Matrices

1. Use $$\begin{matrix}…\end{matrix}$$ In between the \begin and \end, put the matrix elements. End each matrix row with \\, and separate matrix elements with &. For example,

   $$
   \begin{matrix}
   1 & x & x^2 \\
   1 & y & y^2 \\
   1 & z & z^2 \\
   \end{matrix}
   $$
   

   produces:

$$ \begin{matrix} 1 & x & x^2 \\ 1 & y & y^2 \\ 1 & z & z^2 \\ \end{matrix} $$

MathJax will adjust the sizes of the rows and columns so that everything fits.

2. To add brackets, either use \left…\right as in section 6 of the tutorial, or replace matrix with pmatrix $\begin{pmatrix}1&2\\3&4\\ \end{pmatrix}$, bmatrix $\begin{bmatrix}1&2\\3&4\\ \end{bmatrix}$, Bmatrix $\begin{Bmatrix}1&2\\3&4\\ \end{Bmatrix}$, vmatrix $\begin{vmatrix}1&2\\3&4\\ \end{vmatrix}$, Vmatrix $\begin{Vmatrix}1&2\\3&4\\ \end{Vmatrix}$.

3. Use \cdots $\cdots$ \ddots $\ddots$ \vdots $\vdots$ when you want to omit some of the entries:

   $$\begin{pmatrix} 1 & a_1 & a_1^2 & \cdots & a_1^n \\ 1 & a_2 & a_2^2 & \cdots & a_2^n \\ \vdots & \vdots& \vdots & \ddots & \vdots \\ 1 & a_m & a_m^2 & \cdots & a_m^n \end{pmatrix}$$

4. For horizontally "augmented" matrices, put parentheses or brackets around a suitably-formatted table; see arrays ^[1] below for details. Here is an example:

$$ \left[\begin{array}{cc|c} 1&2&3\\ 4&5&6 \end{array}\right] $$

is produced by:

    $$ \left[
\begin{array}{cc|c}
  1&2&3\\
  4&5&6
\end{array}
\right] $$

The cc|c is the crucial part here; it says that there are three centered columns with a vertical bar between the second and third.

5. For vertically "augmented" matrices, use \hline. For example

$$ \begin{pmatrix} a & b \\ c & d\\ \hline 1 & 0\\ 0 & 1 \end{pmatrix} $$ is produced by

$$
  \begin{pmatrix}
    a & b\\
    c & d\\
  \hline
    1 & 0\\
    0 & 1
  \end{pmatrix}
$$

6. For small inline matrices use \bigl(\begin{smallmatrix} ... \end{smallmatrix}\bigr), e.g. $\bigl( \begin{smallmatrix} a & b \\ c & d \end{smallmatrix} \bigr)$ is produced by:

     $\bigl( \begin{smallmatrix} a & b \\ c & d \end{smallmatrix} \bigr)$
   

Symbols

In general, you have to search in long tables about a specific symbol you're looking for, things like $\Psi$, $\delta$, $\zeta$, $\ge$, $\subseteq$ ... And it turns out that this operation can be frustrating and time consuming, which can cause the buddy to abandon writing the complete $\LaTeX$ sentence in his answer, or in some cases, the complete answer itself.

That's why the tool that I will present you in this post was conceived. Basically, it is a $\LaTeX$ handwritten symbol recognition. Example in image:

Here is the website: Detexify² ^[1] No more frustration.

Aligned equations

Often people want a series of equations where the equals signs are aligned. To get this, use \begin{align}…\end{align}. Each line should end with \\, and should contain an ampersand at the point to align at, typically immediately before the equals sign.

For example,

\begin{align} \sqrt{37} & = \sqrt{\frac{73^2-1}{12^2}} \\ & = \sqrt{\frac{73^2}{12^2}\cdot\frac{73^2-1}{73^2}} \\ & = \sqrt{\frac{73^2}{12^2}}\sqrt{\frac{73^2-1}{73^2}} \\ & = \frac{73}{12}\sqrt{1 - \frac{1}{73^2}} \\ & \approx \frac{73}{12}\left(1 - \frac{1}{2\cdot73^2}\right) \end{align}

is produced by

\begin{align}
\sqrt{37} & = \sqrt{\frac{73^2-1}{12^2}} \\
 & = \sqrt{\frac{73^2}{12^2}\cdot\frac{73^2-1}{73^2}} \\ 
 & = \sqrt{\frac{73^2}{12^2}}\sqrt{\frac{73^2-1}{73^2}} \\
 & = \frac{73}{12}\sqrt{1 - \frac{1}{73^2}} \\ 
 & \approx \frac{73}{12}\left(1 - \frac{1}{2\cdot73^2}\right)
\end{align}

The usual $$ marks that delimit the display may be omitted here.

Definitions by cases (piecewise functions)

Warning: If you make certain kinds of errors while entering code using this environment, you can easily screw-up live update, and your only recourse is to abandon your edit and refresh the page. Clearing out the code and re-entering it will not fix things - you will have to refresh the page. If you are learning how to use this feature it is recommended that you cut-and-paste a working example from here, and modify it bit-by-bit to the text you want.

Use \begin{cases}…\end{cases}. End each case with a \\, and use & before parts that should be aligned.

For example, you get this:

$$f(n) = \begin{cases} n/2, & \text{if $n$ is even} \\ 3n+1, & \text{if $n$ is odd} \end{cases}$$

by writing this:

  f(n) =
\begin{cases}
n/2,  & \text{if $n$ is even} \\
3n+1, & \text{if $n$ is odd}
\end{cases}

The brace can be moved to the right: $$ \left. \begin{array}{l} \text{if $n$ is even:}&n/2\\ \text{if $n$ is odd:}&3n+1 \end{array} \right\} =f(n) $$ by writing this:

\left.
\begin{array}{l}
\text{if $n$ is even:}&n/2\\
\text{if $n$ is odd:}&3n+1
\end{array}
\right\}
=f(n)

To get a larger vertical space between cases we can use \\[2ex] instead of \\. For example, you get this:

$$f(n) = \begin{cases} \frac{n}{2}, & \text{if $n$ is even} \\[2ex] 3n+1, & \text{if $n$ is odd} \end{cases}$$

by writing this:

f(n) =
\begin{cases}
\frac{n}{2},  & \text{if $n$ is even} \\[2ex]
3n+1, & \text{if $n$ is odd}
\end{cases}

(An ‘ex’ is a length equal to the height of the letter x; 2ex here means the space should be two exes high.)

Arrays

It is often easier to read tables formatted in MathJax rather than plain text or a fixed width font. Arrays and tables are created with the array environment. Just after \begin{array} the format of each column should be listed, use c for a center aligned column, r for right aligned, l for left aligned and a | for a vertical line. Just as with matrices, cells are separated with & and rows are broken using \\. A horizontal line spanning the array can be placed before the current line with \hline.

For example, $$\begin{array}{c|lcr} n & \text{Left} & \text{Center} & \text{Right} \\ \hline 1 & 0.24 & 1 & 125 \\ 2 & -1 & 189 & -8 \\ 3 & -20 & 2000 & 1+10i \end{array} $$

$$
\begin{array}{c|lcr}
n & \text{Left} & \text{Center} & \text{Right} \\
\hline
1 & 0.24 & 1 & 125 \\
2 & -1 & 189 & -8 \\
3 & -20 & 2000 & 1+10i
\end{array}
$$

Arrays can be nested to make an array of tables.

For example, $$ % outer vertical array of arrays \begin{array}{c} % inner horizontal array of arrays \begin{array}{cc} % inner array of minimum values \begin{array}{c|cccc} \text{min} & 0 & 1 & 2 & 3\\ \hline 0 & 0 & 0 & 0 & 0\\ 1 & 0 & 1 & 1 & 1\\ 2 & 0 & 1 & 2 & 2\\ 3 & 0 & 1 & 2 & 3 \end{array} & % inner array of maximum values \begin{array}{c|cccc} \text{max}&0&1&2&3\\ \hline 0 & 0 & 1 & 2 & 3\\ 1 & 1 & 1 & 2 & 3\\ 2 & 2 & 2 & 2 & 3\\ 3 & 3 & 3 & 3 & 3 \end{array} \end{array} \\ % inner array of delta values \begin{array}{c|cccc} \Delta&0&1&2&3\\ \hline 0 & 0 & 1 & 2 & 3\\ 1 & 1 & 0 & 1 & 2\\ 2 & 2 & 1 & 0 & 1\\ 3 & 3 & 2 & 1 & 0 \end{array} \end{array} $$

As the source for the preceding array is long, please right-click on one of the tables and choose $\mathsf{Show\ Math\ As\ }\blacktriangleright\mathsf{\ TeX\ Commands}$.

Fussy spacing issues

These are issues that won't affect the correctness of formulas, but might make them look significantly better or worse. Beginners should feel free to ignore this advice; someone else will correct it for them, or more likely nobody will care.

Don't use \frac in exponents or limits of integrals; it looks bad and can be confusing, which is why it is rarely done in professional mathematical typesetting. Write the fraction horizontally, with a slash:

$$\begin{array}{cc} \mathrm{Bad} & \mathrm{Better} \\ \hline \\ e^{i\frac{\pi}2} \quad e^{\frac{i\pi}2}& e^{i\pi/2} \\ \int_{-\frac\pi2}^\frac\pi2 \sin x\,dx & \int_{-\pi/2}^{\pi/2}\sin x\,dx \\ \end{array}$$

The | symbol has the wrong spacing when it is used as a divider, for example in set comprehensions. Use \mid instead:

$$\begin{array}{cc} \mathrm{Bad} & \mathrm{Better} \\ \hline \\ \{x|x^2\in\Bbb Z\} & \{x\mid x^2\in\Bbb Z\} \\ \end{array}$$

When using stretchable delimiters (i.e. with \left and \right), it may be preferable to use \,\middle|\,. This produces a stretchable vertical bar with a little bit of space around it. Another alternative is to use a colon instead.

$$\begin{array}{cc} \mathrm{Bad} & \mathrm{Better} \\ \hline \\ \left\{\dfrac{m}{n} \mid m,n\in\Bbb Z\right\} & \left\{\dfrac{m}{n} \,\middle|\, m,n\in\Bbb Z\right\} \\ \end{array}$$

For double and triple integrals, don't use \int\int or \int\int\int. Instead use the special forms \iint and \iiint: $$\begin{array}{cc} \mathrm{Bad} & \mathrm{Better} \\ \hline \\ \int\int_S f(x)\,dy\,dx & \iint_S f(x)\,dy\,dx \\ \int\int\int_V f(x)\,dz\,dy\,dx & \iiint_V f(x)\,dz\,dy\,dx \end{array}$$

Use \, to insert a thin space before differentials; without this $\TeX$ will mash them together:

$$\begin{array}{cc} \mathrm{Bad} & \mathrm{Better} \\ \hline \\ \iiint_V f(x)dz dy dx & \iiint_V f(x)\,dz\,dy\,dx \end{array}$$

When using a function (e.g. $f$, $\sin$, etc) followed by arguments with larger parentheses, insert negative space before the parentheses using \!:

$$\begin{array}{cc} \mathrm{Bad} & \mathrm{Better} \\ \hline \\ f\left( \dfrac{1}{x} \right) & f\!\left(\dfrac{1}{x}\right) \end{array}$$

When using absolute value, use \lvert ... \rvert instead of a pair of pipes |...|.

$$\begin{array}{cc} \mathrm{Bad} & \mathrm{Better} \\ \hline \\ |\sin x| & \lvert\sin x\rvert \end{array}$$

Crossing things out

Use \require{cancel} in the first formula in your post that requires cancelling; you need it only once per page. Then use:

$$\require{cancel}\begin{array}{rl} \verb|y+\cancel{x}| & y+\cancel{x}\\ \verb|\cancel{y+x}| & \cancel{y+x}\\ \verb|y+\bcancel{x}| & y+\bcancel{x}\\ \verb|y+\xcancel{x}| & y+\xcancel{x}\\ \verb|y+\cancelto{0}{x}| & y+\cancelto{0}{x}\\ \verb+\frac{1\cancel9}{\cancel95} = \frac15+& \frac{1\cancel9}{\cancel95} = \frac15 \\ \end{array} $$

Use \require{enclose} for the following:

$$\require{enclose}\begin{array}{rl} \verb|\enclose{horizontalstrike}{x+y}| & \enclose{horizontalstrike}{x+y}\\ \verb|\enclose{verticalstrike}{\frac xy}| & \enclose{verticalstrike}{\frac xy}\\ \verb|\enclose{updiagonalstrike}{x+y}| & \enclose{updiagonalstrike}{x+y}\\ \verb|\enclose{downdiagonalstrike}{x+y}| & \enclose{downdiagonalstrike}{x+y}\\ \verb|\enclose{horizontalstrike,updiagonalstrike}{x+y}| & \enclose{horizontalstrike,updiagonalstrike}{x+y}\\ \end{array} $$

\enclose can also produce enclosing boxes, circles, and other notations; see MathML menclose documentation ^[1] for a complete list.

It is worth noting that MathJax should not be used for formatting non-mathematical text. The preferred way for striking out text is to use the HTML strikethrough tag, <s>[text to be striken]</s>, which renders as [text to be striken].

Additional decorations

$\def\demo#1#2{#1{#2}\ #1{#2#2}\ #1{#2#2#2}}$

\overline: $\demo\overline A$

\underline: $\demo\underline B$

\widetilde: $\demo\widetilde C$

\widehat: $\demo\widehat D$

\fbox: $\demo\fbox {$E$}$

\underleftarrow: $\demo\underleftarrow{F}\qquad$ variant: \xleftarrow{}: $\xleftarrow{abc}$

\underrightarrow: $\demo\underrightarrow{G}\qquad$ variant: \xrightarrow{}: $\xrightarrow{abc}$

\underleftrightarrow: $\demo\underleftrightarrow{H}$

\overrightarrow $\demo\overrightarrow{AB}$

\overbrace: $\overbrace{(n - 2) + (n - 1) + (n + 0) + (n + 1) + (n + 2)}$

\underbrace: $\underbrace{(n - 2) + (n - 1) + (n + 0) + (n + 1) + (n + 2)}$

\underbrace: underbraces can be nested, like this: $\underbrace{(n - 2) + \underbrace{(n - 1) + \underbrace{(n + 0)} + (n + 1)} + (n + 2)}$

\overbrace and \underbrace accept a superscript or a subscript, respectively, to annotate the brace. For example, \underbrace{a\cdot a\cdots a}_{b\text{ times}} is $$\underbrace{a\cdot a\cdots a}_{b\text{ times}}$$

Note: \varliminf: $\varliminf$ and \varlimsup:$\varlimsup$ have special symbol of their own.

Single character accents

\check: $\check{I}$

\acute: $\acute{J}$

\grave: $\grave{K}$

\vec: $\vec u\ \vec{AB}$ (c.f. \overrightarrow above)

\bar: $\bar z$

\hat: $\hat x$

\tilde: $\tilde x$

\dot \ddot \dddot: $\dot x,\ddot x,\dddot x$

\mathring: $\mathring A$

General stacking

If you cannot find your symbol remember that you can stack various symbols using

\overset{above}{level}: $\overset{@}{ABC}\ \overset{x^2}{\longmapsto}\ \overset{\bullet\circ\circ\bullet}{T}$

\underset{below}{level}: $\underset{@}{ABC}\ \underset{x^2}{\longmapsto}\ \underset{\bullet\circ\circ\bullet}{T}$

You can use these together too. You can type $X \overset{a}{\underset{b}{\to}} Y$ with X\overset{a}{\underset{b}{\to}}Y.

Arc over points

\overset{ \huge\frown}{PQ}: $\overset{ \huge\frown}{PQ}$ denotes the arc over points $P$ and $Q$ (As per comment of @Calvin Khor to @Paul Sinclair's question)

Commutative diagrams

(For more examples, see this meta question ^[1].)

AMScd diagrams must start with a "require":

$\require{AMScd}$
\begin{CD}
A @>a>> B\\
@V b V V= @VV c V\\
C @>>d> D
\end{CD}

to get this diagram: $\require{AMScd}$ \begin{CD} A @>a>> B\\ @V b V V= @VV c V\\ C @>>d> D \end{CD}

@>>> is used for arrow right

@<<< is used for arrow left

@VVV is used for arrow down

@AAA is used for arrow up

@= is used for horizontal double line

@| is used for vertical double line

@. is used for no arrow

Another example:

    \begin{CD}
    A @>>> B @>{\text{very long label}}>> C \\
    @. @AAA @| \\
    D @= E @<<< F
\end{CD}

\begin{CD} A @>>> B @>{\text{very long label}}>> C \\ @. @AAA @| \\ D @= E @<<< F \end{CD}

Long labels increase the length of the arrow and in this version also automatically increase corresponding arrows.

$\require{AMScd}$
\begin{CD}
  RCOHR'SO_3Na @>{\text{Hydrolysis,$\Delta, Dil.HCl$}}>> (RCOR')+NaCl+SO_2+ H_2O 
\end{CD}

$\require{AMScd}$ \begin{CD} \text{RCOHR'SO$_3$Na} @>{\text{Hydrolysis, $\Delta,$ Dil. HCl}}>> \text{(RCOR')+NaCl+SO$_2$+ H$_2$O} \end{CD}

System of equations

• Use \begin{array}…\end{array} and \left\{…\right.. For example, you get this:

$$ \left\{ \begin{array}{c} a_1x+b_1y+c_1z=d_1 \\ a_2x+b_2y+c_2z=d_2 \\ a_3x+b_3y+c_3z=d_3 \end{array} \right. $$

by writing this:

$$
\left\{ 
\begin{array}{c}
a_1x+b_1y+c_1z=d_1 \\ 
a_2x+b_2y+c_2z=d_2 \\ 
a_3x+b_3y+c_3z=d_3
\end{array}
\right. 
$$

• Alternatively we can use \begin{cases}…\end{cases}. The same system

$$ \begin{cases} a_1x+b_1y+c_1z=d_1 \\ a_2x+b_2y+c_2z=d_2 \\ a_3x+b_3y+c_3z=d_3 \end{cases} $$

is produced by the following code

$$\begin{cases}
a_1x+b_1y+c_1z=d_1 \\ 
a_2x+b_2y+c_2z=d_2 \\ 
a_3x+b_3y+c_3z=d_3
\end{cases}
$$

• To align the = signs use \begin{aligned}...\end{aligned} and \left\{…\right. (see asmeurer's comment) $$\left\{\begin{aligned} a_1x+b_1y+c_1z&=d_1+e_1 \\ a_2x+b_2y&=d_2 \\ a_3x+b_3y+c_3z&=d_3 \end{aligned} \right. $$

whose code is

$$
\left\{
\begin{aligned} 
a_1x+b_1y+c_1z &=d_1+e_1 \\ 
a_2x+b_2y&=d_2 \\ 
a_3x+b_3y+c_3z &=d_3 
\end{aligned} 
\right. 
$$

• To align the = signs and the terms as in $$\left\{\begin{array}{ll}a_1x+b_1y+c_1z &=d_1+e_1 \\ a_2x+b_2y &=d_2 \\ a_3x+b_3y+c_3z &=d_3 \end{array} \right.$$

use array with l (for "align left"; there are also c and r) parameters

$$
\left\{
\begin{array}{ll}
a_1x+b_1y+c_1z &=d_1+e_1 \\ 
a_2x+b_2y &=d_2 \\ 
a_3x+b_3y+c_3z &=d_3 
\end{array} 
\right.
$$

• Vertical space between equations. As explained in Definition by cases ^[1] to get a larger vertical space between equations we can use \\[2ex] instead of \\. The system

$$\begin{cases} a_1x+b_1y+c_1z=\frac{p_1}{q_1} \\[2ex] a_2x+b_2y+c_2z=\frac{p_2}{q_2} \\[2ex] a_3x+b_3y+c_3z=\frac{p_3}{q_3} \end{cases} $$

is generated by the following code

$$\begin{cases} a_1x+b_1y+c_1z=d_1 \\[2ex] a_2x+b_2y+c_2z=d_2 \\[2ex] a_3x+b_3y+c_3z=d_3 \end{cases} $$

in comparison with

$$\begin{cases} a_1x+b_1y+c_1z=\frac{p_1}{q_1} \\ a_2x+b_2y+c_2z=\frac{p_2}{q_2} \\ a_3x+b_3y+c_3z=\frac{p_3}{q_3} \end{cases} $$

whose code is

$$\begin{cases} a_1x+b_1y+c_1z=\frac{p_1}{q_1} \\ a_2x+b_2y+c_2z=\frac{p_2}{q_2} \\ a_3x+b_3y+c_3z=\frac{p_3}{q_3} \end{cases} $$

• In response to elect's comment ^[2]. The following code

  $$ \left\{ \begin{array}{l} 0 = c_x-a_{x0}-d_{x0}\dfrac{(c_x-a_{x0})\cdot d_{x0}}{\|d_{x0}\|^2} + c_x-a_{x1}-d_{x1}\dfrac{(c_x-a_{x1})\cdot d_{x1}}{\|d_{x1}\|^2} \\[2ex] 0 = c_y-a_{y0}-d_{y0}\dfrac{(c_y-a_{y0})\cdot d_{y0}}{\|d_{y0}\|^2} + c_y-a_{y1}-d_{y1}\dfrac{(c_y-a_{y1})\cdot d_{y1}}{\|d_{y1}\|^2} \end{array} \right. $$

produces

$$ \left\{ \begin{array}{l} 0 = c_x-a_{x0}-d_{x0}\dfrac{(c_x-a_{x0})\cdot d_{x0}}{\|d_{x0}\|^2} + c_x-a_{x1}-d_{x1}\dfrac{(c_x-a_{x1})\cdot d_{x1}}{\|d_{x1}\|^2} \\[2ex] 0 = c_y-a_{y0}-d_{y0}\dfrac{(c_y-a_{y0})\cdot d_{y0}}{\|d_{y0}\|^2} + c_y-a_{y1}-d_{y1}\dfrac{(c_y-a_{y1})\cdot d_{y1}}{\|d_{y1}\|^2} \end{array} \right. $$

Colors

Named colors are browser-dependent; if a browser doesn't know a particular color name, it may render the text as black. The following colors are standard in HTML4 and CSS2 and should be interpreted the same by most browsers: $$\begin{array}{|rc|} \hline \verb+\color{black}{text}+ & \color{black}{text} \\ \verb+\color{gray}{text}+ & \color{gray}{text} \\ \verb+\color{silver}{text}+ & \color{silver}{text} \\ \verb+\color{white}{text}+ & \color{white}{text} \\ \hline \verb+\color{maroon}{text}+ & \color{maroon}{text} \\ \verb+\color{red}{text}+ & \color{red}{text} \\ \verb+\color{yellow}{text}+ & \color{yellow}{text} \\ \verb+\color{lime}{text}+ & \color{lime}{text} \\ \verb+\color{olive}{text}+ & \color{olive}{text} \\ \verb+\color{green}{text}+ & \color{green}{text} \\ \verb+\color{teal}{text}+ & \color{teal}{text} \\ \verb+\color{aqua}{text}+ & \color{aqua}{text} \\ \verb+\color{blue}{text}+ & \color{blue}{text} \\ \verb+\color{navy}{text}+ & \color{navy}{text} \\ \verb+\color{purple}{text}+ & \color{purple}{text} \\ \verb+\color{fuchsia}{text}+ & \color{magenta}{text} \\ \hline \end{array}$$

HTML5 and CSS 3 ^[1] define an additional 124 color names that will be supported on many browsers ^[2].

Math Stack Exchange's default style uses a light-colored page background, so avoid using light colors for text. Stick to darker colors like maroon, green, blue, and purple, and remember also that 7–10% of men are color-blind and have difficulty distinguishing red and green. (Some people have difficulty distinguishing other colors too, so don't rely on colors saying "the blue part" over and over again.)

The color may also have the form #rgb where $r, g, b$ are in the range or 0–9, a–f and represent the intensity of red, green, and blue on a scale of $0–15$, with a=10, b=11, … f=15. For example:

$$\begin{array}{|rrrrrrrr|}\hline \verb+#000+ & \color{#000}{text} & & & \verb+#00F+ & \color{#00F}{text} & & \\ & & \verb+#0F0+ & \color{#0F0}{text} & & & \verb+#0FF+ & \color{#0FF}{text}\\ \verb+#F00+ & \color{#F00}{text} & & & \verb+#F0F+ & \color{#F0F}{text} & & \\ & & \verb+#FF0+ & \color{#FF0}{text} & & & \verb+#FFF+ & \color{#FFF}{text}\\ \hline \end{array} $$

$$\begin{array}{|rrrrrrrr|} \hline \verb+#000+ & \color{#000}{text} & \verb+#005+ & \color{#005}{text} & \verb+#00A+ & \color{#00A}{text} & \verb+#00F+ & \color{#00F}{text} \\ \verb+#500+ & \color{#500}{text} & \verb+#505+ & \color{#505}{text} & \verb+#50A+ & \color{#50A}{text} & \verb+#50F+ & \color{#50F}{text} \\ \verb+#A00+ & \color{#A00}{text} & \verb+#A05+ & \color{#A05}{text} & \verb+#A0A+ & \color{#A0A}{text} & \verb+#A0F+ & \color{#A0F}{text} \\ \verb+#F00+ & \color{#F00}{text} & \verb+#F05+ & \color{#F05}{text} & \verb+#F0A+ & \color{#F0A}{text} & \verb+#F0F+ & \color{#F0F}{text} \\ \hline \verb+#080+ & \color{#080}{text} & \verb+#085+ & \color{#085}{text} & \verb+#08A+ & \color{#08A}{text} & \verb+#08F+ & \color{#08F}{text} \\ \verb+#580+ & \color{#580}{text} & \verb+#585+ & \color{#585}{text} & \verb+#58A+ & \color{#58A}{text} & \verb+#58F+ & \color{#58F}{text} \\ \verb+#A80+ & \color{#A80}{text} & \verb+#A85+ & \color{#A85}{text} & \verb+#A8A+ & \color{#A8A}{text} & \verb+#A8F+ & \color{#A8F}{text} \\ \verb+#F80+ & \color{#F80}{text} & \verb+#F85+ & \color{#F85}{text} & \verb+#F8A+ & \color{#F8A}{text} & \verb+#F8F+ & \color{#F8F}{text} \\ \hline \verb+#0F0+ & \color{#0F0}{text} & \verb+#0F5+ & \color{#0F5}{text} & \verb+#0FA+ & \color{#0FA}{text} & \verb+#0FF+ & \color{#0FF}{text} \\ \verb+#5F0+ & \color{#5F0}{text} & \verb+#5F5+ & \color{#5F5}{text} & \verb+#5FA+ & \color{#5FA}{text} & \verb+#5FF+ & \color{#5FF}{text} \\ \verb+#AF0+ & \color{#AF0}{text} & \verb+#AF5+ & \color{#AF5}{text} & \verb+#AFA+ & \color{#AFA}{text} & \verb+#AFF+ & \color{#AFF}{text} \\ \verb+#FF0+ & \color{#FF0}{text} & \verb+#FF5+ & \color{#FF5}{text} & \verb+#FFA+ & \color{#FFA}{text} & \verb+#FFF+ & \color{#FFF}{text} \\ \hline \end{array}$$

You can have a look here for quick reference on colors in HTML ^[3].

Tags & References

For longer calculations (or referring to other post's results) it is convenient to use the tagging/labelling/referencing system. To tag an equation use \tag{yourtag}, and if you want to refer to that tag later on, add \label{somelabel} right after the \tag. It is not necessary that yourtag and somelabel are the same, but it usually is more convenient to do so:

$$ a := x^2-y^3 \tag{*}\label{*} $$

$$ a := x^2-y^3 \tag{*}\label{*} $$

In order to refer to an equation, just use \eqref{somelabel}

$$ a+y^3 \stackrel{\eqref{*}}= x^2 $$

$$ a+y^3 \stackrel{\eqref{*}}= x^2 $$

or \ref{somelabel}

Equations are usually referred to as $\eqref{*}$, but you can also use $\ref{*}$.

Equations are usually referred to as $\eqref{*}$, but you can also use $\ref{*}$.

As you can see, references are even turned into hyperlinks, which you can use externally as well, e.g. like this ^[1]. Note that you can also reference labels in other posts as long as they appear on the same site, which is especially useful when referring to a question with multiple equations, or when commenting on a post.

Due to a bug blocks containing a \label will break in preview ^[2], as a workaround you can put $\def\label#1{}$ in your post while editing and remove that on submission ^[3] - unfortunately this means you won't spot misspelled references before submitting... Just don't forget to remove that \def again

Continued fractions

To make a continued fraction, use \cfrac, which works just like \frac but typesets the results differently:

$$ x = a_0 + \cfrac{1^2}{a_1 + \cfrac{2^2}{a_2 + \cfrac{3^2}{a_3 + \cfrac{4^4}{a_4 + \cdots}}}}$$

Don't use regular \frac or \over, or it will look awful:

$$ x = a_0 + \frac{1^2}{a_1 + \frac{2^2}{a_2 + \frac{3^2}{a_3 + \frac{4^4}{a_4 + \cdots}}}}$$

You can of course use \frac for the compact notation:

$$ x = a_0 + \frac{1^2}{a_1+} \frac{2^2}{a_2+} \frac{3^2}{a_3 +} \frac{4^4}{a_4 +} \cdots$$

Continued fractions are too big to put inline. Display them with $$…$$ or use a notation like $[a_0; a_1, a_2, a_3, \ldots]$.

Using \newcommand

I would like to remark that it is possible to define LaTeX commands as you do in your TeX files. I felt so happy when I first discovered it! It's enough to insert something like

$ \newcommand{\SES}[3]{ 0 \to #1 \to #2 \to #3 \to 0 } $

$ \newcommand{\SES}[3]{ 0 \to #1 \to #2 \to #3 \to 0 }$ at the top of your post (remember the dollars!). Then you can just use your commands as you are used to do: in my example typing $$ \SES{A}{B}{C} $$ will produce the following:

$$ \SES{A}{B}{C} $$

It's also possible to use plain \def:

\def\ses#1#2#3{0 \to #1 \to #2 \to #3 \to 0}

and then $\ses{A}{B}{C}$ will produce the same output.

\implies ($\implies$) is a marginally preferable ^[1] alternative to \Rightarrow ($\Rightarrow$) for implication.

There's also \iff $\iff$ and \impliedby $\impliedby$.

\to ($\to$) is preferable to \rightarrow or \longrightarrow for things like $f\colon A \to B$. The reverse is \gets ($\gets$).

Big braces

Use \left and \right to make braces - (round), [square] and {curly} - scale up to be the size of their arguments. Thus

$$
f\left(
   \left[ 
 \frac{
   1+\left\{x,y\right\}
 }{
   \left(
      \frac{x}{y}+\frac{y}{x}
   \right)
   \left(u+1\right)
 }+a
   \right]^{3/2}
\right)
$$

renders as $$ f\left(\left[ \frac{1+\left\{x,y\right\}}{\left(\frac{x}{y}+\frac{y}{x}\right)\left(u+1\right)}+a\right]^{3/2}\right). $$

Note that curly braces need to be escaped as \{ \}.

If you start a big brace with \left and then need to match that to a \right brace that's on a different line, use the forms \right. and \left. to make "shadow" braces. Thus,

$$
\begin{aligned}
a=&\left(1+2+3+  \cdots \right. \\
& \cdots+ \left. \infty-2+\infty-1+\infty\right)
\end{aligned}
$$

renders as $$ \begin{aligned} a=&\left(1+2+3+ \cdots \right. \\ & \cdots+ \left. \infty-2+\infty-1+\infty\right). \end{aligned} $$

There is also a \middle construct which is useful when one has a mid-expression brace which must also scale up:

$$
\left\langle  
  q
\middle\|
  \frac{\frac{x}{y}}{\frac{u}{v}}
\middle| 
   p 
\right\rangle
$$

renders as $$ \left\langle q\middle\|\frac{\frac{x}{y}}{\frac{u}{v}} \middle| p \right\rangle. $$

Note that constructs like \left\langle, \left| and \left\| are also possible.

Alternatively there also exists the \big hierarchy whose pairing is not mandatory, you can type \big(\frac 1x\big) $\big(\frac 1x\big)$

The advantage of left/right is that it dimensions automatically, but has the inconvenient of not producing consistent results depending of the vertical extension of its inner content, instead the big hierarchy has fixed size:

\Bigg(\bigg(\Big(\big((x)\big)\Big)\bigg)\Bigg) $\Bigg(\bigg(\Big(\big((x)\big)\Big)\bigg)\Bigg)$

Limits

To make a limit (like $\lim \limits_{x \to 1} \frac{x^2-1}{x-1}$), use this syntax:

First, start off with $\lim. This renders as $\lim$. The backslash is there to prevent things like $lim$, where the letters are slanted.

Second, add \limits_{x \to 1} inside. The code now looks like $\lim \limits_{x \to 1}$, and renders as $\lim \limits_{x \to 1}$. The \to inside makes the right arrow, rendered as $\to$. The _ makes the $x \to 1$ go underneath the $\lim$. Finally, the pair of curly braces { } makes sure that $x \to 1$ is treated as a whole object, and not two separate things.

Lastly, add the function you want to apply the limit to. To make the limit mentioned above, $\lim \limits_{x \to 1} \frac{x^2-1}{x-1}$, simply use $\lim\limits_{x \to 1} \frac{x^2-1}{x-1}$.

And that is how you make a limit using MathJax.

Arbitrary operators

If an operator is not available as a built-in command, use \operatorname{…}. So for things like $$\operatorname{arsinh}(x)$$ write \operatorname{arsinh}(x) since \arsinh(x) will give an error and arsinh(x) has wrong font and spacing: $arsinh(x)$.

This was already mentioned in a comment ^[1] by Charles Staats ^[2]. You might consider this an addition to the FAQ section on \lim, \sin and so on.

For operators which need limits above and below the operator, use \operatorname*{…}, as in $$ \operatorname*{Res}_{z=1}\left(\frac1{z^2-z}\right)=1 $$

New operators may also be defined using the \DeclareMathOperator syntax: \DeclareMathOperator{newOperatorCommand}{newOperator}$\DeclareMathOperator{newOperatorCommand}{newOperator}$ defines a new operator. On the page where this code occurs, \newOperatorCommand will be rendered as $\newOperatorCommand$.

Highlighting equation

To highlight an equation, \bbox can be used. E.g,

$$ \bbox[yellow]
{
e^x=\lim_{n\to\infty} \left( 1+\frac{x}{n} \right)^n
\qquad (1)
}
$$

produces

$$ \bbox[yellow] { e^x=\lim_{n\to\infty} \left( 1+\frac{x}{n} \right)^n \qquad (1) } $$

By default, the bounding box is "tight", so it doesn't extend beyond the characters used in the formula. You can add a little space around the equation by adding a measurement after the color. E.g.,

$$ \bbox[yellow,5px]
{
e^x=\lim_{n\to\infty} \left( 1+\frac{x}{n} \right)^n
\qquad (1)
}
$$

produces

$$ \bbox[yellow,5px] { e^x=\lim_{n\to\infty} \left( 1+\frac{x}{n} \right)^n \qquad (1) } $$

To add a border, use

$$ \bbox[5px,border:2px solid red]
{
e^x=\lim_{n\to\infty} \left( 1+\frac{x}{n} \right)^n
\qquad (2) 
}
$$

produces

$$ \bbox[5px,border:2px solid red] { e^x=\lim_{n\to\infty} \left( 1+\frac{x}{n} \right)^n \qquad (2) } $$

You can do both border and background, as well:

$$ \bbox[yellow,5px,border:2px solid red]
{
e^x=\lim_{n\to\infty} \left( 1+\frac{x}{n} \right)^n
\qquad (1)
}
$$

produces

$$ \bbox[yellow,5px,border:2px solid red] { e^x=\lim_{n\to\infty} \left( 1+\frac{x}{n} \right)^n \qquad (1) } $$

Absolute values and norms

The absolute value of some expression can be denoted as \lvert x\rvert or, more generally, as \left\lvert … \right\rvert. It renders as $\lvert x\rvert$.

The norm of a vector (or similar) can be denoted as \lVert v\rVert or, more generally, as \left\lVert … \right\rVert. It renders as $\lVert v\rVert$. (You may also write \left\|…\right\| instead.)

In both cases, the rendering is better than what you'd get from |x| or ||v||, which render with bars that don't descend low enough and sub-optimal spacing. At least on some browsers, so here is a screenshot how it looks for me, using Firefox 31 on OS X:

And here is the same formula rendered by your browser:

$$|x|, ||v|| \quad\longrightarrow\quad \lvert x\rvert, \lVert v\rVert$$

It was typeset as

$$|x|, ||v|| \quad\longrightarrow\quad \lvert x\rvert, \lVert v\rVert$$

Giving reasons on each line of a sequence of equations

To produce this: \begin{align} v + w & = 0 &&\text{Given} \tag 1\\ -w & = -w + 0 && \text{additive identity} \tag 2\\ -w + 0 & = -w + (v + w) && \text{equations $(1)$ and $(2)$} \end{align}

write this:

\begin{align}
   v + w & = 0  &&\text{Given} \tag 1\\
   -w & = -w + 0 && \text{additive identity} \tag 2\\
   -w + 0 & = -w + (v + w) && \text{equations $(1)$ and $(2)$}
\end{align}

Pack of cards

If you are asking (or answering) a combinatorics question involving packs of cards you can make it look more elegant by using \spadesuit, \heartsuit, \diamondsuit, \clubsuit in math mode: $$\spadesuit\quad\heartsuit\quad\diamondsuit\quad\clubsuit$$ Or if you're really fussy:
\color{red}{\heartsuit} and \color{red}{\diamondsuit}
$$\color{red}{\heartsuit}\quad\color{red}{\diamondsuit}$$

You can also enter the standard Unicode characters (U+2660 BLACK SPADE SUIT etc.) literally, or copy them from here:

$$♠\quad♡\quad♢\quad♣\\ ♤\quad♥\quad♦\quad♧ $$

Left and Right Implication Arrows

Another way to display the arrows for right and left implication instead of using

$\Rightarrow$, $\Leftarrow$ and $\Leftrightarrow$

which produces $\Rightarrow$, $\Leftarrow$ and $\Leftrightarrow$ respectively, you can use

$\implies$ for $\implies$, $\impliedby$ for $\impliedby$ and $\iff$ for $\iff$

The latter of which produces longer arrows which may be more desirable to some.

Degree symbol

Standard Mathjax does not yet support a dedicated degree symbol, so here are some of the ways to try and emulate one :

$$ \begin{array} \\ \text{45^\text{o}} & \text{renders as} & 45^\text{o} \\ \text{45^o} & \text{renders as} & 45^o \\ \text{45^\circ} & \text{renders as} & 45^\circ \\ \text{45^{\large\circ}} & \text{renders as} & 45^{\large\circ}\\ \text{45\unicode{xB0}} & \text{renders as} & 45\unicode{xB0} & \text{Actual Unicode character}\\ \text{90°} & \text{renders as} & 90° & \text{Using keyboard entry of symbol} % % Use the following line as a template for additional entries % % \text{} & \text{renders as} & \\ \end{array} $$

The degree symbol for angles is not ^\circ. Although many people use this notation, the result looks quite different from the canonical degree symbol ^[1] shipped with the font, as seen above.

If your keyboard doesn't have a ° key, feel free to copy from this post here, or follow these suggestions ^[2].

Note that comments below indicate that on some configurations at least, ° renders inferior to ^\circ. And I recently had a post of mine edited ^[3] just for the sake of turning ° into ^\circ, indicating that someone felt rather strongly about this. So the suggestion above does seem somewhat controversial at the moment. I maintain that from a semantic point of view, ° is superior to ^\circ, and if the rendering suffers from this, then it's a bug in MathJax. After all, LaTeX offers a proper degree symbol in the tex companion fonts, indicating that someone there, too, decided that ^\circ is not perfect. But if things are broken now, I can't fault people from pragmatically sticking with the rendering they prefer. Personally I prefer semantics, also for the sake of screen readers.

Accessibility

Aside from appearance, one consideration in choosing which notation to use is how it will get parsed by screen readers. For example, ChromeVox ^[4] reads both 45^\circ and 45° as "forty-five degrees", while the other two are pronounced as "forty-five oh", which may be a reason to avoid them.

Usepackage

Commonly in Latex you can \usepackage{gensymb} to get the \degree symbol, however on Stack Exchange this is not an option. Note that even if you can do this it will typically affect the entire page, which may have side effects for other users. So don't rely on this approach.

Long division

$$
\require{enclose}
\begin{array}{r}
                13  \\[-3pt]
4 \enclose{longdiv}{52} \\[-3pt]
     \underline{4}\phantom{2} \\[-3pt]
                12  \\[-3pt]
     \underline{12}
\end{array}
$$

$$ \require{enclose} \begin{array}{r} 13 \\[-3pt] 4 \enclose{longdiv}{52} \\[-3pt] \underline{4}\phantom{2} \\[-3pt] 12 \\[-3pt] \underline{12} \end{array} $$

One important trick shown here is the use of \phantom{2} to make a blank space that is the same size and shape as the digit 2 just above it.

This is adapted from https://stackoverflow.com/a/22871404/3466415 (which uses slightly different but not less valid formatting).

Displaystyle and Textstyle

Many things like fractions, sums, limits, and integrals display differently when written inline versus in a displayed formula. You can switch styles back and forth with \displaystyle and \textstyle in order to achieve the desired appearance.

Here's an example switching back and forth in a displayed equation:

$$\sum_{n=1}^\infty \frac{1}{n^2} \to
      \textstyle \sum_{n=1}^\infty \frac{1}{n^2} \to
      \displaystyle \sum_{n=1}^\infty \frac{1}{n^2}$$

$$\sum_{n=1}^\infty \frac{1}{n^2} \to \textstyle \sum_{n=1}^\infty \frac{1}{n^2} \to \displaystyle \sum_{n=1}^\infty \frac{1}{n^2}$$

It is possible to switch style inline as well:

Compare $\displaystyle \lim_{t \to 0} \int_t^1 f(t)\, dt$
versus $\lim_{t \to 0} \int_t^1 f(t)\, dt$.

Compare $\displaystyle \lim_{t \to 0} \int_t^1 f(t)\, dt$ versus $\lim_{t \to 0} \int_t^1 f(t)\, dt$.

Do observe that the taller formulas gotten with \displaystyle distort the line spacing.

Filler text, more filler text and even more filler text, and an outrageous amount of filler text. It would not occur to me to use $\displaystyle \lim_{t \to 0} \int_t^1 f(x)\, dx$ here. As we see, a formula typeset in displaystyle makes it necessary to move the lines further apart. A ridiculous amount of filler text to make a point. Not pleasing to the eye at all.

In other words, there is also a reason TeX defaults to \textstyle when typesetting inline formulas.

Vertical Spacing

Some formulas such as $\overline a+\overline b=\overline {a\cdot b}$, $\sqrt{a}-\sqrt{b}$, do not look quite right when it comes to vertical spacing. Fortunately, there is more than one way to fix this. One can for instance employ the \mathstrut command as follows:

$\sqrt{\mathstrut a} - \sqrt{\mathstrut b}$

Which yields: $\sqrt{\mathstrut a} - \sqrt{\mathstrut b}$. Or using \vphantom (vertical phantom) command, which measures the height of its argument and places a math strut of that height into the formula.

$\sqrt{\vphantom{b} a} - \sqrt{b}$

Which renders as: $\sqrt{\vphantom{b} a} - \sqrt{b}$.

Another issue is with the spacing within lines in situations like this,

Based on the previous technique, we can simplify $\dfrac{1}{\sqrt{\vphantom{b} a} - \sqrt{b}}$, and we thus get the result of the previous limit. [this text is added to show alignment with the above smashed object]

These two lines are too far apart, but this is unnecessary since the second line is very short. We can solve this by using the \smash command, to get:

Based on the previous technique, we can simplify $\smash{\dfrac{1}{\sqrt{\vphantom{b} a} - \sqrt{b}}}$, and we thus get the result of the previous limit. [this text is added to show alignment with the above smashed object]

Beware - as above - the smashed text may overlap the next line if that line extends far enough to reach the smashed object, so this solution is not always feasible (it is esp. likely to occur in slim-width browsers, e.g. phones). Analogous overlapping may occur with any prior lines. Note that smash can be restricted to top or bottom with an argument: \smash[t]... or \smash[b]...

Equation numbering

Simple equation

To give an equation a number, use the \tag{}. To refer to it later, use \label{} to label this equation. When you want to refer to it, use \eqref{}. For example,

$$e=mc^2 \tag{1}\label{eq1}$$

Equation $\eqref{eq1}$ is one of the greatest equations in mankind's history. Equation $\eqref{eq1}$ is produced using the following code,

$$e=mc^2 \tag{1}\label{eq1}$$

To refer to it, use \eqref{eq1}.

Multi-line equation

Multi-line equation is actually just one equation rather than several equations. So the correct environment is aligned instead of align.

$$\begin{equation}\begin{aligned} a &= b + c \\ &= d + e + f + g \\ &= h + i \end{aligned}\end{equation}\tag{2}\label{eq2}$$

Equation $\eqref{eq2}$ is a multi-line equation. The code to produce equation $\eqref{eq2}$ is

$$\begin{equation}\begin{aligned}
a &= b + c \\
  &= d + e + f + g \\
  &= h + i
\end{aligned}\end{equation}\tag{2}\label{eq2}$$

Multiple aligned equations

For multiple aligned equations, we use the align environment.

$$\begin{align} a &= b + c \tag{3}\label{eq3} \\ x &= yz \tag{4}\label{eq4}\\ l &= m - n \tag{5}\label{eq5} \end{align}$$

Equation $\eqref{eq3}$, $\eqref{eq4}$ and $\eqref{eq5}$ are multiple equations aligned together. The code to produce these equations is,

$$\begin{align}
a &= b + c \tag{3}\label{eq3} \\
x &= yz \tag{4}\label{eq4}\\
l &= m - n \tag{5}\label{eq5}
\end{align}$$

Linear programming

Formulation

A theoretical LPP can be typeset as

\begin{array}{ll}
\text{maximize}  & c^T x \\
\text{subject to}& d^T x = \alpha \\
&0 \le x \le 1.
\end{array}

\begin{array}{ll} \text{maximize} & c^T x \\ \text{subject to}& d^T x = \alpha \\ &0 \le x \le 1. \end{array}

To input a numerical LPP, use alignat instead of align to get better alignment between signs, variables and coefficients.

\begin{alignat}{5}
  \max \quad        & z = &   x_1  & + & 12 x_2  &   &       &         && \\
  \mbox{s.t.} \quad &     & 13 x_1 & + & x_2     & + & 12x_3 & \geq 5  && \tag{constraint 1} \\
                    &     & x_1    &   &         & + & x_3   & \leq 16 && \tag{constraint 2} \\
                    &     & 15 x_1 & + & 201 x_2 &   &       & =    14 && \tag{constraint 3} \\
                    &     & \rlap{x_i \ge 0, i = 1, 2, 3}
\end{alignat}

\begin{alignat}{5} \max \quad & z = & x_1 & + & 12 x_2 & & & && \\ \mbox{s.t.} \quad & & 13 x_1 & + & x_2 & + & 12x_3 & \geq 5 && \tag{constraint 1} \\ & & x_1 & & & + & x_3 & \leq 16 && \tag{constraint 2} \\ & & 15 x_1 & + & 201 x_2 & & & = 14 && \tag{constraint 3} \\ & & \rlap{x_i \ge 0, i = 1, 2, 3} \end{alignat}

We treat $\max$, $z$, each variable, $\pm$ sign and RHS as one separate column, while leaving an extra empty column on the right. Then we count the number of separators &, add one into this number then divide it by two. (e.g. (9 + 1) ÷ 2 = 5)

\rlap is used so that the last row spans over one column.

Optional: \tag is used to label the constraints.

Change MATLAB/Octave matrices to $\rm\LaTeX$ code

To get fractions, execute format rat at the beginning.

Writing manually the $\rm\LaTeX$ code for a matrix with many rows and columns in Octave is tedious. The Octave function

strcat("\\begin{bmatrix}\n",strrep(strrep(mat2str(A)," "," & "), ...
";"," \\\\\n")(2:end-1),"\n\\end{bmatrix}\n")

converts

A = [1 2 2; 2 3 4; 4 4 2]
A =

   1   2   2
   2   3   4
   4   4   2

to

\begin{bmatrix}
1 & 2 & 2 \\
2 & 3 & 4 \\
4 & 4 & 2
\end{bmatrix}

so that pasting the generated code gives

$$ \begin{bmatrix} 1 & 2 & 2 \\ 2 & 3 & 4 \\ 4 & 4 & 2 \end{bmatrix}. $$

Simplex tableaux

Since the coefficient of the objective value variable $z$ never changes, my habit is to omit the $z$-column to save ink.

Normal simplex tableau

\begin{array}{rrrrrr|r}
               & x_1 & x_2 & s_1 & s_2 & s_3 &    \\ \hline
           s_1 &   0 &   1 &   1 &   0 &   0 &  8 \\
           s_2 &   1 &  -1 &   0 &   1 &   0 &  4 \\
           s_3 &   1 &   1 &   0 &   0 &   1 & 12 \\ \hline
               &  -1 &  -1 &   0 &   0 &   0 &  0
\end{array}

\begin{array}{rrrrrr|r} & x_1 & x_2 & s_1 & s_2 & s_3 & \\ \hline s_1 & 0 & 1 & 1 & 0 & 0 & 8 \\ s_2 & 1 & -1 & 0 & 1 & 0 & 4 \\ s_3 & 1 & 1 & 0 & 0 & 1 & 12 \\ \hline & -1 & -1 & 0 & 0 & 0 & 0 \end{array}

It can be stacked up to give an illustration of the entering of variables at different stages.

\begin{array}{rrrrrrr|rr}
      & x_1 & x_2 & s_1 & s_2 & s_3 &  w &    & \text{ratio} \\ \hline
  s_1 &   0 &   1 &   1 &   0 &   0 &  0 &  8 &            - \\
    w & 1^* &  -1 &   0 &  -1 &   0 &  1 &  4 &            4 \\
  s_3 &   1 &   1 &   0 &   0 &   1 &  0 & 12 &           12 \\ \hdashline
      &   1 &  -1 &   0 &  -1 &   0 &  0 &  4 &              \\ \hline
  s_1 &   0 &   1 &   1 &   0 &   0 &  0 &  8 &              \\
  x_1 &   1 &  -1 &   0 &  -1 &   0 &  1 &  4 &              \\
  s_3 &   0 &   2 &   0 &   2 &   1 & -1 &  8 &              \\ \hdashline
      &   0 &   0 &   0 &   0 &   0 & -1 &  0 &
\end{array}

\begin{array}{rrrrrrr|rr} & x_1 & x_2 & s_1 & s_2 & s_3 & w & & \text{ratio} \\ \hline s_1 & 0 & 1 & 1 & 0 & 0 & 0 & 8 & - \\ w & 1^* & -1 & 0 & -1 & 0 & 1 & 4 & 4 \\ s_3 & 1 & 1 & 0 & 0 & 1 & 0 & 12 & 12 \\ \hdashline & 1 & -1 & 0 & -1 & 0 & 0 & 4 & \\ \hline s_1 & 0 & 1 & 1 & 0 & 0 & 0 & 8 & \\ x_1 & 1 & -1 & 0 & -1 & 0 & 1 & 4 & \\ s_3 & 0 & 2 & 0 & 2 & 1 & -1 & 8 & \\ \hdashline & 0 & 0 & 0 & 0 & 0 & -1 & 0 & \end{array}

Dual simplex tableau

\begin{array}{rrrrrrrr|r}
             & x_1 & x_2 & x_3 & x_4 & x_5 & x_6 &  x_7 &        \\ \hline
         x_4 &   0 &  -3 &   7 &   1 &   0 &   0 &    2 & 2M  -4 \\
         x_5 &   0 &  -9 &   0 &   0 &   1 &   0 &   -1 & -M  -3 \\
         x_6 &   0 &   6 &  -1 &   0 &   0 &   1 & -4^* & -4M +8 \\
         x_1 &   1 &   0 &   1 &   0 &   0 &   0 &    1 &      M \\ \hline
             &   0 &   1 &   1 &   0 &   0 &   0 &    2 &     2M \\
\text{ratio} &     &     &   1 &     &     &     &  1/2 &
\end{array}

\begin{array}{rrrrrrrr|r} & x_1 & x_2 & x_3 & x_4 & x_5 & x_6 & x_7 & \\ \hline x_4 & 0 & -3 & 7 & 1 & 0 & 0 & 2 & 2M -4 \\ x_5 & 0 & -9 & 0 & 0 & 1 & 0 & -1 & -M -3 \\ x_6 & 0 & 6 & -1 & 0 & 0 & 1 & -4^* & -4M +8 \\ x_1 & 1 & 0 & 1 & 0 & 0 & 0 & 1 & M \\ \hline & 0 & 1 & 1 & 0 & 0 & 0 & 2 & 2M \\ \text{ratio} & & & 1 & & & & 1/2 & \end{array}

It can be stacked up to give a theoretical illustration of what happens in the upcoming steps.

\begin{array}{rrrrrrr|r} & x_1 & x_2 & x_3 & s_1 & s_2 & s_3 & \\ \hline s_1 & -2 & 0 & -2 & 1 & 0 & 0 & -60 \\ s_2 & -2 & -4^* & -5 & 0 & 1 & 0 & -70 \\ s_3 & 0 & -3 & -1 & 0 & 0 & 1 & -27 \\ \hdashline & 8 & 10 & 25 & 0 & 0 & 0 & 0 \\ \text{ratio} & -4 & -5/2 & -5 & & & & \\ \hline s_1 & -2^* & 0 & -2 & 1 & 0 & 0 & -60 \\ x_2 & 1/2 & 1 & 5/4 & 0 & -1/4 & 0 & 35/2 \\ s_3 & 3/2 & 0 & 11/4 & 0 & -3/4 & 1 & 51/2 \\ \hdashline & 3 & 0 & 25/2 & 0 & 5/2 & 0 & -175 \\ \text{ratio} & -3/2 & & 25/4 & & & & \\ \hline x_1 & 1 & 0 & 1 & -1/2 & 0 & 0 & 30 \\ x_2 & 0 & 1 & 3/4 & 1/4 & -1/4 & 0 & 5/2 \\ s_3 & 0 & 0 & 5/4 & 3/4 & -3/4^* & 1 & -39/2 \\ \hdashline & 0 & 0 & 19/2 & 3/2 & 5/2 & 0 & -265 \\ \text{ratio} & & & & & \dots & & \\ \hline x_1 & 1 & 0 & 1 & -1/2 & 0 & 0 & 30 \\ x_2 & 0 & 1 & 1/3 & 0 & 0 & -1/3 & 9 \\ s_2 & 0 & 0 & -5/3 & -1 & 1 & -4/3 & 26 \\ \hdashline & 0 & 0 & 41/3 & 4 & 0 & 10/3 & -330 \end{array}

Duality

A picture is worth a thousand words ^[1].

$$ \require{extpfeil} % produce extensible horizontal arrows \begin{array}{ccc} % arrange LPPs % first row % first LPP \begin{array}{ll} \max & z = c^T x \\ \text{s.t.} & A x \le b \\ & x \ge 0 \end{array} & \xtofrom{\text{duality}} & % second LPP \begin{array}{ll} \min & v = b^T y \\ \text{s.t.} & A^T y \ge c \\ & y \ge 0 \end{array} \\ ({\cal PC}) & & ({\cal DC}) \\ \text{add } {\Large \downharpoonleft} \text{slack var} & & \text{minus } {\Large \downharpoonright} \text{surplus var}\\ % Change to your favorite arrow style % % second row % third LPP \begin{array}{ll} \max & z = c^T x \\ \text{s.t.} & A x + s = b \\ & x,s \ge 0 \end{array} & \xtofrom[\text{some steps skipped}]{\text{duality}} & % fourth LPP \begin{array}{ll} \min & v = b^T y \\ \text{s.t.} & A^T y - t = c \\ & y,t \ge 0 \end{array} \\ ({\cal PS}) & & ({\cal DS}) % \end{array} $$

Units

While $\LaTeX$ has packages that format units, MathJax does not. For visual consistency, one should format units within the same string of MathJax code as the value to which it corresponds, separating the value and unit with \ (space-backslash-space) since the BIPM ^[1] recommends a small space between the value and units. In addition, follow the below conventions for formatting values and units:

Decimal Separator & Digit Separation

Following the conventions of the English-speaking world, a period . should be used to separate the decimal part of a number from the integral part, not a comma , as is common in some languages. This is because commas are already reserved for separating mathematical notation such as arguments of multivariate functions, elements of a set, and the coordinates of ordered tuples.

No punctuation should be used to separate multiples of three digits on either side of the decimal separator; instead, a small space rendered by \, should be used on both sides of the decimal marker when the string of digits consists of more than four or five digits. For example,

• 4321.1234 $4321.1234$
• 54\,321.123\,45 $54\,321.123\,45$
• 0.56789 $0.56789$
• 0.567\,89 $0.567\,89$

If you use a decimal separator, you should include a digit on both sides of the separator, even if the digit is simply $0$.

Powers of $10$

It is preferable to write scientific or engineering notation like this: 4.15\times10^{n} $4.15 \times10^{n}$. The spacing around \times $\times$ is taken care of on its own, so there is no need to insert the spacing manually.

Nevertheless, if necessary, use an upright variant of the letter ‘E’ or ‘e’ to indicate order of magnitude, such as

• \mathrm{E}\,6 $\mathrm{E}\,6$
• \scriptsize{\mathrm{E}}\,\normalsize{6} $\scriptsize{\mathrm{E}}\,\normalsize{6}$
• \mathrm{e}\,6 $\mathrm{e}\,6$

A small space on either side is perfectly fine and recommended.

Single Units

The symbol of any unit—especially SI units—should follow the form \mathrm{u}. (I have this command saved under the keyboard shortcut usin on my devices.) For example,

• \mathrm{m} $\mathrm{m}$
• \mathrm{kg} $\mathrm{kg}$
• \mathrm{ft.} $\mathrm{ft.}$

Do not use a period with symbolic units; do use a period with abbreviated units.

Units with a Dot Multiplier

Multiplied units conjoined by a dot should follow the form \mathrm{u}\!\cdot\!\mathrm{v} $\mathrm{u}\!\cdot\!\mathrm{v}$. (I have this sequence of commands saved under the keyboard shortcut umul on my devices.) Because of how \cdot is designed (i.e., to separate numbers), the small negative space \! on either side maintains uniform spacing throughout the whole compound unit. For example,

• \mathrm{N}\!\cdot\!\mathrm{m} $\mathrm{N}\!\cdot\!\mathrm{m}$
• \mathrm{s}\!\cdot\!\mathrm{A} $\mathrm{s}\!\cdot\!\mathrm{A}$

Do not use \times $\times$ as a separator.

Units with a Solidus Separator

Divided units conjoined by a solidus should follow the form \left.\mathrm{u}\middle/\mathrm{v}\right. $\left.\mathrm{u}\middle/\mathrm{v}\right.$. (I have this sequence of commands saved under the keyboard shortcut udiv on my devices.) The extra markdown is to ensure that solidus stretches the entire height of the unit, especially when exponents are involved. For example,

• \left.\mathrm{J}\middle/\mathrm{s}\right. $\left.\mathrm{J}\middle/\mathrm{s}\right.$
• \left.\mathrm{m}\middle/\mathrm{s}^2\right. $\left.\mathrm{m}\middle/\mathrm{s}^2\right.$

You may include small negative spaces \! on either side of the solidus if you please.

Exponents

Exponents can be rendered with the standard MathJax markdown. The carat and number should immediately follow the closing brace of the mathrm{} argument. For example,

• \mathrm{m}^2 $\mathrm{m}^2$
• \left.\mathrm{m}\middle/\mathrm{s}^2\right. $\left.\mathrm{m}\middle/\mathrm{s}^2\right.$

Parentheses

Parentheses can also be rendered with standard MathJax markdown using \left( and \right) outside the argument of \mathrm. For example,

• \left.\mathrm{kg}\!\cdot\!\mathrm{m}^2\middle/\left(\mathrm{C}\!\cdot\!\mathrm{s}\right)\right. $\left.\mathrm{kg}\!\cdot\!\mathrm{m}^2\middle/\left(\mathrm{C}\!\cdot\!\mathrm{s}\right)\right.$

Exponents in Place of Separators

If you prefer to use no separators and only powers, separator each single \mathrm{} with a small space \, and use exponents as necessary. For example,

• \mathrm{m}\,\mathrm{s}^{-2} $\mathrm{m}\,\mathrm{s}^{-2}$
• \mathrm{s}^{-1}\,\mathrm{mol} $\mathrm{s}^{-1}\,\mathrm{mol}$

Examples in Context

\mu_0=4\pi\times10^{-7} \ \left.\mathrm{\mathrm{T}\!\cdot\!\mathrm{m}}\middle/\mathrm{A}\right.

$$\mu_0=4\pi\times10^{-7} \ \left.\mathrm{\mathrm{T}\!\cdot\!\mathrm{m}}\middle/\mathrm{A}\right.$$

180^\circ=\pi \ \mathrm{rad}

$$180^\circ=\pi \ \mathrm{rad}$$

N_A = 6.022\times10^{23} \ \mathrm{mol}^{-1}

$$N_A = 6.022\times10^{23} \ \mathrm{mol}^{-1}$$

Mixing code and MathJax formatting on lines

To give an example of how this might be useful, I wanted to express an algorithm in more or less the same indentation and symbolic way it appears in a paper.

On my desktop browsers (Chrome, Firefox) the following appears reasonably well spaced and indented, but loses indentation on my Android smartphone:

Input: positive integer $n$
Output: Tangent numbers $T_1,\ldots,T_n$
$T_1\gets 1$
for$k$ from $2$ to$n$
$T_k\gets (k−1)T_{k−1}$
for$k$ from $2$ to$n$
for$j$ from$k$ to$n$
$T_j\gets (j −k)T_{j−1} + (j −k+2)T_j$
return $\;T_1,T_2,\ldots,T_n$.

The source can be examined for specific techniques, but the basic trick is that a MathJax dollar-delimiter can follow a closing back-tick code delimiter, but an opening back-tick should be preceded by a space when following the (closing) dollar-sign delimiter.

Here is a version using \phantom rather than code monospacing to produce indents and tweaking the spacing between code and MathJax expressions with \;, so that the results appear clear on Android browsers:

Input: positive integer $n$
Output: Tangent numbers $T_1,\ldots,T_n$
$T_1\gets 1$
for $\;k\;$ from $2\;$ to $\;n$
$\phantom{{}++{}}$ $T_k\gets (k−1)T_{k−1}$
for $\;k\;$ from $2\;$ to $\;n$
$\phantom{{}++{}}$ for $\;j\;$ from $\;k\;$ to $\;n$
$\phantom{{}++{}}$ $\phantom{{}++{}}$ $T_j\gets (j −k)T_{j−1} + (j −k+2)T_j$
return $\;T_1,T_2,\ldots,T_n$.

Markov Chains

This is a heuristic solution for coding Markov chains in Mathjax using a combination of commutative diagrams, the encircle tool and font sizes. There are a few minor issues with this method, for instance the arrows' ends should be attached closer to their targets. Also, it lacks double-headed diagonal arrows and it is difficult to attach probabilities to diagonal arrows. Therefore, it's mostly useful for small chains.

$$ \require{enclose} \begin{array}{ccccccccc} \Large{\enclose{circle}{A}} & \xrightarrow{0.1} & \Large{\enclose{circle}{B}} & \xrightarrow{0.2} & \Large{\enclose{circle}{C}} & \xleftarrow{0.3} & \Large{\enclose{circle}{D}} & \xleftarrow{0.4} & \Large{\enclose{circle}{E}}\\\ \scriptsize{0.5}\large{\downarrow} & \scriptsize{0.6}\large{\searrow} & \scriptsize{0.7}\large{\downarrow} & \scriptsize{0.8}\large{\nearrow} & \scriptsize{0.9}\large{\downarrow} & \scriptsize{0.1}\large{\swarrow} & \scriptsize{0.2}\large{\downarrow} & \scriptsize{0.3}\large{\nwarrow} & \scriptsize{0.4}\large{\downarrow}\\\ \Large{\enclose{circle}{F}} & \xrightarrow[0.5]{} & \Large{\enclose{circle}{G}} & \xrightarrow[0.6]{} & \Large{\enclose{circle}{H}} & \xleftarrow[0.7]{} & \Large{\enclose{circle}{I}} & \xleftarrow[0.8]{} & \Large{\enclose{circle}{J}}\\ \circlearrowright\tfrac12\\ \end{array} $$

\require{enclose}
\begin{array}{ccccccccc}   
\Large{\enclose{circle}{A}} & \xrightarrow{0.1} & \Large{\enclose{circle}{B}} & \xrightarrow{0.2} & \Large{\enclose{circle}{C}} & \xleftarrow{0.3} & \Large{\enclose{circle}{D}} & \xleftarrow{0.4} & \Large{\enclose{circle}{E}}\\\
\scriptsize{0.5}\large{\downarrow} & \scriptsize{0.6}\large{\searrow} & \scriptsize{0.7}\large{\downarrow} & \scriptsize{0.8}\large{\nearrow} & \scriptsize{0.9}\large{\downarrow} & \scriptsize{0.1}\large{\swarrow} & \scriptsize{0.2}\large{\downarrow} & \scriptsize{0.3}\large{\nwarrow} & \scriptsize{0.4}\large{\downarrow}\\\  
\Large{\enclose{circle}{F}} & \xrightarrow[0.5]{} & \Large{\enclose{circle}{G}} & \xrightarrow[0.6]{} & \Large{\enclose{circle}{H}} & \xleftarrow[0.7]{} & \Large{\enclose{circle}{I}} & \xleftarrow[0.8]{} & \Large{\enclose{circle}{J}}\\
\circlearrowright\tfrac12\\ 
\end{array} 

Credit to Zev Chonoles ^[1] for the commutative diagram.

Tables

W/ Sub-Variables

After spending too much time searching for a way to make tables of this form (to no avail), I spent even longer searching for the pieces (of which most were found here ^[1]) to Frankenstein my own. I made this table for a combinatorics q ^[2] on MSE...

$$ \begin{array}{l} \begin{array}{c|c} \hskip36.5pt & \hskip42.5pt\style{font-family:inherit}{\text{Ordering}} \end{array} \\[-7pt]\hline\hskip-5.5pt \begin{array}{c|c|c} \style{font-family:inherit}{\text{Repetition}} & \style{font-family:inherit}{\text{w/}} & \style{font-family:inherit}{\text{w/o}} \\\hline \style{font-family:inherit}{\text{w/}} & P_r^n=n^r & C_r^n=\left(\!\left(\begin{smallmatrix} n \\ r \end{smallmatrix}\right)\!\right)=\left(\begin{smallmatrix} n+r-1 \\ r \end{smallmatrix}\right) \\[0pt]\hline \style{font-family:inherit}{\text{w/o}} & nPr=\frac{n!}{(n-r)!} & nCr=\left(\begin{smallmatrix} n \\ r \end{smallmatrix}\right)=\frac{n!}{r!(n-r)!} \end{array}\hskip-5.5pt \end{array} $$

W/o Sub-Variables

While searching, I found several tables of this form...

$$ \begin{array}{c|c|c|c} \style{font-family:inherit}{\text{Day}} & \style{font-family:inherit}{\text{Credit}} & \style{font-family:inherit}{\text{Debit}} & \style{font-family:inherit}{\text{Total}}\\\hline 0 & 0 & 0 & 10000 \\\hline 1 & 100 & 500 & 9600 \\\hline 2 & 0 & 400 & 10000 \\\hline 3 & 1000 & 500 & 10500 \end{array} $$

Overlaying symbols

_{(using negative spacing)}

To overlay the $\wedge$ \wedge and the $\bigcirc$ \bigcirc, to make the Kulkarni Nomizu Product ^[1]:

$$\mathbin{\rlap{\,\wedge}\bigcirc}$$

Which is \mathbin{\rlap{\,\wedge}\bigcirc}.

Just for another example: Overlaying of $\}$ \} and $\div$ \div: $$\rlap{\,\,\}}\div$$

Which is \rlap{\,\,\}}\div.

The command \rlap{c1}c2 prints the character c1 with zero-width on the right-hand side of the current position, so that c2 overlaps with c1. In practice, you might want to

1. choose the widest character as c2
2. adjust the horizontal spacing by prepending c1 with extra horizontal space \,.
3. if necessary, wrap up the symbol with \mathbin so that MathJax treats the symbol like an operator, and the spacing around the symbol is correct.

As you can see, the number of \! is different, for exact overlaying of each symbol. \! makes the characters left and right to it move a little bit closer.

e.g, the code ab produces $ab$.
And the code a\!b produces $a\!b$

Tensor indices

T^{\alpha\beta}{}_{\gamma\delta}

$T^{\alpha\beta}{}_{\gamma\delta}$

T^{\alpha \beta}{}_{\gamma\delta}{}^{\lambda}

$T^{\alpha \beta}{}_{\gamma\delta}{}^{\lambda}$

So for instance, a $(2,2)$-tensor would act on two covectors ($\omega$, $\varphi$) and two vectors ($v$,$w$) to produce a real number like this:

$$[T^{\alpha \beta}{}_{\gamma\delta}e_\alpha\otimes e_\beta\otimes e^\gamma \otimes e^\delta](\omega,\varphi,v,w).$$

Is there a way to make the Greek letters displayed upright (non-italic)?

Asked in comment. There is a way using unicode characters, for which one can search here: http://unicode-table.com/en. Normal use of phi is $\phi = ...$, which gives $\phi = ...$.
Looking up phi on the above site gives a couple of results, if one uses 'Greek Capital Letter Phi' and copy it with the button below its picture, and use it like
$Φ = ...$, the result is $Φ = ...$.
One might need to experiment which symbol(s) look(s) right.

Is there a tool to visually edit (prepare) the formulas with pre-defined symbols and paste here?

For some of the formulas one can use a word processor app that supports formula edition. E.g. one can use MS Word to construct the formula, or even better use the existing pre-defined ones, like I did with the Binomial theorem, then simply select it, and copy-paste here between the desired number of $'s:

$$ \left(x+a\right)^n=\sum_{k=0}^{n}{\binom{n}{k}x^ka^{n-k}} $$

If it does not look right, it might still be less time to adjust the expression than starting it from scratch, or trying to draw by hand such a thing like the above.

Evaluated at (integrals):

To get a vertical bar to the right of an expression with the limits of integration, expressions such as $\Big |$$\Big |$ result in one-size-fits-all outputs.

\left. \right|_{}^{} works well as in the made up expression below to illustrate this feature:

$$\left. \left(3x\left(\frac{\left(\log(\frac{3x^2}{6}\right)^{\frac{-x^2}{8}}}{3x^{1/2}} \right) \right) \right|_{\;x=2}^{\;x=8}$$

Alternative Ways of Writing in $\Large\LaTeX$

TYPESET FONTS

As mentioned before, you can write $\mathtt{. . .}$ to generate fonts like $\mathtt{A}$, $\mathtt{B}$, $\mathtt{C}$ and etc.

You can also produce these fonts writing $\verb|. . .|$ which generates the same fonts $\verb|A|$, $\verb|B|$, $\verb|C|$ and etc.

And concerning different “angle fonts”, $\angle$ generates $\angle$, $\measuredangle$ generates $\measuredangle$ and last but not least, $\sphericalangle$ generates $\sphericalangle$. Also, $\langle...\rangle$ generates $\langle...\rangle$.

Concerning different “approximation fonts”, $\approx$ generates $\approx$ with $\thickapprox$ generating $\thickapprox$. In addition to that, $\sim$ generates $\sim$ and $\thicksim$ generates $\thicksim$ with $\backsim$ generating $\backsim$.

For a symbol of contradiction, you can write $\Rightarrow\Leftarrow$ to generate $\Rightarrow\Leftarrow$ or you can write $\unicode{x21af}$ to generate $\unicode{x21af}$, which is read as Scar (short for Harry Potter's scar, explaining why it looks like a lightning bolt).

$$***$$

INEQUALITY SIGNS

You can write $\lt$ or $<$ to generate $<$ and $\gt$ or $>$ to generate $>$, with $\le$ or $\leq$ to generate $\leq$.

You can also produce similar less than inequality signs with $\leqslant$ to generate $\leqslant$ and $\leqq$ to generate $\leqq$. The same applies for greater than inequality signs, for which we just rewrite the command as $\g...$ instead of $\l...$ which produces $\geq$, $\geqslant$ and $\geqq$.

By putting in an n, we could form commands like $\ngtr$ to generate $\ngtr$ and $\nless$ to generate $\nless$ as opposed to $\not>$ and $\not<$.

Also, $\ngeq$ = $\not\geq$ which generates $\ngeq$ and $\nleq$ = $\not\leq$, generating $\nleq$.

Furthermore, putting slant at the end of strictly the previous two commands generates $\ngeqslant$ and $\nleqslant$.

$$***$$

SET CONTAINMENT

You could write $\not\subseteq$ to generate $\not\subseteq$ or $\not\supseteq$ to generate $\not\supseteq$.

You can write $\subsetneq$ to generate $\subsetneq$ and $\supsetneq$ to generate $\supsetneq$.

Or, you can write $\subsetneqq$ to generate $\subsetneqq$ and $\supsetneqq$ to generate $\supsetneqq$.

By striking out the n in the previous commands with qq at the end, we can generate $\subseteqq$ and $\supseteqq$.

Instead of $\left\{. . .\right\}$ to generate $\left\{...\right\}$, you can write $\lbrace...\rbrace$ to generate the exact same thing. For sets that contain element(s) with a single number or letter, you can also write $\{. . .\}$ to generate strictly $\{. . .\}$ with no other smaller or larger brace sizes.

As another alternative to denoting the difference of two sets $A$ and $B$, you can write $\diagdown$ to generate $\diagdown$ in the set expression, $A\diagdown B$. This command though is mainly used for sets $A^n$ and $B^n$. There also exists $\diagup$ = $\diagup$ by the way to denote the division operation as opposed to the ordinary / or $\div$ = $\div$. $$***$$

OLD-STYLE

For old-style notation, you can write $\eqslantless$ to generate $\eqslantless$ and $\eqslantgtr$ to generate $\eqslantgtr$. These notations can be used to mean the same as $\leqslant$ and $\geqslant$ which is also the same as $\leq$ and $\geq$, but if used today, they commonly represent a not much less than or not much greater than inequality sign.

If you want to write that the statement, $x > y$ and thus $x\neq y$, without any words, then you can write $x \gvertneqq y$ to generate $x \gvertneqq y$. If, on the other hand, you want to then write the same statement for $x < y$ then you can write $x \lvertneqq y$ to generate $x \lvertneqq y$.

Suppose you have that $x\in \mathbb{R}$ but $x \neq 0$ $(\star)$ for example (like in this question ^[1]), one could write it as follows: $x\in\mathbb{R}\setminus\{0\}$ with $\setminus$ to generate $\backslash$. There is an alternative way of writing $(\star)$, nonetheless.

You can write $\gtrless$ to generate $\gtrless$ which means less than and greater than. If $x\gtrless y$ then $x$ is equal to a number greater than $y$ or less than $y$. Therefore, $x \in\mathbb{R}\setminus\{0\}$ can also be written as $x\gtrless 0$. You can also write $\lessgtr$ to generate $\lessgtr$ which essentially means the same thing. The following commands and notation is unnecessary, for their definition is obvious.

$\gtreqless$ generates $\gtreqless$ and $\lesseqgtr$ generates $\lesseqgtr$.

$\gtreqqless$ generates $\gtreqqless$ and $\lesseqgtr$ generates $\lesseqqgtr$.

How to draw a stretched vertical bar to indicate the bounds (upper and lower limits) after taking the anti-derivative of a definite integral

I'd like to also expound upon bullet 6 in the question, about parenthesis. I originally put my edit into the question there, but the primary editor of the question reverted my edits. I and others need this information and a good example, so here it is:

There are also invisible parentheses, denoted by ., as in \left. or \right.. These can take the place of any type of parenthesis whether it be (, [, or something else. Ex: \left.\frac12\right\rbrace is $\left.\frac12\right\rbrace$, and \left.\frac12\right) is $\left.\frac12\right)$.

To stretch a vertical bar to be tall, such as to plug in upper and lower limit values into a definite integral's antiderivative, add an invisible vertical bar on the left with \left., and a visible vertical bar on the right with \right|. For lower and upper limits of 0 and 4, respectively, the lower limit is set with _{\;0}, and the upper limit with ^{\;4}, where the \; is a wider space to shift the numbers to the right of the vertical bar.

Example: $$\left.{\left[\cfrac{x}{\cfrac{a+b}{c}}\right]}\right|_{\;0}^{\;4}$$ produces:

$$\left.{\left[\cfrac{x}{\cfrac{a+b}{c}}\right]}\right|_{\;0}^{\;4}$$

See also:

1. This answer I just saw after writing all this: Evaluated at (integrals) ^[1]