latex align command

[Bruce]

I copy example code from forum's list of latex commands but there's some issue. I can't see how to fix. Example latex shows it's equation pair with aligned equal signs.

[math]\begin{align} a&=b+c \\ d+e&=f \end{align}[/math]


Also noticed
$$\utilde{AB} \text{ and } \widetilde{ac}$$nbd, what this stretched tilde means in math?

 

[BigBeachBanana]

Forum only renders aligned

[math]\begin{aligned} a&=b+c \\ d+e&=f \end{aligned}[/math]


$$\begin{aligned} a&=b+c \\ d+e&=f \end{aligned}$$

 

[Bruce]

Thanks. I guess it's typo in list.....
it says align

 

[topsquark]

Thanks. I guess it's typo in list.....
it says align

There are several "align"-like commands.
align
aligned
flalign
align*

These are the ones I've seen, there may be more. aligned is the only one that works on this forum. (And all of the forums that I regularly visit, anyway.)

As to the tilde, it has a couple of possible meanings. But if it's stretched across several variables, it still has the same meaning. But $\widetilde{ABC}$ just looks better than something like $A\tilde{B}C$.

-Dan

 

[stapel]

Thanks. I guess it's typo in list.....
it says align

Sometimes legacy posts aren't corrected when server software is updated or changed.

To see (much of?) what this forum's math-formatting script can handle, try (here).

 

[pka]

I copy example code from forum's list of latex commands but there's some issue. I can't see how to fix. Example latex shows it's equation pair with aligned equal signs.

[math]\begin{align} a&=b+c \\ d+e&=f \end{align}[/math]


Also noticed
$$\utilde{AB} \text{ and } \widetilde{ac}$$nbd, what this stretched tilde means in math?

using [ imath] (without the space) gives
\begin{aligned} a&=b+c \\ d+e&=f \end{aligned}
$\begin{aligned} a&=b+c \\ d+e&=f \end{aligned}$

 

[Dr.Peterson]

I copy example code from forum's list of latex commands

Thanks. I guess it's typo in list.....
it says align

Which list are you referring to? What is the url?

To see (much of?) what this forum's math-formatting script can handle, try (here).

I suspect this is the "list" mentioned; it includes "align", with this example:

\begin{align}​

a&=b+c \\
d+e&=f
\end{align}​

which doesn't work in either math or imath:

[imath]\begin{align} a&=b+c \\ d+e&=f \end{align}[/imath]

[math]\begin{align} a&=b+c \\ d+e&=f \end{align}[/math]

But "aligned" does work:

$\begin{aligned} a&=b+c \\ d+e&=f \end{aligned}$

$$\begin{aligned} a&=b+c \\ d+e&=f \end{aligned}$$
I guess this is just a thing we have to learn for ourselves? Or is there something in that document that I'm missing, that says certain features aren't supported in our installation?

 

[stapel]

I guess this is just a thing we have to learn for ourselves? Or is there something in that document that I'm missing, that says certain features aren't supported in our installation?

As far as I know, yeah, you just have to figure it out for yourself. If there is a canonical doco somewhere, I'm not aware of it.

 

[topsquark]

As far as I know, yeah, you just have to figure it out for yourself. If there is a canonical doco somewhere, I'm not aware of it.

There's got to be documentation somewhere. (Are we using KaTeX or MathJax here? I've forgotten.) When the program was purchased a readme file was probably included., though that might not be accessible to anyone who didn't buy the program. And it's likely that whoever installed it made further choices as to what could be done and what couldn't.

It's clear that you didn't install it, stapel. Do you know who did? If it was the site owner, it's probably gone forever at this point.

But I agree: the simplest solution is to try something and see if it works. That's pretty much the way I've learned all of the LaTeX that I know!

-Dan

 

[Bruce]

Which list are you referring to?

I used link on the window for entering latex (from toolbar). There is also link in this thread, same as stapel posted, I think. It says katex.org provides latex in the forum, and the link is for supported functions. I see now the list is outdated. thanks

 

[Bruce]

As to the tilde, it has a couple of possible meanings

What are those, please?

Also, post #2 has changed from when I saw it before there were only two lines of latex; now code and explanation is added. Is there forum feature for notifications for updated posts?

 

[BigBeachBanana]

What are those, please?

Tilde -- from Wolfram MathWorld

The tilde is the mark "~" placed on top of a symbol to indicate some special property. x^~ is voiced "x-tilde." The tilde symbol is commonly used to denote an operator. In informal usage, "tilde" is often instead voiced as "twiddle" (Derbyshire 2004, p. 45). 1. An operator such as the...

mathworld.wolfram.com

What are those, please?

Also, post #2 has changed from when I saw it before there were only two lines of latex; now code and explanation is added. Is there forum feature for notifications for updated posts?

It's always been there since the beginning. You probably didn't notice. Otherwise, there would be an edited time stamp at the bottom right corner as you did in post#1.

 

[Bruce]

$\widetilde{\text{many thanks for tilde link}}$

One use is differential operator $\big(\tilde{D}=\frac{\text{d}}{\text{dx}}\big)$
and integration operator $\big(\tilde{D}^{\text{-}1}\big)$

but their examples include this
$\displaystyle \bigg(2-\frac{\text{d}}{\text{dx}}\bigg)^n$
and that looks strange. If d/dx is numerical amount, then why describe d/dx as "operator".

 

[topsquark]

$\widetilde{\text{many thanks for tilde link}}$

One use is differential operator $\big(\tilde{D}=\frac{\text{d}}{\text{dx}}\big)$
and integration operator $\big(\tilde{D}^{\text{-}1}\big)$

but their examples include this
$\displaystyle \bigg(2-\frac{\text{d}}{\text{dx}}\bigg)^n$
and that looks strange. If d/dx is numerical amount, then why describe d/dx as "operator".

What do you mean by "numerical amount"? Unless there's some special use going on there, anything with a d/dx is a differential operator. The symbol d/dx (at least at the Calc I,II, and III levels) has no meaning all by itself... it has to act on a function.

-Dan

 

[Bruce]

It's always been there since the beginning

It wasn't, but noticed yesterday you posted about two minutes before I read. Maybe still finishing the post. Forum should send alerts for that.

 

[Bruce]

What do you mean by "numerical amount"?

When used as a differential, symbol dx is infinitesimally small number. Then, it's not an operator. I'm not sure what their example means by subtracting d/dx instead of dx.

 

[Bruce]

btw, I just edit my post above two times, but there is no "edited time stamp" (I mean, I don't see one)

 

[Dr.Peterson]

btw, I just edit my post above two times, but there is no "edited time stamp" (I mean, I don't see one)

In my experience, you can edit within 30 minutes, and if you do so soon enough (I don't know the definition), it doesn't mark that it was edited, but if you wait more than a few minutes it typically does.

(I edited it after 2 minutes to see what happens.)

(There was no edited date. I'm adding this after 5 minutes.)

but their examples include this
$\displaystyle \bigg(2-\frac{\text{d}}{\text{dx}}\bigg)^n$
and that looks strange. If d/dx is numerical amount, then why describe d/dx as "operator".

You're referring to an example at https://mathworld.wolfram.com/DifferentialOperator.html, right?

The differential operator satisfies the identity​

​

$\left(2x-\dfrac{d}{dx}\right)^n 1=H_n(x)$​

​

where $H_n(x)$ is a Hermite polynomial.​

So you copied it wrong, though that doesn't make a big difference.

They demonstrate after this how the operator is applied; did you try following that?

Here's the idea, in more detail: $$\left(2x-\dfrac{d}{dx}\right)^2 1=\\\left(2x-\dfrac{d}{dx}\right)\left(2x-\dfrac{d}{dx}\right) 1=\\\left(2x-\dfrac{d}{dx}\right)\left(2x\cdot1-\dfrac{d}{dx} 1\right)=\\\left(2x-\dfrac{d}{dx}\right)\left(2x\right)=\\2x\cdot2x-\dfrac{d}{dx}2x=\\4x^2-2$$
In effect, you pretend that $\frac{d}{dx}$ is just a "number" you are "multiplying" by, until you actually carry it out as a differentiation.

It's an operator because it does something to what follows, in this case by differentiating a function.

When used as a differential, symbol dx is infinitesimally small number. Then, it's not an operator. I'm not sure what their example means by subtracting d/dx instead of dx.

No, you seem to be confusing $dx$, which is a differential (for some purposes thought of as a small number) and $\frac{d}{dx}$, which operates on a function. The latter is an operator; the former is not.

 

[Bruce]

pretend that d/dx is just a "number"

Oh, I didn't know the pretend part. I think it strange to write $\frac{\text{d}}{\text{dx}}$ for a pretend number but thank you for showing $\frac{\text{d}}{\text{dx}}$ makes sense as operator after expansion.

I mean, I expect to see $\frac{\text{d}}{\text{dx}}$ followed by function. In $2x-\frac{\text{d}}{\text{dx}}$ it looks like function part is missing, looks like subtracting operator from 2x.

you seem to be confusing dx, which is a differential (for some purposes thought of as a small number)

I said dx is a very small number when used as a differential. I understand operators (except when they mean something else, I guess, lol).

NBD, but the web site changed operator $\frac{\text{d}}{\text{dx}}$ to dxdxdx when I quote your post. I make typos and so does this site!

 

[Dr.Peterson]

Oh, I didn't know the pretend part. I think it strange to write $\frac{\text{d}}{\text{dx}}$ for a pretend number but thank you for showing $\frac{\text{d}}{\text{dx}}$ makes sense as operator after expansion.

I mean, I expect to see $\frac{\text{d}}{\text{dx}}$ followed by function. In $2x-\frac{\text{d}}{\text{dx}}$ it looks like function part is missing, looks like subtracting operator from 2x.

What I meant by "pretend" was that you treat it as if it were a number. Yes, it is strange in most contexts; and in fact you can't do anything until it is next to a function!

NBD, but the web site changed operator $\frac{\text{d}}{\text{dx}}$ to dxdxdx when I quote your post. I make typos and so does this site!

That's not exactly a typo; it's a common error that various sites make when you cut and paste LaTeX, in which they give three different forms of the same thing. This site handles it fine when you Reply to an entire message, but messes up when you select a part and Reply to that (or when you copy and paste. Knowing that, I Replied to your entire message twice in what I just wrote, and removed what I didn't want. Here is what happens if I Reply to just your first line,

Oh, I didn't know the pretend part. I think it strange to write ddx\frac{\text{d}}{\text{dx}}dxd for a pretend number but thank you for showing ddx\frac{\text{d}}{\text{dx}}dxd makes sense as operator after expansion.

and here is the result of pasting it:

Oh, I didn't know the pretend part. I think it strange to write ddxdxd for a pretend number but thank you for showing ddxdxd makes sense as operator after expansion.​