\documentclass{article}
\usepackage{fullpage}

\title{Sample Performance Study}
\author{High Performance Computing Facility\\University of Maryland, Baltimore County}
\date{}

\begin{document}
\maketitle

\begin{table}[h]
\centering
\caption{Wall clock time in seconds
for problems of size $N$
using 1, 2, 4, 8, 16, 32 compute nodes
with 1, 2, 4, and 8 processes per node.}
\label{tab:summary}
\begin{tabular}{lrrrrrr}
\hline
\multicolumn{1}{l}{(a) $N = 1024$} &
\multicolumn{1}{r}{ 1 node } &
\multicolumn{1}{r}{ 2 nodes} &
\multicolumn{1}{r}{ 4 nodes} &
\multicolumn{1}{r}{ 8 nodes} &
\multicolumn{1}{r}{16 nodes} &
\multicolumn{1}{r}{32 nodes} \\
\hline
1 process   per node& 00:17:04  & 00:08:32  & 00:04:16  & 00:02:08  & 00:01:04  & 00:00:32  \\
2 processes per node& 00:08:32  & 00:04:16  & 00:02:08  & 00:01:04  & 00:00:32  & 00:00:16  \\
4 processes per node& 00:04:16  & 00:02:08  & 00:01:04  & 00:00:32  & 00:00:16  & 00:00:08  \\
8 processes per node& 00:02:08  & 00:01:04  & 00:00:32  & 00:00:16  & 00:00:08  & 00:00:04  \\
\hline
\hline
\multicolumn{1}{l}{(b) $N = 2048$} &
\multicolumn{1}{r}{ 1 node } &
\multicolumn{1}{r}{ 2 nodes} &
\multicolumn{1}{r}{ 4 nodes} &
\multicolumn{1}{r}{ 8 nodes} &
\multicolumn{1}{r}{16 nodes} &
\multicolumn{1}{r}{32 nodes} \\
\hline
1 process   per node& 00:34:08  & 00:17:04  & 00:08:32  & 00:04:16  & 00:02:08  & 00:01:04  \\
2 processes per node& 00:17:04  & 00:08:32  & 00:04:16  & 00:02:08  & 00:01:04  & 00:00:32  \\
4 processes per node& 00:08:32  & 00:04:16  & 00:02:08  & 00:01:04  & 00:00:32  & 00:00:16  \\
8 processes per node& 00:04:16  & 00:02:08  & 00:01:04  & 00:00:32  & 00:00:16  & 00:00:08  \\
\hline
\hline
\multicolumn{1}{l}{(c) $N = 4096$} &
\multicolumn{1}{r}{ 1 node } &
\multicolumn{1}{r}{ 2 nodes} &
\multicolumn{1}{r}{ 4 nodes} &
\multicolumn{1}{r}{ 8 nodes} &
\multicolumn{1}{r}{16 nodes} &
\multicolumn{1}{r}{32 nodes} \\
\hline
1 process   per node& 01:08:16  & 00:34:08  & 00:17:04  & 00:08:32  & 00:04:16  & 00:02:08  \\
2 processes per node& 00:34:08  & 00:17:04  & 00:08:32  & 00:04:16  & 00:02:08  & 00:01:04  \\
4 processes per node& 00:17:04  & 00:08:32  & 00:04:16  & 00:02:08  & 00:01:04  & 00:00:32  \\
8 processes per node& 00:08:32  & 00:04:16  & 00:02:08  & 00:01:04  &      ---  &      ---  \\
\hline
\end{tabular}
\end{table}

\end{document}
