How to fix "Underfull \hbox (badness 10000) in paragraph " in a two-column format?

Question

How can I fix this warning? I read that it can be ignored in most of cases but I want to fix it.

Underfull \hbox (badness 10000) in paragraph at lines 16--17

\documentclass[lettersize,journal]{IEEEtran}
\usepackage{amsmath,amsfonts}
\usepackage{algorithmic}
\usepackage{algorithm}
\usepackage{array}
\usepackage[caption=false,font=normalsize,labelfont=sf,textfont=sf]{subfig}
\usepackage{textcomp}
\usepackage{stfloats}
\usepackage{url}
\usepackage{verbatim}
\usepackage{graphicx}
\usepackage{cite}
\begin{document}

\section{Introduction}
Two lists $(x_5,y_9,z_3,t_1,m_8,n_3,q_9,k_6)$ and $(x_4,y_2,z_4,t_1,m_5,n_3,q_9,k_2)$ have the same size and same forms.
\end{document}

Another question is about "Unused global option(s)". What options specificly are they talking about here?
This is the warnings I got when I ran that code. (I'm using overleaf if that make it different)

Answer 1

1. You should allowed that your list can be broken. For possible ways see answers on question allowing-line-break-at-in-inline-math-mode.

2. Not used global option is lettersize in documentclass options.

Possible MWE, which solve your problems, is:

\documentclass[journal]{IEEEtran}
\usepackage{amsmath,amsfonts}
\usepackage{algorithmic}
\usepackage{algorithm}
\usepackage{array}
\usepackage[caption=false,font=normalsize,labelfont=sf,textfont=sf]{subfig}
\usepackage{textcomp}
\usepackage{stfloats}
\usepackage{url}
\usepackage{verbatim}
\usepackage{graphicx}
\usepackage{cite}

\makeatletter       % stolen from https://tex.stackexchange.com/questions/1959/
                    % allowing-line-break-at-in-inline-math-mode
\def\old@comma{,}
\catcode`\,=13
\def,{%
  \ifmmode%
    \old@comma\discretionary{}{}{}%
  \else%
    \old@comma%
  \fi%
}
\makeatother

\begin{document}

\section{Introduction}
Two lists $(x_5,y_9, z_3,t_1, m_8,n_3, q_9,k_6)$ and $(x_4,y_2, z_4,t_1, m_5,n_3, q_9,k_2)$ have the same size and same forms.
\end{document}