[Tex/LaTex] 1.5e-10 style scientific notation looks ugly in LaTeX math mode. How to format it (kerning, etc) more nicely

Question

I've noticed that e-style (for example, 1.5e-10) scientific notation does not look especially nice in Latex math mode:

(code used to generate the above image: $1.5e-10$)

In particular, the width and kerning of the negative sign is totally off. Is there any way to specifically fix the issues with the negative sign?

My LaTeX code:

Here's the complete code, including packages, for the above image:

\documentclass[11pt,notitlepage]{article}
\usepackage{amsfonts, amsmath, amsthm, amssymb}
\begin{document}
$1.5e-10$
\end{document}

I've also run into the exact same kerning issues with MathJax (via the markdown editor in IPython Notebook. Notebook sets MathJax up automatically, so no idea what packages they use).

Context: floating point numbers and numerical programming

For context, when I originally asked this question I was writing a tutorial about the mathematics of stochastic simulation, with the goal of teaching people how to implement their own simulations in Python. This particular notation (<significand>e[<sign>]<exponent>) is relevant since it's how you write a floating point literal (ie a symbol that the Python interpreter understands as representing a particular floating point number). The <signficand>*<base>^<exponent> notation and its prettier variants are less appropriate, since Python (and many other languages) don't recognize it.

Answer 1

It's not ugly, but exactly what's expected. If you type

$2x-10$

then you expect that there is some space around the minus sign, because it denotes an operation. When you type $1e-10$, TeX interprets it in exactly the same way, because it can't read your mind: the two expressions are formally the same, only two symbols are different.

If you want that an expression that's normally interpreted as a polynomial should be treated in a different way, then you have to properly mark it.

One solution might be

$1\mathrm{e}{-10}$

because in this case the braces around -10 tell TeX to enter a subformula and so the minus sign is initial, so not interpreted as a binary operation, but as a unary operator.

You could make a definition, such as

\newcommand{\expnumber}[2]{{#1}\mathrm{e}{#2}}

and input the number as

$\expnumber{1}{-10}$

but there's a much better alternative, the package siunitx.

\documentclass{article}

\usepackage{siunitx}
\sisetup{output-exponent-marker=\ensuremath{\mathrm{e}}}

\begin{document}

\num{1e-10}

\end{document}

This package offers many more features than just printing numbers in the desired format; consult its documentation to find them.

---

Note that siunitx is not understood by MathJax, so with it you must stick to the “hand made” solution. You can still say, in it,

$\def\num#1{\numx#1}\def\numx#1e#2{{#1}\mathrm{e}{#2}}$ 

and a formula such as $\num{1e-10}$ will be printed in the way you want.