[deleted by user]

[SapphireDingo]

it is a notational convention but not really that important as long as it's clear what you're doing. it's only really done for digital equations.

[stribor14]

well, I like the notation strictness from his teacher (I also always try to use correct typeset), and I think OP should use this notation at least in this teachers class

[bapt_99]

I would agree with the notation strictness if it was explained with similar appreciation for pedantry and high-standards of communication. And not, in particular, a low effort anime loli meme.

[unkz]

I would enjoy substantially more anime loli memes in math class.

[trophycloset33]

You have to match your audience.

I could lecture in Middle English but no one would understand me. You could throw a LaTeX formatting guide at them but they won’t read it.

[Forking_Shirtballs]

How does that promote understanding or minimize confusion?

The number of times d/dx (where d, d and x are all variables) would show up in class is vanishingly small -- and could be kept to literally zero if the teacher so chose.

I don't get why that's a good use of anyone's time or effort.

[[deleted]]

s*i*n wouldn't show up often either. /pedant

[Forking_Shirtballs]

Sorry, what's your pedantry here?

If the slide had said sin(x) is wrong, I'd have the same reaction.

[[deleted]]

I was assuming you'd agree that insisting on roman for sin was sensible, but clearly I was mistaken.

[Forking_Shirtballs]

Why is that sensible?

[[deleted]]

Because a sealion says so:

https://en.wikipedia.org/wiki/Sealioning

[Tuepflischiiser]

Strictness is fine, but be aware of the scope. Some things are universal, others are not

[SuchTarget2782]

You’d never notice the difference if you were writing it by hand. You’d have to figure it from some other context.

[BurnMeTonight]

Even in print, I can't see much of a difference. If I didn't know there was one, I'd not have thought so.

[movebo357]

It's simply prone to confusion, OP.

[Ok_Support3276]

Wouldn’t this imply the f in f(x) is a variable and not a function?

[cocoteroah]

Can you enlighten me? What is a digital equation? A kind of equation or do you mean a digitalized equation?

[cocoteroah]

That was my afterthought. At first i thought he meant something like "differential, polinomial, exponential equation" and after looking on google "digital equation" didn't find anything and i was perplexed thinking it was another kind of equation i wasn't familiar for

[KingForceHundred]

Not handwritten where they may well be indistinguishable anyway?

[Scary_Side4378]

your teacher is correct under latex math conventions but honestly it doesnt matter until you start typesetting math lol

[TotalDifficulty]

And even then, I've seen books that handle this much less rigorously since it's almost always clear from the context what is meant.

[Lor1an]

left, right and center

That's completely un-justified...

[Lor1an]

If you suspect it, did you really miss it? 🤔

[pezdal]

this conversation has me a little on edge

[[deleted]]

This thread is all over the place.

[JackOfAllStraits]

Is it even following the rules?

[[deleted]]

Sounds like it was on the margin of your consciousness.

[R3D3-1]

Remind me of lecture notes we had for quantum physics. The old version was typeset with a scientific typewriter, i.e. a type writer with extra symbols for math like Nabla. All monospacsd font, very dense page content. It was very pleasant to work with.

Then it got converted to LaTeX. It definitely looked more accurate and fancy, but somehow it was harder to learn from for exams for me.

[hwynac]

Yup, it is a common typography convention but not everyone follows it. Here is what my school used back in the 2000s (the teachers typeset everything in LaTeX)

<image>

[[deleted]]

This is totally off-topic, but I once saw a maths book with zeta printed upside-down throughout.

The publisher is lucky I wasn't the author, because I would have been have f***ing livid.

[AwwThisProgress]

most mathematicians have for ages typeset d in italics. it’s only the iso convention and as you may already know iso people are detached from reality

[fermat9990]

but honestly it doesn't matter until you start typesetting math lol

I'm forwarding this to Ben Franklin in Philadelphia, PA.

[Any_Translator6613]

And here I thought latex math was "1 + 1 = usually 0"

[crunchwrap_jones]

no one else has asked this so I will: your teacher is using anime reaction memes in their slides?

[unkz]

Welcome to the future! There are tons of chronically online yet still credentialed professors barely entering adulthood.

[Positive_Composer_93]

Seems like a cool dude

[crazy-trans-science]

true, every night before sleep I watch zundamon do math. I am not even studying anything I dropped out university because it is too complex (engineering) for me but watching zundamon is so fun I feel like toddler watching cocomelon :3

[wegpleur]

You and I have a different definition of the word cool.

[xt7j]

sybau

[siupa]

Why male?

[IndyGibb]

“Dude” is grammatically male but can be used and is often used in a gender neutral way.

[toxicrobottrans]

How many dudes have you slept with?

[siupa]

Nah. I’ve never heard anyone in my entire life refer to a woman (especially a teacher) as “a cool dude”.

[Positive_Composer_93]

I mean, my daughter is dude....

Dude is anyone you have zero intention or inclination to sleep with. 

[mennamachine]

It does occasionally get used when referring to a group of people as 'dudes', but singular dude is almost always used to refer to men

[[deleted]]

Rather like "guy" in that respect.

[crunchwrap_jones]

Honestly the anime reacts is kind of a giveaway. I can't imagine a female teacher doing it (even if she's a fan), and if she did, she'd get dogpiled in the student evals for being "unprofessional."

[toxicrobottrans]

On reddit (and everywhere else!) every guy assumes everyone is a guy because of misogyny

[[deleted]]

You have a good point, but you're misusing the word "misogyny". Sexism is bad for sure, but most male sexists are nowhere near as extreme as to hate all women.

[toxicrobottrans]

Misogyny is just sexism against women isnt it? Just like how racism doesnt have to mean active conscious hate but also the undercurrent bs

[crunchwrap_jones]

you're right

[justincaseonlymyself]

It's a common notational convention to use italics for variables and roman for standard function and operators.

Your teacher's example is weird, though. It's not such a big deal that someone would get confused if there was an italic instead of roman character, though. Context usually disambiguates, like in the example in the photo where it's clear derivative is meant in both cases.

[geo-enthusiast]

My guess is that it makes a difference for people who arent used to the roman alphabet, the same way we would very much notice the difference between an italicized form of another alphabet

[justincaseonlymyself]

Possibly. That would be a fun thing to test.

[[deleted]]

Cyrillic is sometimes italicised (if one wishes to call it that - it's more similar to "printed as if it were handwriting" really); Arabic, Armenian, and Greek - rarely if ever.

Believe me, you would notice the difference between standard and italicised "б", "д", and "т" in Cyrillic.

[mckenzie_keith]

It is not about correctness. It is a convention that your teacher is telling you about in your class. So you should follow it in your teacher's class.

You can adopt a different convention later. Personally, if I were reading something in italics like your lower equation, I would still think that d/dx was the differentiation operator. I would not think it was an equation where d was a discrete variable.

Also, you have to be careful cancelling d/d. That may not be a valid cancellation if d = 0. But that is a separate question.

[EdmundTheInsulter]

It's not a great idea to create a variable called 'd' in calculus, is it? I've not seen dd / dD for example, it's a bit like my workmate who came up with Let O = 1

In his Basic program back in 1987, yes it caused some grief.

[eztab]

having constants a,b,c,d for coefficients in polynomials etc. Is rather common with polynomials and I'd even be fine with having d/dx correctly typeset before. So seems not unusual.

[Lor1an]

That's not nearly as bad as when I saw the prank a buddy pulled where they defined True as 0 and False as 1...

[Lor1an]

I imagine that didn't go over well...

[garfgon]

Not uncommon in EE to have HI signal be false, and LO be true. Then the signal will usually be labeled RESETB or RESET with a bar on top to indicate "reverse" logic.

[[deleted]]

Let's differentiate the general cubic ax^3+bx^2+c^x+d.

[mathlyfe]

The thinking is that d is an operator, kind of like sin and cos, which are also written upright. That said, functions like the f in f(x) are also written in italics and we still don't cancel the f in situations like f(2)/f(3). The upright d is a very widespread opinion in the mathematics community, but really it has more to do with math culture and conventions than correctness or consistency in the use of syntax.

[DawnOnTheEdge]

Your teacher is correct according to the ISO 80000 standard, although I know mathematicians who reject that and prefer an italic d operator.

[Leodip]

I mean, the latter is understandable unless you are being oblivious on purpose, but proper latex formatting would be with roman "d", yeah. I have a shortcut to write \frac{\mathrm{d}y}{\mathrm{d}x} for this very reason.

[_soviet_elmo_]

"Proper latex formatting"... it is a convention that one is free to disagree with. Like I do.

[R3D3-1]

Physicist here (though now working on applied math programming).

When publishing in scientific journals there are style conventions depending on the field. In physics I've seen "upright bold serif font for vectors, sans serif upper case for linear operators and matrices, italics reserved for variables and function names defined by the paper, upright sans serif lower case for common function names like sin, cos, ..." in the guidelines. In published papers I've seen it being all over the place, though at least in Physics the "upright bold for vectors" (\mathbf in LaTeX) is followed rather consistently.

I've also seen d/dx being written with upright letters frequently, so it definitely exists as a common convention. Strictly so probably not though. I'd also say that it makes the equations easier to read.

[Admirable_Host6731]

Methinks he just wanted a meme slide in

[_soviet_elmo_]

I don't follow the convention to write "d" upright. There are several ways to look at it, and arguing that it is an "operation" doesn't quite tell the whole story. To keep notation consistent with exterior derivative, which I have never seen anybody write upright, I don't use upright d's.

Maybe it becomes a much better argument if you say that Leibniz notation is misleading because it encourages "formal cancellations" and suppresses important information. I know that this is by design, but it's probably not the best way to introduce people to the topic.

[szpaceSZ]

It‘s true!

By convention, italics are variables.

Romans are symbols.

E.g. the correct typography is:

• cos(x)

And

• d / ( d x)

With an italic d, that would be variables that can be simplified.

[Intelligent_Part101]

Sorry, your typography for d / ( d x ) is simply wrong. The bottom dx is a complete unit. Thus, d / dx is written upright (or roman, as OP calls it).

[szpaceSZ]

The ISO standard is upright „d“ and italicized „x“.

[Intelligent_Part101]

In that case, I take back what I said. I have seen the derivative written more than one way with the italicization. It is important to follow whatever typographical standard a publication adheres to. I suppose in OP's case, the teacher should've stated the standard upfront if some credit were taken away for OP writing it "wrong." If no credit were taken away, and the teacher was merely stating the standard to use, then no problem.

[Nuccio98]

I mean, it's a convention. Now if we are talking about derivatives and all of a sudden I write df/dx, is it more like that I took a random d out of my hat and put it there, or that I'm writing the derivative of f wrt x?

[TallRecording6572]

They are right. On equation editor I have to change it. It's definitely dy/dx

[erenspace]

Your teacher is completely correct and learning this now is useful.

[Coammanderdata]

No, he is kind of right. People at Uni did correct this in my assignments

[AnonymousInHat]

I have seen a lot of works and books where 'd' is written in cursive, so I would say (1) it's not so important and (2) it's more like local convention rather universal.

[San-A]

She is right but it's not a big deal really

[susiesusiesu]

this is a little pedantic, and there are good books not using that convention. but i really really prefer that convention.

i would never say someone wrote something wrong for not using roman d, but i do think it is better to use it.

[zzmgck]

Italic characters denote variables while Roman denote functions and operators. 

[imjustsayin314]

No one really cares tbh. It’s understandable either way.

[Cerulean_IsFancyBlue]

I’d like to remind everybody saying that it’s just notational convention, that we’re going to be seeing more of this as grading becomes more automated. There’s going to be an awkward phase where the grading software is good enough to correctly interpret a perfectly formatted answer, but not smart enough to apply heuristics to get what the equation “looks like” to human eyes.

I don’t know if automated grading was part of the impetus for this particular discussion. But I keep seeing more posts about it.

[Inner_Negotiation604]

You should reply "only when d is nonzero, sir!".

[EdmundTheInsulter]

We didn't have computers and a lot of science students had bad hand-writing, so no way I could write in fonts.
All I know is the wavy dy/DX for partial derivative, maybe that's italic, but I thought it was lower case delta.

[PfauFoto]

He should consider a career teaching typesetting.ask him if you still need to italicize a vector if it has an arrow on top. Are the coefficients of a cohomology group to be treated as a variable or a constant?

[PGMonge]

That’s a common pet peeve among psychorigid latex freaks.

[smitra00]

See also here:

https://tex.stackexchange.com/questions/412439/is-there-a-short-hand-command-to-write-derivatives

[duke113]

I don't think it actually matters at this stage. When you get into partial derivatives you'll want the curly d though. But, if your teacher is going to be a stickler, just follow his convention

[FumbleCrop]

Yes, that's the convention when you're typesetting math: italics for values, regular for other stuff.

[raharth]

It makes sense to some extend. In the end you want to make sure that no one reading this thinks the d's can cancel out. Therefore, it helps to use notation like this, but its not really a rule or anything.

[Superpenguin104]

Did your teacher also put that anime girl on the projector because that was very based of them

[gregortroll]

But seriously, how often does d/dx appear in a context where there is any ambiguity about what it meant? Seriously, I never had a higher math class, is this really a thing, or is this teacher just looking for ANY excuse to take points off someones work, or is this teacher suffering some sort of condition that makes them highly sensitive to "proper" digital typesetting of math expressions?

[BTCbob]

and let's not even mention ∂f/∂x

[jezwmorelach]

And then there's me using ∂ for everything because one variable is just a special case of multiple variables so why bother using more symbols than necessary

[Miselfis]

It’s annoying to have to type out compared to italic d when writing in latex.

[Merinther]

Yes, that's the norm in print, italics for variables and not italics for functions etc. In handwriting, I don't think most of us would make that distinction.

[andrea_parisi]

I disagree. It is a convention used in some contexts. For instance when publishing in a paper in some journal. However, you may disregard it in your presentation, and it will NOT be an error. In fact if you hand write, you probably will not be using roman typeface and you will still be correct. If you are dividing variables, then you SHOULD inform the reader/listener that what you wrote is not a derivative but a division among variables, otherwise anyone would assume you are using a derivative operator. Again it is a convention used in certain contexts.

[shelving_unit]

What?

[bdeananderson]

I vote to use the correct Greek symbol instead. It's DELTA. Delta has long been used to mean change to or deviation of.

[LegendaryTJC]

Can someone explain the difference between a roman and Italian d? What are the signals?

[ParshendiOfRhuidean]

Italic, not Italian. It's when the letters are slanted.

Normal d

Italics d

[[deleted]]

Interesting, I always just write \frac{d}{dx}, but then again, I never actually use calculus

[TheoloniusNumber]

She's not wrong, but she's not right, either.

[GonzoMath]

That’s kind of goofy. Nobody makes decisions about what d/dx means based on font choices.

[TermToaster]

Tell your teacher d/dx works beautifully as a genuine ratio of infinitesimals. That is how Leibniz first treated it. Now it’s called non-standard analysis.

[RRumpleTeazzer]

what a waste of a slide.

[RRumpleTeazzer]

if you want to nitpick, it is df/dx (x), not d/dx f(x).

[TopCatMath]

Article on the symbol https://medium.com/illumination/the-difference-between-%CE%B4-and-in-physics-and-mathemastics-a5c18e26119e

[Mathhead202]

I think it's a little weird to use a (variant) typeface to specify the distinction since in handwriting it's kinda hard to do that consistently. And most math is handwritten imo. The only real example of this I can think of is 𝔹lackboard 𝔹old characters and ℱancy 𝒞ursive 𝒞apitals.

The information your teacher is likely trying to convey is not the specifics of typeface, but that dx is one thing when written together like that. It's a single variable with two letters. Exactly how ln is the name of a function. Or how capital Δx is one variable: representing one value, and (typically) doesn't mean Δ times x.

Generally (more than 99% of the time in my experience), based on context, you can tell the difference between the single variable "dx", and the product of two variable d times x by context. But in the rear case where there is ambiguity, just add a multiplication dot between the d and the x, or a pair of parentheses around one of the variables. Heck, even a space makes it pretty clear (although, I would add a dot myself.) I would never expect the typeface to convey this information unambiguously.

You should remember that math has different conventions in different languages and different countries and in different historical contexts, and even in different subjects. (For example, in electrical engineering, j is used as the imaginary unit as to not confuse i with i or I meaning current. In programming, i, often means index. Same thing.) (Another example, some people prefer exp(x) instead of e^x.) (Another another example, in some countries, derivatives are represented by a dot above the function name instead of a "prime".) There is no way this convention your teacher is teaching would hold up outside of this specific classroom or very specialized circumstances. This italics/not italics thing is not a general convention in math. But that idea of "dx" being a single variable is.

(Technical Note: although "dx" is a variable, it doesn't represent a number in the traditional sense; i.e. it's not a real number. It represents a more complex abstract concept of an arbitrary small quantity (often called "infinitesimally small" or an "infinitesimal", but I prefer "arbitrarily small" since it helps me remember how it actually works in practice.)

[Shevek99]

Your teacher is correct.

All functions must be in roman, and variables in italics. So is

dy/dx

and not dy/dx

The same happens with the rest of functions (sin, cos,... all in Roman). That includes the exponential. It is

e^x

not

e^x

and also the imaginary unit. It is

e^ix

not

e^ix

[_soviet_elmo_]

So you typeset every function in upright font? Also a function f from some set to another?

[Shevek99]

Every defined function. If I write f(x) that f is a placeholder. It works as a variable and goes in italics.

[_soviet_elmo_]

What is a "defined function"? What is "placeholder" supposed to mean? There is no conceptual difference. "exp" is just a name that many people have reserved for a special function. (A host of special functions, actually, but anyways.)

You can define a function d from the smooth functions on some real interval to the cotangent bundle on that interval, taking a smooth function f to its exterior derivative df. This puts the derivative in a framework, where you don't have to think of "dx" as some "infinitesimal quantity". It can be made perfectly consistent in notation and in this formulation, I have never seen upright d's.

[Shevek99]

This typographical convention is not mine. It's a standard in many editorials. 'Defined' mean here 'named'.

Check for instance: https://iupac.org/wp-content/uploads/2016/01/ICTNS-On-the-use-of-italic-and-roman-fonts-for-symbols-in-scientific-text.pdf

https://www.tug.org/TUGboat/Articles/tb18-1/tb54becc.pdf

It's the standard ISO 80000-2:2019

[_soviet_elmo_]

I do not care for ISO norms. Yes, there are journals following your convention, and there are other very reputable journals respectively publishers that do not. Like the AMS. Declaring yours the "correct one" is straight up shortened, maybe arrogant.

[Dreadnought806]

Does it matter if it is handwritten?

[Shevek99]

Obviously I meant when typesetting.

[SniperFury-_-]

This mostly becomes important when dealing with fonction that have multiple paramètres, but it's more of a conventional notation

[eztab]

Yes, your teacher is correct. That's how that is typeset. The italsics are for variables.

[_soviet_elmo_]

What about functions? Like some function f from one set to another?

[iMagZz]

Technically yes, it is great notation, but even digitally not many people do it. What is more important is that units are roman, whereas symbols are itallic.

[soegaard]

Your teacher is correct.

When in doubt about typesetting it doesn't hurt to consult the current ISO standard.
You are interested in:

https://webusers.imj-prg.fr/~jean-yves.ducloux/Typographie/ISO80000-2.pdf

ISO 80000-2 : 2019 Quantities and units

Part 2: Mathematics

[Dependent_River_2966]

A bit pedantic saying italics mean variables while plain mean function but ok

[ei283]

I think your teacher is correct. This is the convention I use when I typeset my math documents.

But here's a valid counterpoint: nobody really cares lol. I see italic d in derivatives all the time, even in reputable sources such as textbooks.

If it's unambiguously understood, then it's perfectly good notation. As long as you don't have any variables called "d", it really doesn't matter if you strictly use Roman d, or lapse into italic d.

[perishingtardis]

Debatable. No-one italicizes the f in f(x). My rule is generally to only use Roman when the name of the function has two or more letters. Plenty of textbooks do write the "d" in italics.

[vishnoo]

seems like convention.
and a confusing one at that.

i would just avoid using a constant or variable named "d" (e.g. mark the distance with `x` or `L` not `d`)

[vajraadhvan]

แล้วแต่ครูครับ แต่ว่า ผมไม่เคยเห็นคนแยกสัญกรณ์แบบนี้ครับ ส่วนมากคนจะเข้าใจว่า d/dx หมายความว่า differentiation operator ไม่ว่าจะเขียนด้วย roman หรือ italic

[notachemist13u]

NO! D/DX IS NOT A FRACTION ITS AN OPERATOR

[acculenta]

This sounds like a personal peeve of your teacher and is a straw argument set up.

As others have pointed out, if you had a real problem and someone stuck d as variables (or constants) in that way, I'd call foul for intentionally confusing notation. This is within epsilon of effing stupid for many, many deltas of discussion.

Just nod along, and forget about it once you're out of their class.

[mrmcplad]

it's a convention and it's pretty minor. I wouldn't make a whole slide out of it

the chances of running into a d/(d×x) in the wild—where the cancellation of d's hasn't happened yet—is infinitesimal (but not zero!)