Caption centering does not work

Question

I am using subcaption package to plot subfloats in my report. However, the caption for subfigures are not centered. Here is what I have done:

\documentclass[10pt]{report}
\usepackage{epsfig,cite,amsfonts,amssymb,psfrag,balance}
\usepackage[centertags]{amsmath}
\usepackage{amsthm}
\usepackage{newlfont}
\usepackage[ansinew]{inputenc}
\usepackage[justification=centering]{caption}
\usepackage{graphicx,subcaption}
\usepackage{dsfont}
\usepackage{morefloats}

\begin{subfigure}{0.33\textwidth}
    \centering
    \psfrag{lambda}[][][1.5]{$\log_{10} (\lambda)$}
    \psfrag{N}[][][1.5]{Channel Noise Power, $N$}
    \resizebox{8cm}{!}{\epsfbox{P3_N_vary.eps}}
    \caption{Achievable}
    \label{fig:p3_graph1}
\end{subfigure}
\hspace{2.5cm}
\begin{subfigure}{0.33\textwidth}
    \centering
    \psfrag{lambda}[][][1.5]{$\log_{10} (\lambda)$}
    \psfrag{Ps}[][][1.5]{Encoder transmit power, $\ps$}
    \resizebox{8cm}{!}{\epsfbox{P3_ps_vary.eps}}
    \caption{Achievable }
    \label{fig:p3_graph2}
\end{subfigure}
\caption{}
\end{figure}

Am I missing something here? Can somebody help me out please?

Answer 1

Assuming you're using a "standard" paper size (either letterpaper or A4) and "normal" horizontal margins (ca. 1"), your document's \textwidth parameter will be equal to roughly 6" (15cm). You allocate an overall width to each subfigure environments of 0.33\textwidth, which works out to about 2" (5cm). Yet, via the \resizebox instructions, you specify a display width of 8cm for the included graphics. These parameters are not mutually consistent, and thus LaTeX can't perform the centering as requested.

To fix up the problem, you may try applying the following changes: (i) specify widths of each subfigure of 0.45\textwidth instead 0.33\textwidth, (ii) use \linewidth instead of 8cm as the first argument of the \resizebox instructions, and (iii) replace the instruction \hspace{2.5cm} with \hspace{\fill}.