# Breaking long equation after a certain left bracket

I am typing a long equation which needs to be broken just after the left bracket and three dots are placed at the end of the left bracket same line. Here is an example, in which, I need the third left bracket (i.e. of the column vector just before the plus sign) to be followed by three dots while aligning the rest of the equation in the newline with the equal sign.

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{center}
$$\left[ \begin{array}{c} \dot{\omega}_m \\ \dot{\theta}_m \\ \dot{\omega}_v \\ \dot{I}_m \\ \end{array} \right] = \left[ \begin{array}{cccc} -\frac{C_m}{J_m} & -\frac{P_s K_s \psi}{2 \pi r_s^2 J_m} & 0 & \frac{K_{tm}}{J_m} \\ 1 & 0 & 0 & 0 \\ 0 & -\frac{P_s K_s \mu_p R_{mp}}{2 \pi r_s J_v} & -\frac{C_v}{J_v} & 0 \\ -\frac{K_{em}}{L_m} & 0 & 0 & -\frac{R_m}{L_m} \\ \end{array} \right] \left[ \begin{array}{c} \omega_m \\ \theta_m \\ \omega_v \\ I_m \\ \end{array} \right] + \left[ \begin{array}{cc} 0 & 0 \\ 0 & 0 \\ \frac{1}{J_v} & 0 \\ 0 & \frac{1}{L_m} \\ \end{array} \right] \left[ \begin{array}{c} F_v \\ V_m(t) \\ \end{array} \right]$$
\end{center}

\end{document}


-
It's rather difficult to understand what you want, as there's no line break. – egreg Apr 15 '12 at 19:35
After the equal sign, there is a left bracket which I need the break occurs after and three dots are placed to indicate a line break. – Diaa Abidou Apr 15 '12 at 19:42
Sorry, but one has to know better the context: are you using an aligning display math environment? – egreg Apr 15 '12 at 19:43

It's not at all clear what you want to do; I would split the equation in this way

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{aligned} \begin{bmatrix} \dot{\omega}_m \\ \dot{\theta}_m \\ \dot{\omega}_v \\ \dot{I}_m \\ \end{bmatrix} &= \begin{bmatrix} -\frac{C_m}{J_m} & -\frac{P_s K_s \psi}{2 \pi r_s^2 J_m} & 0 & \frac{K_{tm}}{J_m} \\ 1 & 0 & 0 & 0 \\ 0 & -\frac{P_s K_s \mu_p R_{mp}}{2 \pi r_s J_v} & -\frac{C_v}{J_v} & 0 \\ -\frac{K_{em}}{L_m} & 0 & 0 & -\frac{R_m}{L_m} \\ \end{bmatrix} \begin{bmatrix} \omega_m \\ \theta_m \\ \omega_v \\ I_m \\ \end{bmatrix} \\ &\qquad+ \begin{bmatrix} 0 & 0 \\ 0 & 0 \\ \frac{1}{J_v} & 0 \\ 0 & \frac{1}{L_m} \\ \end{bmatrix} \begin{bmatrix} F_v \\ V_m(t) \\ \end{bmatrix} \end{aligned}

\end{document}


The center environment is out of place; the bmatrix environment gives better matrices than \left[\begin{array}{..}...\end{array}\right].

With a reduced column width one can try and squeeze the matrix columns and break at the product. Here's an example at a column width of 229.5pt (3.2 inches or 8 centimeters):

\documentclass[twocolumn]{article}
\usepackage{amsmath}
\begin{document}
\pagestyle{empty}

\setlength{\arraycolsep}{1pt} \begin{aligned} \begin{bmatrix} \dot{\omega}_m \\ \dot{\theta}_m \\ \dot{\omega}_v \\ \dot{I}_m \\ \end{bmatrix} &= \begin{bmatrix} -\frac{C_m}{J_m} & -\frac{P_s K_s \psi}{2 \pi r_s^2 J_m} & 0 & \frac{K_{tm}}{J_m} \\ 1 & 0 & 0 & 0 \\ 0 & -\frac{P_s K_s \mu_p R_{mp}}{2 \pi r_s J_v} & -\frac{C_v}{J_v} & 0 \\ -\frac{K_{em}}{L_m} & 0 & 0 & -\frac{R_m}{L_m} \\ \end{bmatrix} \\ &\qquad\cdot \begin{bmatrix} \omega_m \\ \theta_m \\ \omega_v \\ I_m \\ \end{bmatrix} + \begin{bmatrix} 0 & 0 \\ 0 & 0 \\ \frac{1}{J_v} & 0 \\ 0 & \frac{1}{L_m} \\ \end{bmatrix} \begin{bmatrix} F_v \\ V_m(t) \\ \end{bmatrix} \end{aligned}
\end{document}


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Sorry for not being clear and grateful for your help. how about making the break just after the left bracket of the rightmost column vector in your answer preview ? – Diaa Abidou Apr 15 '12 at 20:41
@Diaa But do you really want to split after a left bracket? – egreg Apr 15 '12 at 20:43
Yes, that's what I am talking about, since I want to type this equation in two-column article format and I don't know where to break the equation to fit the desired format. – Diaa Abidou Apr 15 '12 at 20:46
Can you tell the column width? Breaking after a left bracket would be the very last resort. – egreg Apr 15 '12 at 20:50
From Elsevier guide, it states the width will be 224pt in the two-columns format – Diaa Abidou Apr 15 '12 at 20:56

It wasn't very clear exactly what alignment you meant, but for any kind of math alignment it is usually best to use the amsmath package. I think you meant this:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\newcommand\arrayb{
\begin{array}{c}
\omega_m \\
\theta_m \\
\omega_v \\
I_m
\end{array}}

\begin{align}
\left[
\begin{array}{c}
\dot{\omega}_m \\
\dot{\theta}_m \\
\dot{\omega}_v \\
\dot{I}_m
\end{array}
\right]
&=
\left[
\begin{array}{cccc}
-\frac{C_m}{J_m} & -\frac{P_s K_s \psi}{2 \pi r_s^2 J_m} & 0 & \frac{K_{tm}}{J_m} \\
1 & 0 & 0 & 0 \\
0 & -\frac{P_s K_s \mu_p R_{mp}}{2 \pi r_s J_v} & -\frac{C_v}{J_v} & 0 \\
-\frac{K_{em}}{L_m} & 0 & 0 & -\frac{R_m}{L_m}
\end{array}
\right]
\left[\vphantom{\arrayb}\right.\cdots
\\\notag
&
\left.\arrayb\right]
+
\left[
\begin{array}{cc}
0 & 0 \\
0 & 0 \\
\frac{1}{J_v} & 0 \\
0 & \frac{1}{L_m}
\end{array}
\right]
\left[
\begin{array}{c}
F_v \\
V_m(t)
\end{array}
\right]
\end{align}

\end{document}

-
This works perfectly, but when I tried to apply this for my equation an error was generated saying wrong nesting of equation structure. So, I dont know what to do. Kindly, could you tell me whether to paste my original equation in the comment or edit my original post ? – Diaa Abidou Apr 15 '12 at 20:06
Sorry for my confusion, but do you mean that I edit my original post ? – Diaa Abidou Apr 15 '12 at 20:18
I am really grateful for your patience. I've edited the question to my original equation. – Diaa Abidou Apr 15 '12 at 20:29
I deleted some of the earlier comments as no longer relevant (you may do same:-) and updated the answer based on your new example – David Carlisle Apr 15 '12 at 20:45