# Extra alignment tab has been changed to \cr. \end{multline}

How do I represent this matrix sum in two lines? I am getting the error "Extra alignment tab has been changed to \cr. \end{multline}"

\begin{multline}
\begin{bmatrix}
\dot{i_v} \\ \dot{i_o} \\ \dot{V_o}
\end{bmatrix} =
\begin{bmatrix}
\frac{-R_f}{L_f} & 0 &\frac{1}{L_f}\\ 0 & \frac{-R_o}{L_o} & \frac{-1}{L_o} \\ \frac{1}{C_f} & \frac{-1}{C_f} & 0
\end{bmatrix}
\begin{bmatrix}
\Delta{i_v} \\ \Delta{i_o} \\ \Delta{V_o}
\end{bmatrix} +
\begin{bmatrix}
\frac{1}{L_f} \\ 0 \\ 0
\end{bmatrix}
\begin{bmatrix}
\Delta{V_t}
\end{bmatrix}
& + \begin{bmatrix}
0 \\ \frac{-1}{L_o} \\ 0
\end{bmatrix}
\begin{bmatrix}
\Delta{V_{dc}}
\end{bmatrix}
\end{multline}

• Your last & is outside the bmatrix but i side the multline. Wrongly placed. Jun 30, 2022 at 5:36
• Yes that is where i want to break the matrice sum onto next line.
– Dan
Jun 30, 2022 at 6:15
• Multline does not support alignments, so that & which mickep mentions is an error in multline. Use \\ to break the line, or switch to align instead. Jun 30, 2022 at 7:05

\end{bmatrix}
& + \begin{bmatrix}


This & is outside the matrices and thus is interpreted by multline. But multline does not support alignments and thus & gives an error here.

You mention in a comment that this is the location where you want a line break. Then replace this & by \\ and you get what you wanted:

\documentclass[a4paper]{article}
\usepackage{amsmath}
\begin{document}
\begin{multline}
\begin{bmatrix}
\dot{i_v} \\ \dot{i_o} \\ \dot{V_o}
\end{bmatrix} =
\begin{bmatrix}
\frac{-R_f}{L_f} & 0 &\frac{1}{L_f}\\ 0 & \frac{-R_o}{L_o} & \frac{-1}{L_o} \\ \frac{1}{C_f} & \frac{-1}{C_f} & 0
\end{bmatrix}
\begin{bmatrix}
\Delta{i_v} \\ \Delta{i_o} \\ \Delta{V_o}
\end{bmatrix} +
\begin{bmatrix}
\frac{1}{L_f} \\ 0 \\ 0
\end{bmatrix}
\begin{bmatrix}
\Delta{V_t}
\end{bmatrix}
\\
+ \begin{bmatrix}
0 \\ \frac{-1}{L_o} \\ 0
\end{bmatrix}
\begin{bmatrix}
\Delta{V_{dc}}
\end{bmatrix}
\end{multline}
\end{document}