since when do mathematicians care about ISO?

What is ISO?

yeah, i can't think of anything more irrelevant to math than a standards organization.

that is itself a type error

Throwing around abbreviations.

Xander Henderson

@TedShifrin I think of it as the difference between informal spoken language and formal written language.

But the distinction is, probably, minor.

If a large group of mathematicians started using $A^{-\top}$, then it would become correct.

I see. Well, much as I love to be a pedant regarding syntax, there's no arguing that lots of grammatical nonsense has become normalized by common usage.

Xander Henderson

6:38 PM

But at this moment in time, with a general mathematical audience in mind, that notation fails to effectively communicate, and is therefore wrong.

nobody has suggested the superior notation, which is, of course, $A^{\perp}$

How do I write the inverse of $A^{-\top}$? $A^{-\top -}$?

Oh, that could never lead to any confusion.

Xander Henderson

$A^{--\top} = A^{\top}$ :P

ted: you'd write $A^{\perp}$ upside down.

This reminds me of the exercise to prove that concatenating closure and complement can lead to at most 14 possible sets.

Xander Henderson

6:39 PM

That's obviously always true, because everything is linear, and all operators are arithmetic in nature.

I forget whose theorem that is. I learned it as an exercise in Munkres.

Xander Henderson

@TedShifrin I really like that exercise.

kuratowski's theorem.

Xander Henderson

And yes, that's where I learned it.

Right.

I had two students in all my years of teaching who absolutely nailed it with beautiful, efficient proofs.

I never figured it out when I was a student, only when I started teaching.

I think their beautiful proofs didn't make it to my scanner when I threw out my office.

Xander Henderson

6:40 PM

I figured it out, but I doubt that my proof was very efficient. I seem to recall it taking up a couple of pages. I am often overly verbose, but that is a lot, even for me. :/

Well, the answerer just finally realized what I was ranting about and said it was "strange notation" and changed his answer!!!

I still remember the two students who gave me those superb solutions. One got a Ph.D. (at MIT) and then quit math. The other pondered doing a Ph.D. but ultimately decided not to.

The key thing is to prove a lemma that establishes periodicity.

i wonder if there is some relation between kuratowski's theorem and grothendieck's 14 natural norms on tensor products of banach spaces.

i detest hero worship in all of its forms and specifically of grothendieck, but his work in banach spaces was really good. and weird.

Stranger things have happened.

How many distinct completions do these norms lead to?

grothendieck himself didn't work out the relations between them. and in particular examples it might be an open problem. i'm not sure it is fully understood.

6:49 PM

I heard once about projective and injective tensor products.

Xander Henderson

@leslietownes I concur regarding hero worship, but that doesn't prevent us from acknowledging the good work that people do. For what is it worth, I find the worship of Newton and Gauss to be much more annoying. :D

I even forget the generality about these tensor products.

i think it's pretty clear you can't use the algebra of abstract relations satisfied by the various operations used to generate the 14 norms, to deduce more relations than grothendieck was aware of.

Maybe they are defined for any locally convex TVS's.

@Xander I confine my hero worship to 20th century mathematicians :)

6:50 PM

xander: somehow it's less annoying to me if they're long dead.

if people you might be working with have could have had very negative experiences with someone people unthinkingly worship, it's a lot worse.

Xander Henderson

@leslietownes Sure. Though the "Gauss as Chuck Norris" memes which popped a few years ago were STUPIT.

@leslietownes Indeed.

@Xander: Well, it wasn't a bot. Now Ninad has created a chat. I'm just wanting an answer to my question, not a long debate. And now the answerer is on my side, anyhow.

whenever i'm about to praise anybody i try to think, "what if it came out tomorrow that they were a sex pest," or whatever. it doesn't change what i say or write because i am not naturally effusive.

but i think others would do well to remember that kind of thing

If I remember correctly, I also saw ${}^t\!A$ for the transpose before.

Xander Henderson

Exactly. Though I am also a proponent of separating the work from the individual where possible.

6:52 PM

Yes, Yai0, that is somewhat common.

xander: "Chinatown" is one of my favorite movies. nuff said.

I suspect people did that so that they could write $^t\!A^{-1}$ :D

Xander Henderson

@leslietownes Yup.

I never do it because it's a pain-in-the-a** to typeset, among other things.

It doesn't help with the left-to-right issues with $(AB)^\top = B^\top A^\top$.

people often only focus on the negative side of separating the work from the individual, i.e., the individual has done something obviously wrong and uh oh, what now. people are less likely to perform this prospectively. e.g., not to automatically assume that someone who created good X is a good person, when there is utterly no known reason to believe otherwise.

i try to practice it all of the time.

6:55 PM

No one has ever assumed I'm a good person.

this is why i do not publicly praise ted shifrin. i don't know what skeletons he has in his closet, but i'm sure there are a lot of them.

Just ask the students who wrote scathing teaching evaluations.

i heard one time ted was on probation for giving too many Fs.

You do try to spread that rumor.

I had an Honors student once who'd been told that faculty needed to have special permission to give grades less than B in an Honors course. Hint: It was not correct.

i told one of my wife's colleagues this about my wife's postdoc. my wife didn't even teach during her postdoc.

Xander Henderson

6:57 PM

Friends, Romans, and countrymen! I come to bury Ted Shifrin, not to praise him!

Why is a Roman burying a Russian?

These days, I suppose, I shouldn't admit my heritage.

they're all versions of the rumor that if the instructor doesn't arrive within x minutes, class is officially canceled.

i appealed to this when i was in the office last week. we had a lunch outside. the building lost power and none of us could get back in. i said, if it doesn't come on within 10 minutes, we're officially off for the day. that's the rule.

people liked this rule.

Xander Henderson

@leslietownes I've told my students that if I am more than 180 minutes late for class, they are free to assume that class is canceled.

haha.

I also had a student who earned a D or F (I forget how generous I was) in the Spivak Calc with Theory class and raised a stink that I'd promised them that if they could do all the standard calculus material correctly they'd get (at least) a B. She forgot that the first time she got the chain rule right was on the final.

It wasn't a pretty story.

6:59 PM

two people who were more senior than i am actually went to their cars in the parking lot after i announced this rule. i am persuasive.

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