# How to use Math tags

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#### Dason

A previous thread covered this topic (found here) but I figured a more detailed explanation could be given to help some people out.

Contents
1. How do I use math tags?
2. Symbols
3. Subscript/Superscript/Other Modifiers
4. Fractions/Integration/Summation/Limits
5. Tables
6. Misc.

0.5) Why math tags? Why not tex tags?

The forum has both math and tex tags. However, the tex tags seem broken and don't properly render a lot
of stuff so we *highly* suggest using math tags instead of trying to get tex tags to work.

1) How do I use math tags?

The forum includes typesetting using LaTex through the use of two special tags:
Code:
$ and Code: $
.

A quick example - The following code:

Code:
$Y_i = \mu_i + \epsilon_i$
produces the following result: $$Y_i = \mu_i + \epsilon_i$$

There are various ways to see the code somebody else used to produce their mathematical typesetting. If you have javascript enabled you can click on their typesetting and a popup will display the code they used. If that doesn't work you can always 'quote' the post of interest and examine their post directly to see how they formatted it.

2) Symbols

There are many symbols that can be produced through the use of LaTeX. There are many guides on the internet that will show you the thousands of symbols that can be created. However, for a quick guide you can refer here or just browse other member's posts. It's not that bad and you can learn quickly. For a quick list of the more commonly used symbols you can refer below:

$$\begin{array}{|l|c|} \hline Code & Result \\ \hline alpha & \alpha \\ beta & \beta \\ epsilon & \epsilon \\ lambda & \lambda \\ mu & \mu \\ sigma & \sigma \\ theta & \theta \\ chi & \chi \\ \hline \end{array}$$
$$\begin{array}{|l|c|} \hline Code & Result \\ \hline cap & \cap \\ cup & \cup \\ cdot & \cdot \\ cdots & \cdots \\ ldots & \ldots \\ \hline \end{array}$$
$$\begin{array}{|l|c|} \hline Code & Result \\ \hline leq & \leq \\ geq & \geq \\ neq & \neq \\ subset & \subset \\ sim & \sim \\ equiv & \equiv \\ propto & \propto \\ \hline \end{array}$$
$$\begin{array}{|l|c|} \hline Code & Results \\ \hline exists & \exists \\ forall & \forall \\ infty & \infty \\ mathbb\{R\} & \mathbb{R} \\ mathbb\{N\} & \mathbb{N} \\ mathbb\{Z\} & \mathbb{Z} \\ \hline \end{array}$$

and there are lots more. Note that you would need to add "\" to the front of any of that 'code' to produce the actual symbol inside of a math tag. That should give you a good start though. Note that you don't need a symbol to to a 'less-than' or 'greater-than' because you already have '<' and '>' on your keyboards.

3) Subscript/Superscript/Other Modifiers

If you want to add a superscript or subscript LaTeX makes it easy. The superscript operator is '^' and the subscript operator is '_'. For example
HTML:
$x^2$
Produces $$x^2$$
and
HTML:
$x_i$
Produces $$x_i$$. It's possible to have both.
HTML:
$x^2_i$
Produces $$x^2_i$$. If you want to have more than one character as part of your superscript or subscript you need to enclose the entire phrase in curly braces i.e.
HTML:
$y^{3x - 5}_{max}$
Produces $$y^{3x - 5}_{max}$$.

There are also other useful modifications one could want to make to symbols. A few of which are adding a bar, a hat, or making something bold. For example:

HTML:
$\bar{x}$
Produces $$\bar{x}$$

HTML:
$\hat{y}$
Produces $$\hat{y}$$

and for when you work with vectors a lot of times you want to make something bold to let people know that it's a vector. We can do something like that by using \mathbf{}. For example:
HTML:
$f(\mathbf{y} | \theta) = \prod_{i=1}^n f(y_i | \theta)$
gives $$f(\mathbf{y} | \theta) = \prod_{i=1}^n f(y_i | \theta)$$

4) Fractions/Integration/Summation/Limits

Fractions

In LaTeX fractions have the same general form:
HTML:
$\frac{numerator}{denominator}$
A few examples:
HTML:
$\frac{7!}{2!(7-2)!}$
Produces $$\frac{7!}{2!(7-2)!}$$

HTML:
$\frac{\beta^{\alpha}}{\Gamma (\alpha)}$
Produces $$\frac{\beta^{\alpha}}{\Gamma (\alpha)}$$

Integration

If you want to write out some formulas involving integration then \int is your friend.
HTML:
$\int x^2 dx = \frac{1}{3}x^3 + c$
Produces $$\int x^2 dx = \frac{1}{3}x^3 + c$$. It's easy enough to add limits to the integration using the superscript and subscripts we used before. For example:

HTML:
$\int_{-\infty}^{\infty} \frac{1}{\sqrt{2 \pi}}e^{-\frac{x^2}{2}} dx = 1$
Produces $$\int_{-\infty}^{\infty} \frac{1}{\sqrt{2 \pi}}e^{-\frac{x^2}{2}} dx = 1$$

Summation

Our example will involve the binomial distribution:
HTML:
 $\sum_{x = 0}^n {n \choose{x}} p^x (1-p)^{n-x}$
Produces $$\sum_{x = 0}^n {n \choose{x}} p^x (1-p)^{n-x}$$

Limits
Limits get their own subsection for the sole reason that not everybody realizes that \lim is a latex command. Notice the difference between the following two examples

HTML:
 $lim_{x \rightarrow \infty}$
$\lim_{x \rightarrow \infty}$
The first looks like this: $$lim_{x \rightarrow \infty}$$ while the second looks much better: $$\lim_{x \rightarrow \infty}$$

5) Tables

When presenting data a lot of times it will look much nicer in tabular form. An example table:
HTML:
$\begin{array}{|l|cr|} \hline ID & Age & Weight \\ \hline Ted & 25 & 180 \\ Frank & 52 & 169 \\ Sue & 32 & 125 \\ \hline \end{array}$
Which will produce:
$$\begin{array}{|l|cr|} \hline ID & Age & Weight \\ \hline Ted & 25 & 180 \\ Frank & 52 & 169 \\ Sue & 32 & 125 \\ \hline \end{array}$$

You must start a table with the \begin{array} command. The portion directly after that (it looks like {|l|cr|} ) is quite customizable. What that part does is control how many columns the table will have, where you will have vertical lines, and how each column is justified. By adding the pipe character (it looks like '|' and is obtained by holding shift and hitting the key above 'enter') you add a vertical line to separate columns. The different letters (l, c, r) stand for "left", "center", and "right" justified. The command \hline tells the table when to add a horizontal line. Once you get to the portion of the table where you're actually adding data you separate the data between columns with the '&' character. You tell the table that you are finished with a row by ending it with two backslashes ("\\"). When you're finished with the table you need the \end{array} command.

Another example:
HTML:
$\begin{array}{|c|c|c|} \hline Parameter & Point Estimate & 95\% Interval Estimate \\ \hline \beta_0 & .503752 & (0.35280, 0.65470) \\ \beta_1 & .002229 & (0.00191, 0.00254) \\ \beta_2 & -1.286 & (-2.5331, -.038942) \\ \hline \end{array}$
$$\begin{array}{|c|c|c|} \hline Parameter & Point Estimate & 95\% Interval Estimate \\ \hline \beta_0 & .503752 & (0.35280, 0.65470) \\ \beta_1 & .002229 & (0.00191, 0.00254) \\ \beta_2 & -1.286 & (-2.5331, -.038942) \\ \hline \end{array}$$

If you use R and want to create a table from some data you might be interested in the xtable package. It will automatically generate the latex code to create a table from your data which can save you lots of time copying/pasting and inserting various symbols.

End Remarks

There is a lot more you can do with LaTeX that went unmentioned. Hopefully you have a decent understand how to use some of the basic math typesetting available to you here.

Other references on how to use LaTeX:
http://www.artofproblemsolving.com/W.../LaTeX:Symbols
http://www.physicsforums.com/misc/howtolatex.pdf

It should be noted that not all features of LaTeX are enabled in this web environment but you should be able to do almost anything you would want to post. If you have questions feel free to ask.

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#### Dason

Re: Suggest Sticky: How to use Math tags

Comments? Suggestions? I can completely change the layout or add/remove sections. I just want to know what everybody thinks.

##### Ninja say what!?!
Re: Suggest Sticky: How to use Math tags

Very impressive Dason. I'm glad that you took the time to post this. Maybe this should be a sticky for the forums.

#### CB

##### Super Moderator
Re: Suggest Sticky: How to use Math tags

Comments? Suggestions? I can completely change the layout or add/remove sections. I just want to know what everybody thinks.
It looks pretty great to me - I've already found it useful. You seem to have the basics well covered, and the layout is very sensible. It might be nice to include the code for $$\bar{x}$$ in the symbols section, since it's probably one that is used a fair bit, although it's easy enough for us to look up symbols like this in the link Sambit posted.

Thanks heaps for putting this together, it's definitely helped to get me started! Now, how do I start persuading people in psych that LaTeX beats Word? #### quark

Re: Suggest Sticky: How to use Math tags

Very nice. I think this would be great for the first two forum categories. We can also make it an announcement so it goes sitewide. What do you guys think?

#### Sambit

##### New Member
Re: Suggest Sticky: How to use Math tags

i think we all should thank Dason for the time and effort he gave for writing this thread by making it sticky.

#### TheEcologist

##### Global Moderator
Re: Suggest Sticky: How to use Math tags

Great, its here! Nicely done and very useful. :tup:

#### Dason

Re: Suggest Sticky: How to use Math tags

Ok. So I added a small part on creating things like: $$\bar{x}, \hat{y}, \mathbf{y}$$ and I added some links at the bottom. If there aren't any more comments or suggestions I think we could probably put this up as a sticky/announcement soon.

#### trinker

##### ggplot2orBust
Re: Suggest Sticky: How to use Math tags

I didn't know this existed. I'll reference posters to here for formatting things like math tags from now on.

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