Parenthesis {} are not occurring.Also in first D/2 ,2 is very large.+1,+2 are also very large not subscript type.
Code: Select all
\documentclass[12pt,journal,compsoc]{IEEEtran}
\usepackage{alltt}
\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{mathtools}
\usepackage{array}
\usepackage{amsmath}
\usepackage{graphicx}
\usepackage{float}
\usepackage{lipsum}
\begin{document}
{
$D_(m/2)+1$,$D(m/2)+2$,...,$D_m$
}
\end{document}