# Distance between array rows

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

\documentclass{article}

\begin{document}

$$\left\{ \begin{array}{lll} C(\tau_{k,i})=0.5Q_e\ddot{q}_t^T\ddot{q}_t + 0.5R_e \theta^T \theta & when & t\neq t_v\\ \\ C(\tau_{k,i})=0.5Q_e\ddot{q}_t^T\ddot{q}_t + 0.5R_e \theta^T \theta + P_{viapoint} & when & t=t_v\\ \\ \quad\quad P_{viapoint}=10^{10}(q_{t}-q_{viapoint})^T(q_{t}-q_{viapoint}) \end{array}\right. \label{cost2}$$

\end{document}

which results in something like this:

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?

• Consider using the cases environment (part of the amsmath package) for this task. – John Wickerson Jul 19 '13 at 15:58
• Regarding the line spacing: I wonder if you've changed some setting earlier in your document, such as issuing \renewcommand\arraystretch{1.2}. Could you post a minimal working example please? – John Wickerson Jul 19 '13 at 16:01
• You have used \\ \\ so have a blank row between each row of text which is why the spacing is so bad. – David Carlisle Jul 19 '13 at 16:39

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