How can I change the font size in math equations?

Question

I find that whenever I'm typing some equations into a document, and the equation gets a bit complex (let's say a fraction in a parentheses, squared, inside a square root, inside a fraction), the variables and whatnot that I put inside the "inner" parts of the equation get really, really, tiny. But if I set the font size to something a lot larger, the stuff on the "inside" gets tolerable, but the stuff on the "outside" (e.g., "x = lots of junk", x would be in the "outside") become gigantic!

How can I make it more pretty like my textbooks, where all variables are at the same size regardless of whatever parentheses/fractions/radicals they're under?

Answer 1

To get equal sizes, you could use \DeclareMathSizes in your preamble. The syntax is

\DeclareMathSizes{display size}{text size}{script size}{scriptscript size}.

You could simply set all to your default font size. In this example:

\documentclass[10pt]{article}
\begin{document}
\[
  x = \frac{1}{x + \frac{1}{x + \frac{1}{x}}}
\]
\end{document}

where you firstly get different sizes:

inserting this line

\DeclareMathSizes{10}{10}{10}{10}

changes the output to:

Answer 2

You can try \dfrac instead of \frac.

Answer 3

Put this in your preamble, but after all \usepackage commands:

\everymath=\expandafter{\the\everymath\displaystyle}

This will effectively add \displaystyle to every (inline) math made environment, making all math look like the math that's displayed.

Edits: Thanks to Charles for pointing out that this can/should be done in a way which doesn't clobber the existing \everymath token list, in case it's already nonempty. And as Willie says the = is optional. I like using it; it just reminds me that there is some assignment going on.

Edit 2: The OP asked for a detailed explanation. I'll try.

First, remember that \everymath is a token list that is inserted in front of every math mode material. So if you type \everymath={\text{Here comes the math: }} you will get that in front of every equation. \everymath={\displaystyle} does something a little more productive by inserting \displaystyle in front of each math mode.

The trouble arises when you or some other package has already modified \everymath. So we need to append \displaystyle to the \everymath token list. In pseudo-TeX you want to say:

\everymath={\currentcontentsof{\everymath}\displaystyle}

The TeX implementation of the pseudo-macro \currentcontentsof is \the. So a closer approximation is this:

\everymath={\the\everymath\displaystyle}

But this is going to be trouble, When TeX reads a token list declaration it just reads the tokens without expanding. That is, the \the will be expanded not here but at the the first encountered math mode. That will cause TeX to try to expand \everymath, which will need an expansion of \everymath inside it. Oops! Infinite loop.

So you need the \the expanded before you save the token list. Hence \expandafter:

\everymath=\expandafter{\the\everymath\displaystyle}

When TeX reads \everymath=, it expects a token list. But instead, it gets \expandafter, which says "hold on to the next token, expand the following token, then put the held token back in place and expand normally." So the { token is deferred while \the is expanded. \the needs another token to work, so the next token \everymath is read. This replaces the two tokens \the\everymath with the tokens currently in \everymath. Now that { is put back in place, and TeX can read a normal token list declaration.

Other TeXnicians may correct that answer, but it's how I understand things.

Answer 4

You can use \everymath locally by inserting \begingroup and \endgroup as this

\begingroup
\everymath{\scriptstyle}
\scriptsize
%your equation
\endgroup