Writing the code

The weight decay was set to $1 \times {10^{−4}}$ for Model 8 and $5\times 10^{−4}$.


the negative sign is missing.

And these are the packages I'm using

\usepackage{jmlr2e}
\usepackage{indentfirst}
% Definitions of handy macros can go here
\usepackage{float}
\usepackage{underscore}
\restylefloat{table}
\newcommand{\dataset}{{\cal D}}
\newcommand{\fracpartial}[2]{\frac{\partial #1}{\partial  #2}}

• Please give a minimal working sample. – Mogic Dec 15 '17 at 6:39
• By the way, the \cal command has been deprecated for 25 years. It should be \mathcal{D} rather than {\cal D} – egreg Dec 15 '17 at 7:10

The problem occurs because the symbol − that's used in both exponents is not a "normal" dash symbol, -. Instead, it is the Unicode symbol U+2212, the "math minus" symbol. (Did you maybe copy and paste the input from some other source?)

Here are three remedies:

• Switch to either XeLaTeX or LuaLaTeX and load either the fontspec package or the unicode-math package (which loads fontspec automatically).

• If you need to use pdfLaTeX, add the following instructions to your preamble:

\usepackage[utf8]{inputenc}
\DeclareUnicodeCharacter{2212}{-}

• Finally, consider simply replacing all instances of − with -. (That's what's done in the code below.)

\documentclass{article}

\begin{document}

The weight decay was set to $1 \times {10^{−4}}$ for Model 8 and $5 \times 10^{−4}$.

\bigskip

\section*{Correct code}
The weight decay was set to $1 \times {10^{-4}}$ for Model 8 and $5 \times 10^{-4}$.

\end{document}

• I've taken the liberty of augmenting your answer a bit. :-) – Mico Dec 15 '17 at 7:26
• @Mico It's perfect to me. Thank you for improving my answer with your original contribution, I really appreciate that. ;-) – Cragfelt Dec 15 '17 at 9:09
• Just to be fussy: I wouldn't write that - is a normal dash: this might be confusing as it recalls the en and the em dash. The correct name, I believe, is hyphen. – campa Dec 15 '17 at 16:45

I fixed your codes as follows:

The weight decay was set to $1 \times {10^{-4}}$ for Model 8 and $5\times 10^{-4}$.


And the following is the PDF style.

The reason that why your − can't be complied may be that you type it not in English typewriting. Please make sure you are under English typewriting when you type codes in math environment.

• I wouldn't emphasize the "English" aspect. The exact same problem is going to occur if the document is in French, German, Italian, ... – Mico Dec 15 '17 at 6:48
• Hopefully needless to say, the preceding comment was not supposed to slight users of Spanish, Portuguese, Norwegian, Swedish, Finnish, Polish, etc, etc, etc. – Mico Dec 15 '17 at 7:27

shorter and correct with use siunitx package:

\documentclass{article}
\usepackage{siunitx}

\begin{document}
The weight decay was set to \num{1e-4} for Model 8 and \num{5e-4}.
\end{document}