سلام
ردیف دوم به بعد را با multirow نوشتید.
ولی خطی بعد از اون وجود نداره باهاش merge بشه.
یک راهش (بدون اینکه به سلوهای شمادست بزنم) اینه کافیه یک خط بعدش اضافه کنین.
\documentclass[review]{elsarticle}
\usepackage{lineno,hyperref}
\usepackage{amsmath,amssymb}
\usepackage{tabularx}
\usepackage{multirow}
\usepackage[utf8]{inputenc}
\usepackage{graphicx}
\usepackage{caption}
\usepackage[table]{xcolor}
\usepackage{colortbl}
\usepackage{float}
\usepackage{array}
\usepackage{lscape}
%\usepackage{cite}
\newcolumntype{b}{>{\hsize=3.7\hsize}X}
\newcolumntype{s}{>{\hsize=2\hsize}X}
\newcolumntype{m}{>{\hsize=3.1\hsize}X}
\begin{document}
\begin{table}[h!]
\caption{Results of AFSA and GWA for K=10 under certain condition }\label{tbl2}
\centering
\begin{tabularx}{\textwidth}{|b|bbbm|bbbm|}
\cline{1-9}
% after \\: \hline or \cline{col1-col2} \cline{col3-col4} ...
\multirow{3}{3cm}{Risk \\aversion\\ coefficient}&\multicolumn{4}{c}{AFSA}&\multicolumn{4}{|c|}{GWA}\\
\cline{2-9}
&\multirow{2}{4cm}{Total \\portfolio \\return\\}&\multirow{2}{4cm}{Total\\ portfolio \\risk\\}&Objective value&Solution time&\multirow{2}{4cm}{Total\\ portfolio\\ return\\} &\multirow{2}{4cm}{Total\\ portfolio\\ risk\\}&Objective value&Solution time\\
&&&&&&&&
\\ \cline{1-9}
0.0&1.31&0.72&-58.13&1.27&1.30&0.70&-56.10&0.96\\
0.1&1.21&0.69&-50.29&1.40&1.20&0.60&-50.19&1.40\\
0.2&1.19&0.63&-40.59&2.16&1.18&0.50&-40.05&3.19\\
0.3&1.09&0.55&-34.56&3.76&1.08&0.47&-32.10&4.22\\
0.4&1.07&0.52&-27.42&5.49&1.06&0.45&-26.27&5.97\\
0.5&1.03&0.48&-19.05&6.19&1.02&0.44&-18.88&7.62\\
0.6&0.97&0.44&-12.11&10.37&0.96&0.44&-11.06&8.19\\
0.7&0.88&0.44&-4.52&11.29&0.88&0.44&-4.23&10.07\\
0.8&0.88&0.44&2.10&13.96&0.88&0.44&2.91&11.27\\
0.9&0.82&0.42&8.90&15.79&0.81&0.42&8.71&13.96\\
1.0&0.81&0.40&14.24&18.96&0.80&0.40&14.14&15.84\\
Mean&1.02&0.52&-20.04&8.24&1.01&0.48&-19.53&7.52\\
\end{tabularx}
\end{table}
\end{document}
\endinput
%%
%% End of file `elsarticle-template-harv.tex'.
خروجی:
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