The error message you get informs you about \multirow
being undefined. Most likely this is the case because you did not load the multirow
package.
In this particular case and since this specific column is empty, you can also just omit \multirow{2}{*}{\textbf{}}
entirely.
Additionally to the two before mentioned solutions to getting rid of the error message, there are other issues with this table. Using resizebox
in order to make sure a table is as wide as the textwidth distorts the font sizes resulting in a bunch of different and inconsistent font sizes throughout your document. Since your table is narrow enough to not overflow into the margins, just omit the whole \resizebox
and you will end up with the following compilable example code:

\documentclass{article}
\begin{document}
\begin{table}[ht]
\centering
\begin{tabular}{|l|c|c|l|l|l|l|}
\hline
& \multicolumn{6}{c|}{\textbf{Metric}} \\ \cline{2-7}
& \multicolumn{3}{c|}{\textbf{SSIM}} & \multicolumn{3}{c|}{\textbf{IoU/F1}} \\ \hline
\textbf{Model} & \multicolumn{1}{l|}{\textbf{Max.}} & \multicolumn{1}{l|}{\textbf{Mean}} & \textbf{Min.} & \textbf{Max.} & \textbf{Mean} & \textbf{Min.} \\ \hline
\textbf{EfficientNetB7} & \textbf{0.956} & \textbf{0.877} & \textbf{0.761} & \textbf{0.988} & \textbf{0.952} & \textbf{0.897} \\ \hline
InceptionV3 & 0.944 & 0.863 & 0.758 & 0.977 & 0.947 & 0.894 \\ \hline
InceptionResNetV2 & 0.941 & 0.859 & 0.743 & 0.983 & 0.943 & 0.886 \\ \hline
DenseNet201 & 0.940 & 0.862 & 0.747 & 0.978 & 0.945 & 0.891 \\ \hline
\end{tabular}
\caption{Evaluation of the state-of-the-art models. EfficientNetB7 is proven to be the most suitable model with a high SSIM and IoU score.}
\label{tab:evaluation_models}
\end{table}
\end{document}
Personally, I would suggest to use a different approach omitting all vertical and most horizontal lines, replacing the few useful, horizontal lines with the ones from the booktabs
package for improved spacing and at the same time getting rid of the \textbf
commands. Highlighting all column headers does not really seem to make sense here. In order to align the numbers inside of their cells with respect to the decimal marker, I also used an S
column type from the siunitx
package. (For this particular table, a simple c
column would also work just as well). You can also combine this approach with tabular*
is you nevertheless want to make sure the table is as wide as the textwidth while not dirtorting font sizes:

\documentclass{article}
\usepackage{booktabs}
\usepackage{siunitx}
\begin{document}
\begin{table}[ht]
\caption{Evaluation of the state-of-the-art models. EfficientNetB7 is proven to be the most suitable model with a high SSIM and IoU score.}
\label{tab:evaluation_models}
\centering
\begin{tabular}{l*{6}{S[table-format=1.4]}}
\toprule
& \multicolumn{6}{c}{Metric} \\
\cmidrule{2-7}
& \multicolumn{3}{c}{SSIM} & \multicolumn{3}{c}{IoU/F1} \\
\cmidrule(r){2-4} \cmidrule(l){5-7}
Model & {Max.} & {Mean} & {Min.} & {Max.} & {Mean} & {Min.} \\
\midrule
EfficientNetB7 & 0.956 & 0.877 & 0.761 & 0.988 & 0.952 & 0.897 \\
InceptionV3 & 0.944 & 0.863 & 0.758 & 0.977 & 0.947 & 0.894 \\
InceptionResNetV2 & 0.941 & 0.859 & 0.743 & 0.983 & 0.943 & 0.886 \\
DenseNet201 & 0.940 & 0.862 & 0.747 & 0.978 & 0.945 & 0.891 \\
\bottomrule
\end{tabular}
\end{table}
\begin{table}[ht]
\caption{Evaluation of the state-of-the-art models. EfficientNetB7 is proven to be the most suitable model with a high SSIM and IoU score.}
\label{tab:evaluation_models}
\begin{tabular*}{\textwidth}{@{\extracolsep{\fill}}l*{6}{S[table-format=1.4]}}
\toprule
& \multicolumn{6}{c}{Metric} \\
\cmidrule{2-7}
& \multicolumn{3}{c}{SSIM} & \multicolumn{3}{c}{IoU/F1} \\
\cmidrule(r){2-4} \cmidrule(l){5-7}
Model & {Max.} & {Mean} & {Min.} & {Max.} & {Mean} & {Min.} \\
\midrule
EfficientNetB7 & 0.956 & 0.877 & 0.761 & 0.988 & 0.952 & 0.897 \\
InceptionV3 & 0.944 & 0.863 & 0.758 & 0.977 & 0.947 & 0.894 \\
InceptionResNetV2 & 0.941 & 0.859 & 0.743 & 0.983 & 0.943 & 0.886 \\
DenseNet201 & 0.940 & 0.862 & 0.747 & 0.978 & 0.945 & 0.891 \\
\bottomrule
\end{tabular*}
\end{table}
\end{document}
multirow
package in your preamble?\multirow
in this particular table? The upper left cell does not contain any text, so you could basically just omit\multirow{2}{*}{\textbf{}}
and get th eexact same output.\resizebox
on tables, it will produce inconsistent font sizes and rule widths compared with the rest of the document.resizebox
on a table as this will lead to inconsistent font sized throughout the document. Your table already fits into the available space without the need of resizing it. If you want to make sure, the table is as wide as the textwidth, you could usetabular*
instead.