# Latex question, new line

1. Oct 31, 2008

### Redbelly98

Staff Emeritus
I can't seem to generate multiple lines within a single [ tex ][ /tex ] block. It's supposed to happen if I type \\ but it just never works for me.

Example:

$$f_1(x) = x \\ f_2(x) = 1-x^2$$

The "f2(x)" is supposed to start on a new line.

What am I doing wrong?

Last edited: Nov 1, 2008
2. Nov 1, 2008

### phyzmatix

Unfortunately I'm not going to be of any help to you. I've also tried this numerous times, but to the same effect.

3. Nov 1, 2008

### Hootenanny

Staff Emeritus
I don't think that the \\ has ever worked on the forums, it must be some kind of bug in the software. However, one can start new lines using the flalign environment.

\begin{flalign*} f_1\left(x\right) & = & & x\\ f_2\left(x\right) & = & & 1-x^2\\ f_3\left(x\right) & = & & \frac{f_1}{f_2} \\ & = & & \frac{x}{1-x^2} \end{flalign*}

And the code:
Code (Text):
\begin{flalign*}
f_1\left(x\right) & = & & x\\
f_2\left(x\right) & = & & 1-x^2\\
f_3\left(x\right) & = & & \frac{f_1}{f_2} \\
& = & & \frac{x}{1-x^2}
\end{flalign*}
The * is used to suppress line enumeration. The alignment of each element is fixed to alternate between left and right as shown below

Code (Text):
\begin{flalign*}
right & left & right & ... \\
right & left & right & ... \\
right & left & right & ... \\
\end{flalign*}
But you can add additional & separators to obtain the desired layout, as I have done above:

Code (Text):
\begin{flalign*}
right & left &  & left \\
right & left &  & left \\
right & left &  & left \\
\end{flalign*}
I agree that this method is far more verbose than simply using \\ is mathmode, but it is the only work-a-round that i know of for PF. Note that the eqnarray environment does not display correctly either at PF.

4. Nov 1, 2008

### Redbelly98

Staff Emeritus
Thanks Hoot. So the &'s help line up the equal signs. And if I just wanted to left-justify each line, each line would start with a &.

Code (Text):

\begin{flalign*}
& f_1(x) = x \\
& f_2(x) = 1-x^2
\end{flalign*}

I also found this previous discussion in a locked thread:

However, in chroot's examples the code uses TWO begin and TWO end statements, eg.
\begin{equation*}
\begin{split}

So the single begin statement
\begin{flalign*}
is an improvement over that.

Thanks again!

RB

5. Nov 1, 2008

### Hurkyl

Staff Emeritus
I've never known it to work in LaTeX either. (Remember that [ itex ] ... [/itex] is analogous to $...$, and [ tex ] ... [/tex] is analogous to $...$)

6. Nov 1, 2008

### Hootenanny

Staff Emeritus
Hmm, you're quite right: \\ only works in array enviroments in LaTeX

7. Nov 1, 2008

### robphy

$$\] This is the first line.\\ This is the second line.\\ This is the third line. $E=mc^2$ This is another line. $$$ Click on the rendered image to see what I did. Maybe some $$\LaTeX$$ expert can explain what is going on. I suspect that the forum software already places us in a $$\LaTeX$$ environment... and these \[$ break us out of it somehow.

Last edited: Nov 1, 2008
8. Nov 1, 2008

### cristo

Staff Emeritus
Sounds precisely right to me: the $$tag acts like $and by typing$, you close the latex environment. 9. May 30, 2011 ### Redbelly98 Staff Emeritus Now that we are using MathJax, I am revisiting how to generate multiple lines within a single LaTeX code block. EDIT: Nevermind, I found out how to do this: https://www.physicsforums.com/showthread.php?p=261329 Also, scroll down post #1 here for multi-line examples: https://www.physicsforums.com/showthread.php?t=8997 Please disregard the following... I just now noticed a problem with these old posts (for example Post #'s 1 and 3 above). Right now I see the LaTeX code, without the [_tex_] tags, enclosed in a box and left-right centered in the page. I have FireFox 4 and Windows 7. Apparently MathJax doesn't like the double-backslash newline indicator, and that is preventing the code from being processed properly. Testing: Using same code from Post #1 again: [tex] f_1(x) = x \\ f_2(x) = 1-x^2$$

Same code, with double-backslash removed:
$$f_1(x) = x f_2(x) = 1-x^2$$

So the question is, is it possible anymore to generate a new line within the same [_tex_] code block? Hootenanny's trick in Post #3 used to work -- not that I am advocating going back to the old LaTeX system.

Last edited: May 30, 2011
10. May 30, 2011

### Hurkyl

Staff Emeritus
Here:
\begin{align} a & b \\ c & d \end{align}

This one gives weird results:
$$\begin{multline} a b \\ c d \end{multline}$$