[Tex/LaTex] Distance between array rows

arraysequations

I am using the array environment to create a multiple row bracket expression, as folows:

\documentclass{article}

\begin{document}

\begin{equation}
\left\{ \begin{array}{lll}
C(\tau_{k,i})=0.5Q_e\ddot{q}_t^T\ddot{q}_t + 0.5R_e \theta^T \theta & when & t\neq t_v\\
\\
C(\tau_{k,i})=0.5Q_e\ddot{q}_t^T\ddot{q}_t + 0.5R_e \theta^T \theta +    P_{viapoint} & when & t=t_v\\
\\
\quad\quad P_{viapoint}=10^{10}(q_{t}-q_{viapoint})^T(q_{t}-q_{viapoint})

\end{array}\right.  
\label{cost2}
\end{equation}

\end{document}

which results in something like this:

enter image description here

However, the vertical spacing between the equations is much greater that the line spacing in the text, and is eating too much space on the paper. Is there a way to reduce the vertical spacing?

Best Answer

The array (and tabular) environment sets struts in rows. The size of the struts can be reduced by using smaller values than 1 or \arraystretch:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{equation}
\left\{
\renewcommand*{\arraystretch}{.5}
\begin{array}{lll}
C(\tau_{k,i})=0.5Q_e\ddot{q}_t^T\ddot{q}_t + 0.5R_e \theta^T \theta
& \text{when} &
t\neq t_v\\
\\
C(\tau_{k,i})=0.5Q_e\ddot{q}_t^T\ddot{q}_t + 0.5R_e \theta^T \theta +
P_{\text{viapoint}} & \text{when} & t=t_v\\
\\
\quad\quad P_{\text{viapoint}}
=10^{10}(q_{t}-q_{\text{viapoint}})^T(q_{t}-q_{\text{viapoint}})
\end{array}\right.
\end{equation}
\end{document}

You can also take a look at AmSLaTeX (package amsmath) that provides many environments for aligned/non-aligned equations and cases structures.

Related Solutions

[Tex/LaTex] aligning a multiline formula with the bullet of itemize

I would definitely go the second way with $\displaystyle: I find that it looks strange to have something centered after a bullet. To get the vertical alignment correct, just add [t] after \begin{aligned}, where "t" means "top". (See also the top of page 8 of the User's guide for the amsmath Package.)

[Tex/LaTex] cases and spacing between array rows

array increases the line spacing in a construct such as \\[2em] by adding 2em to its standard strut depth. However, your construction produces something that is deeper than the standard strut already, so the adjustment is not as much as you thought you requested. As you are using dcases which is in mathtools you could, or even should, use an align* environment instead, and that will space correctly.

Sample output

\documentclass{article}

\usepackage{mathtools}

\begin{document}

\verb+array+ example with large depth on lines has a problem:
\[
\begin{array}{l}
  f(x) = \vrule height 2em depth 2em \\[2em]
  g(x) = x \\[2em]
  k(x) = \vrule height 2em depth 2em
\end{array}
\]

The \verb+align*+ version of the original code spaces correctly.

\begin{align*}
  f(x) &=%
  \begin{dcases}
    -1 & x < 0 \\
    1 & x > 0
  \end{dcases} \\[2em]
  g(x) &= x \\[2em]
  k(x) &=%
  \begin{dcases}
    -1 & x < 0 \\
    1 & x > 0
  \end{dcases}
\end{align*}
\end{document}

Best Answer

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[Tex/LaTex] cases and spacing between array rows

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