missing $ inserted (in a table)

Question

I am using this code to generate a table in the document. It keeps giving me the error, Missing $ inserted. I am unable to figure out this error.

\begin{table}[htbp]
  \centering
    \begin{tabular}{lrrrrr}
          & \multicolumn{5}{c}{DeCLUTR Base} \\
    Pairs & \multicolumn{1}{l}{\omega_c^1} & \multicolumn{1}{l}{\omega_c^2} & \multicolumn{1}{l}{\Omega_c} & \multicolumn{1}{l}{z_{s,t}} & \multicolumn{1}{l}{$Q$} \\
    A1 - A2 & 0.24  & 0.55  & 0.40  & 0.83  & 2.09 \\
    A1 - A3 & 0.26  & 0.51  & 0.39  & 0.83  & 2.15 \\
    A2 - A3 & 0.39  & 0.33  & 0.36  & 0.84  & 2.31 \\
          &       &       &       &       &  \\
    I1 - I2 & 0.33  & 0.41  & 0.37  & 0.83  & 2.24 \\
    I1 - I3 & 0.25  & 0.49  & 0.37  & 0.82  & 2.22 \\
    I1 - I4 & 0.58  & 0.24  & 0.41  & 0.83  & 2.04 \\
    I2 - I3 & 0.29  & 0.47  & 0.38  & 0.83  & 2.20 \\
    I2 - I4 & 0.65  & 0.23  & 0.44  & 0.83  & 1.90 \\
    I3 - I4 & 0.76  & 0.16  & 0.46  & 0.82  & 1.80 \\
          &       &       &       &       &  \\
    O1 - O2 & 0.25  & 0.48  & 0.37  & 0.83  & 2.25 \\
    O1 - O3 & 0.61  & 0.21  & 0.41  & 0.83  & 2.00 \\
    O1 - O4 & 0.42  & 0.34  & 0.38  & 0.83  & 2.21 \\
    O2 - O3 & 0.81  & 0.15  & 0.48  & 0.82  & 1.72 \\
    O2 - O4 & 0.55  & 0.23  & 0.39  & 0.83  & 2.13 \\
    O3 - O4 & 0.24  & 0.55  & 0.40  & 0.84  & 2.12 \\
          &       &       &       &       &  \\
    M1 - M2 & 0.34  & 0.35  & 0.34  & 0.84  & 2.43 \\
    \end{tabular}
  \label{Tab:warp_coeff_declutr_b}
  \caption{Warp coefficients for DeCLUTR Base}
\end{table}%

Here is the errror.

Answer 1

As David Carlisle has already pointed out in a comment, math-y expressions such as \omega_c^1, \omega_c^2, \Omega_c, and z_{s,t} must be rendered in math mode -- inline math mode, to be precise.

I would further like to suggest that you align the numbers explicitly on their decimal markers, say by loading the siunitx package and employing its S column type. (For the table at hand, it actually makes no difference whether you use the l, c, r, or S column type.)

Oh, and do take care to place the \caption directive before, not after, the \label directive. This matters greatly if you ever intend to cross-reference this table via LaTeX's \label-\ref mechanism.

\documentclass{article} % or some other suitable document class
\usepackage{booktabs} % for \toprule, \cmidrule, \midrule, \addlinespace, and \bottomrule macros 
\usepackage{siunitx}  % for the 'S' column type

\begin{document}
\begin{table}[htbp]
  \centering
  \begin{tabular}{@{} l *{5}{S[table-format=1.2]} @{}}
    \toprule
    Pairs & \multicolumn{5}{c@{}}{DeCLUTR Base} \\
    \cmidrule(l){2-6}
    & {$\omega_c^1$} & {$\omega_c^2$} & {$\Omega_c$} & {$z_{s,t}$} & {$Q$} \\
    \midrule
    A1--A2 & 0.24  & 0.55  & 0.40  & 0.83  & 2.09 \\
    A1--A3 & 0.26  & 0.51  & 0.39  & 0.83  & 2.15 \\
    A2--A3 & 0.39  & 0.33  & 0.36  & 0.84  & 2.31 \\ \addlinespace
    I1--I2 & 0.33  & 0.41  & 0.37  & 0.83  & 2.24 \\
    I1--I3 & 0.25  & 0.49  & 0.37  & 0.82  & 2.22 \\
    I1--I4 & 0.58  & 0.24  & 0.41  & 0.83  & 2.04 \\
    I2--I3 & 0.29  & 0.47  & 0.38  & 0.83  & 2.20 \\
    I2--I4 & 0.65  & 0.23  & 0.44  & 0.83  & 1.90 \\
    I3--I4 & 0.76  & 0.16  & 0.46  & 0.82  & 1.80 \\ \addlinespace
    O1--O2 & 0.25  & 0.48  & 0.37  & 0.83  & 2.25 \\
    O1--O3 & 0.61  & 0.21  & 0.41  & 0.83  & 2.00 \\
    O1--O4 & 0.42  & 0.34  & 0.38  & 0.83  & 2.21 \\
    O2--O3 & 0.81  & 0.15  & 0.48  & 0.82  & 1.72 \\
    O2--O4 & 0.55  & 0.23  & 0.39  & 0.83  & 2.13 \\
    O3--O4 & 0.24  & 0.55  & 0.40  & 0.84  & 2.12 \\ \addlinespace
    M1--M2 & 0.34  & 0.35  & 0.34  & 0.84  & 2.43 \\
    \bottomrule
  \end{tabular}
  \caption{Warp coefficients for DeCLUTR Base}
  \label{Tab:warp_coeff_declutr_b}
\end{table}

\end{document}

Answer 2

A small variation of nice @mico answer: with use of the tabularray package:

\documentclass{article} 
\usepackage{tabularray}
\UseTblrLibrary{booktabs,siunitx}  

\begin{document}
\begin{table}[htbp]
\centering
    \begin{tblr}{colspec={c *{5}{Q[c,si={table-format=1.2},$]}} }
    \toprule
\SetCell[r=2]{c}    Pairs 
        & \SetCell[c=5]{c, mode=text} {{{DeCLUTR Base}}}
                &       &       &       &       \\
    \cmidrule[l]{2-6}
        & {{{\omega_c^1}}}
                & {{{\omega_c^2}}}
                        & {{{\Omega_c}}}
                                & {{{z_{s,t}}}}
                                        & {{{Q}}} \\
    \midrule
A1--A2  & 0.24  & 0.55  & 0.40  & 0.83  & 2.09 \\
A1--A3  & 0.26  & 0.51  & 0.39  & 0.83  & 2.15 \\
A2--A3  & 0.39  & 0.33  & 0.36  & 0.84  & 2.31 \\ 
    \addlinespace
I1--I2  & 0.33  & 0.41  & 0.37  & 0.83  & 2.24 \\
I1--I3  & 0.25  & 0.49  & 0.37  & 0.82  & 2.22 \\
I1--I4  & 0.58  & 0.24  & 0.41  & 0.83  & 2.04 \\
I2--I3  & 0.29  & 0.47  & 0.38  & 0.83  & 2.20 \\
I2--I4  & 0.65  & 0.23  & 0.44  & 0.83  & 1.90 \\
I3--I4  & 0.76  & 0.16  & 0.46  & 0.82  & 1.80 \\ 
    \addlinespace
O1--O2  & 0.25  & 0.48  & 0.37  & 0.83  & 2.25 \\
O1--O3  & 0.61  & 0.21  & 0.41  & 0.83  & 2.00 \\
O1--O4  & 0.42  & 0.34  & 0.38  & 0.83  & 2.21 \\
O2--O3  & 0.81  & 0.15  & 0.48  & 0.82  & 1.72 \\
O2--O4  & 0.55  & 0.23  & 0.39  & 0.83  & 2.13 \\
O3--O4  & 0.24  & 0.55  & 0.40  & 0.84  & 2.12 \\ 
    \addlinespace
M1--M2  & 0.34  & 0.35  & 0.34  & 0.84  & 2.43 \\
    \bottomrule
\end{tblr}
    \caption{Warp coefficients for DeCLUTR Base}
    \label{Tab:warp_coeff_declutr_b}
\end{table}

\end{document}

In comparison to "clasic" table's packages the tabularray has a bit different syntax multcolumn and multirow determine \SetCell, for cells and columns define modes math, dmath and text etc. For details see package documentations.

Result of above MWE is the same as is in @Mico answer: