Missing $ inserted inside matrix

Question

I'm getting "missing $ inserted" (along with a lot of other nearby errors, but that's the first one) on this snippet:

$$
(\tilde A-\lambda)^m =
\begin{blockarray}{(cccc)}
        \BAmulticolumn{3}{c}{\multirow{3}{*}{(A-\lambda)^m}} & \multirow{3}{*}{\vdots} \\
        & & & & \\ \\
        0 & \dots & 0 & (1-\lambda)^m
\end{blockarray}
\end{pmatrix}
$$

Specifically, it's at the line

\BAmulticolumn{3}{c}{\multirow{3}{*}{(A-\lambda)^m}} & \multirow{3}{*}{\vdots}

I can't find a way to see exactly where the $ was inserted, but either way I have no idea why there would be one there. The code renders fine, the error is just bothering me.

Hello! What is blockarray? And where is pmatrix started? And heck, could you please provide a minimal working example (MWE)? — yo', Oct 07 '14 at 17:04
You need to inform us of what \BAmulticolumn looks like. In fact, instead of providing us with only a code snippet, show a minimal working example (MWE). — Werner, Oct 07 '14 at 17:04
The \end{pmatrix} was a typo, removing it hasn't changed the issue, though. I actually couldn't provide a MWE because I really have no idea what I'm doing - I copy pasted this snippet and modified it using my limited knowledge of TeX until it (mostly) worked. — Jack M, Oct 07 '14 at 17:07

score 4 · Answer 1 · answered Oct 07 '14 at 17:50

4

You need neither multirow nor blkarray:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\[
(\tilde A-\lambda)^m =
\begin{pmatrix}
(A-\lambda)^m & \vdots\vphantom{\Bigg|} \\
\begin{matrix}0 & \dots & 0\end{matrix} & (1-\lambda)^m
\end{pmatrix}
\]

\end{document}

enter image description here

answered Oct 07 '14 at 17:50

egreg

1,121,712

why not just 0 \quad\dots\quad 0 for the first part of the second line, and why is the extra height needed with the \Bigg|? adding an optional space [2\jot] (or even a bit more) would put the extra space only between the lines where it's really wanted. (or am i missing something?) – barbara beeton Oct 07 '14 at 20:38
@barbarabeeton I wanted to reproduce the same spacing made by pmatrix, so a nested matrix seems best. The space above (A-\lambda)^m is probably meant for making clear that it's a submatrix, rather than a row. – egreg Oct 07 '14 at 20:43

score 3 · Accepted Answer · edited Jun 10 '20 at 12:32

3

You were missing the $ in the \multirow and had an extraneous \end{pmatrix}:

enter image description here

Notes:

I replaced the $$...$$ with \[ ... \]. As Werner pointed out, please see Why is \[ ... \] preferable to $$ ... $$?.
The $ were required in the option to \multirow as that parameter is assumed to be in text mode. Using the $ ensures that math mode is used.

Code:

\documentclass{article}
\usepackage{amsmath}
\usepackage{blkarray}
\usepackage{multirow}
\begin{document}
[
(\tilde A-\lambda)^m =
\begin{blockarray}{(cccc)}
        \BAmulticolumn{3}{c}{\multirow{3}{}{$(A-\lambda)^m$}} & \multirow{3}{}{\vdots} \
        & & & & \ \
        0 & \dots & 0 & (1-\lambda)^m
\end{blockarray}
%\end{pmatrix}
]
\end{document}

edited Jun 10 '20 at 12:32

Community

1

answered Oct 07 '14 at 17:09

Peter Grill

223,288

Could you explain why $s are needed in the \multirow? Does the \begin{blockmatrix} break out of math mode? – Jack M Oct 07 '14 at 17:14
@JackM: Added brief explanation. – Peter Grill Oct 07 '14 at 17:21
A simple pmatrix will produce the same result.The blkarray environment is designed for block matrices. – Bernard Oct 07 '14 at 17:45

Missing $ inserted inside matrix

2 Answers2

Notes:

Code: