# array environment: missing $inserted and some other issues I have the following code: \begin{array}{cc|c|c|} & & \multicolumn{2}{c}{odd} \\ & & 0 & 1 \\ \cline{3-4} \multirow{2}{*}{even} & 0 &$(+1,-1)$&$(-1,+1)$\\ \cline{3-4} & 1 &$(-1,+1)$&$(+1,-1)$\\ \cline{3-4} \end{array}  It gives me a "missing$ inserted" error, and produces the following table:

As you might see, there are two issues:

1. Some of the cells are in math environment and some aren't, and it's almost the opposite of my intentions. I get that it has something to do with the error, but I can't see what's the problem or how to fix it - I simply put $...$ inside a cell that should be in math mode! Just to make it clear, I want the titles "odd", "even", "0", "1" to be regular text, and the vectors to be in math mode.
2. I don't know how to get rid of the upper parts of the three vertical lines. I want them to only strech across the two bottom cells, symmetrically to the horizontal lines.

I'd appriciate to hear your suggestions.

• The array environment must occur in math mode. In your example, LaTeX encounters the instruction \begin{array}{cc|c|c|} in text mode and hence issues a complaint. – Mico May 6 at 17:17

Here are two different versions using either an array or a tabular environment:

\documentclass{article}
\usepackage{amsmath}
\usepackage{multirow}
\begin{document}
$\begin{array}{cc|c|c|} \multicolumn{2}{c}{} & \multicolumn{2}{c}{\text{odd}} \\ \multicolumn{2}{c}{} & \multicolumn{1}{c}{0} & \multicolumn{1}{c}{1} \\ \cline{3-4} \multirow{2}{*}{\text{even}} & 0 & (+1,-1) & (-1,+1) \\ \cline{3-4} & 1 & (-1,+1) & (+1,-1) \\ \cline{3-4} \end{array}$

\begin{tabular}{cccc}
&  & \multicolumn{2}{c}{odd} \\
& & 0 & 1 \\
\cline{3-4}
\multirow{2}{*}{even} & 0 &  \multicolumn{1}{|c|}{$$(+1,-1)$$} & \multicolumn{1}{c|}{$$(-1,+1)$$} \\
\cline{3-4}
& 1 & \multicolumn{1}{|c|}{$$(-1,+1)$$} & \multicolumn{1}{c|}{ $$(+1,-1)$$} \\
\cline{3-4}
\end{tabular}

\end{document}

• array based approach: Place the whole array in math mode (via $ and $) and use \text from amsmath for the texts.

• tabular based appoach: Just place the contents of each cell into math mode (via $$ and $$).

• globally defined vertical lines: Use \multicolumn{1}{c}{} to remove the vertical lines where you don't want them

• locally added verticcal lines: Define your table without vertical lines and use \multicolumn{1}{|c|}{...} or \multicolumn{1}{c|}{...} to add them whenever needed.

• +1. You might want to replace \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & with \multicolumn{2}{c}{} &, though. – Mico May 6 at 17:24