formula width in double column paper

Question

I have a formula which has a content like below..

\documentclass[journal]{IEEEtran}
\usepackage[backend=biber]{biblatex}
\addbibresource{bibliography.bib} %Import the bibliography file
\usepackage{lipsum}
\usepackage{algpseudocode}
\usepackage{algorithm}
\usepackage{graphicx}
\usepackage{adjustbox}
\hyphenation{op-tical net-works semi-conduc-tor}
\usepackage{amsmath,amssymb}
\DeclareRobustCommand{\bbone}{\text{\usefont{U}{bbold}{m}{n}1}}
\DeclareMathOperator{\EX}{\mathbb{E}}
\DeclareMathOperator{\E}{\mathbb{E}}
\begin{document}
\maketitle
\lipsum
\begin{equation}
\begin{aligned}[c]
reward(node, action)  = \begin{cases}
    constant_action_reward -\par action_cost +
    success_prob(action, sequence) * node_reward,& \text{if } "XXX"=action
    constant_action_taking_reward - action_cost, & \text{otherwise}
\end{cases}
\end{aligned}
\end{equation}
\lipsum
\end{document}

I tried this both in double column using the * like {equation*} and not. Paper is double column. In each option, this covers a two column and other text comes over this. I attached a sample picture. I would be happy if it fits a single column or at least it covers a double column and no text comes over it.

Answer 1

As Zarko commented your equation wouldn't fit even if you use double-column.

The first option, which I think is the best, is to use shorter variable names.

If you must use the formula exactly as it appears, Zarko suggested you break the first line of the cases. I think it looks better instead of you break before the cases. (And you should display this with the full text width: in one column using the variable names as they stand there is no way to display your equation in fewer than 5 lines, which makes it not very legible.)

\documentclass[journal]{IEEEtran}
\usepackage[backend=biber]{biblatex}
\addbibresource{bibliography.bib} %Import the bibliography file
\usepackage{lipsum}
\usepackage{graphicx}
\usepackage{adjustbox}
\hyphenation{op-tical net-works semi-conduc-tor}
\usepackage{amsmath,amssymb}
\begin{document}
\lipsum
\begin{equation}
    E = mc^2
\end{equation}
\begin{figure}[!t]
\normalsize
\begin{multline}
    \mathsf{reward(node, action)}  = \
    \begin{cases}
        \mathsf{constant_action_reward} - \mathsf{action_cost} +
        \mathsf{success_prob(action, sequence)}  \mathsf{node_reward},& \text{if ``XXX''=action}  \
        \mathsf{constant_action_taking_reward} - \mathsf{action_cost}, & \text{otherwise}
\end{cases}
\end{multline}
\hrulefill
% The spacer can be tweaked to stop underfull vboxes.
\vspace{4pt}
\end{figure}
\begin{equation}
    E = mc^e
\end{equation}
\lipsum
\end{document}

Some notes:

1. I wrapped your variable names in \mathsf since they look like computer variable names. If they were words I would use \mathrm or \mathit as David Carlisle suggested.
2. There are some other small mistakes in the displayed equation that I fixed.
3. I have no idea what the semantic meaning of "XXX"=action is, so I left them as text. But you should adjust to fit the meaning.
4. If you compile this document, you will see that the the equation is numbered out of order. This is "by design": the IEEEtran documentation indicates a preference for double-column equations to be floated to the top of the next page. The code included in the documentation provides a way to restore the correct numbering; but this requires manual intervention and should be set AFTER you finished your entire document. So I omit that in the code above.

Answer 2

First of all you should use a Times compatible font also for math and also wrap your long names in \mathit or similar.

Second, you need to split the long top line. Using cases is out of the question, I'm afraid.

A bit of visual formatting helps.

\documentclass[journal]{IEEEtran}
\usepackage{amsmath,mathtools,amssymb}
\usepackage{newtx} % for math symbol compatible with Times
\usepackage{lipsum}
\newcommand{\tv}[1]{\mathit{#1}} % text variable
\begin{document}
\lipsum[1][1-4]
\begin{equation}
\hspace{-0.5em}
\begin{aligned}
&\tv{reward}(\tv{node}, \tv{action}) \
& =
\left{
  \begin{aligned}
    &\begin{aligned}
      \begin{aligned}
        &\tv{constant_action_reward} - \tv{action_cost} \
        &+ \tv{success_prob}(\tv{action}, \tv{sequence}) \cdot \tv{node_reward},
      \end{aligned}
      \
      \text{if } \text{"XXX"}=\tv{action}\hspace{-0.3em}
    \end{aligned}
  \[2ex]
    &\begin{aligned}
      \tv{constant_action_taking_reward} - \tv{action_cost},
      \
      \text{otherwise}\hspace{-1em}
    \end{aligned}
  \end{aligned}\right.
\end{aligned}
\hspace{1000pt minus 1fil}
\end{equation}
\lipsum
\end{document}