How many font styles of $x$ and $X$ can we use?

Question

I want to use different variable styles in my dissertation. I'm currently using $x$ for a single random variable, $\mathbf{x}$ for a set of random variables and $\mathcal{X}$ for a state space. I also need to use 2D/3D variables in a different chapter. How could I define them? I already know:

$x$
$\mathbf{x}$
$\mathrm{x}$
$\mathds{X}$
$\mathcal{X}$

but $\mathbf{x}$ and $\mathrm{x}$ are not very different.

Answer 1

Here’s a list of some fonts:

• second \mathcal requires eucal package
• \mathbb requires amsfonts package
• \mathscrrequires mathrsfs package
• not all of them support lowercase and/or greek letters
• \mathtt is misisng in the image

But I strongly recommend not to use them directly but instead define a new markup macro like

\newcommand*{\StateSpace}[1]{\mathcal{#1}}

and then use it like

$\StateSpace{X}$

(shorter names are certainly possible, like \stsp{X})

Doing this would be in the sense of TeX’s separation of content/structure and design/layout, i.e. logical markup instead of fixed formatting. Furthermore in this case it is easy to change the appearance later constant win the whole document, for example if your editor/publisher wants another style.

---

Can I use \mathsf{A} in bold??

If you got only latin letters (or a text font supporting greek) you could use the text font for this and define

\newcommand*{\myvar}[1]{%
   \mathord{\mbox{%
      \sffamily\bfseries\itshape
      #1%
   }}%
}

(I added also \itshape because usually variable are set in italics.)

Another way is to define a new math alphabet: Bold , italic (and sans-serif) math symbols

---

How can I also incorporate a subscript in the \newcommand that you defined?

First, a note: It should be $\myvar{X}_{test}$ (the subscript outside of the variable argument). Furthermore If the subscript is a text like “max”, “eff.”, “min” etc. you should use \text from amsmath package! Only if the subscript is a variable itself (n, i, …) or a number you should write it like x_i.

If the subscript is always the same (text) you could just add it to the above definition:

\usepackage{amsmath}
\newcommand*{\myvar}[1]{%
   \mathord{\mbox{%
      \sffamily\bfseries\itshape
      #1%
   }}%
   _{\mkern2mu\text{text}}%
}

(The \mkern2mu part insert a little space to shift the subscript a little to the right, which looks better.)

If you always have a subscript but a different one each time you can add a second mandatory argument:

\usepackage{amsmath}
\newcommand*{\myvar}[2]{%
   \mathord{\mbox{%
      \sffamily\bfseries\itshape
      #1%
   }}%
   _{\mkern2mu\text{#2}}%
}

and use it like $\myvar{X}{test}$.

If the subscript is optional you could use an optional argument which could be defined with \newcommand too but the test for an empty argument is easier with \NewDocumentCommand form the xparse package:

\usepackage{amsmath,xparse}
\NewDocumentCommand{\myvar}{ o m }{
   \mathord{\mbox{%
      \sffamily\bfseries\itshape
      #2%
   }}%
   \IfValueT{#1}{_{\mkern2mu\text{#1}}}%
}

and use it like $\myvar{X}$or $\myvar[test]{X}$. It is also possible to change the order of the arguments by replacing o m with m o, #1 with #2 and vice versa. Then the second argument would be optional but it could be problematic if the major without optional argument should be followed by a bracket.