1

i want to increase space between rows of this vector\overrightarrow{grad}, in the equation below:

\begin{eqnarray}
 \nonumber \vec F=\vec P=\left(
 \begin{array}{ccc}
  0\\0\\ _mg
 \end{array}
\right)_{(\vec i, \vec j, \vec k)} \hspace{0.2cm}\textrm{ et }\hspace{0.2cm}
\overrightarrow{grad}V(\sum)=\left(
\begin{array}{ccc}
 \left.\frac{\partial V_x(\sum) }{\partial x}\right.\\ \left.\frac{\partial V_y(\sum) }{\partial y}\right.\\ \left.\frac{\partial V_z(\sum) }{\partial z}\right.
\end{array}
\right)_{(\vec i, \vec j, \vec k)}
\end{eqnarray}
  • 1
    Do not use eqnarray. It gives bad horizontal spacing around the alignment points (which you have not here, anyway). This being said, you can add to your preamble, say \setlength{\extrarowheight}{2pt}. – Bernard Apr 14 '18 at 22:43
  • thank you, i find reply to my question, in this answer answer – moradov Apr 14 '18 at 22:43
  • 1
    If it is for a too high content touching the above and/or below row, the best solution, in my opinion, consists in using the cellspace package. – Bernard Apr 14 '18 at 22:47
  • thank you @Bernard, i used {\setstretch{1.75} \begin{alignat*}{2} ........ \end{alignat*}} by including the setspace package, it work well for me. – moradov Apr 14 '18 at 22:56
  • 1
    It's another possible solution. Take care of the spacing on entering and leaving the environment, however. – Bernard Apr 14 '18 at 22:58
1

You should never use eqnarray, even less for a single equation.

Also there are some strange things in your input, for instance \left. and \right. that only add (unwanted) spaces and \sum for what should probably be \Sigma.

Better use pmatrix instead of array; I also defined a shorthand for partial derivatives.

For the “touching” fractions, add some vertical space as shown.

\documentclass{article}
\usepackage{amsmath}

\newcommand{\pder}[2]{\frac{\partial #1}{\partial #2}}
\DeclareMathOperator{\grad}{\overrightarrow{\mathrm{grad}}}

\begin{document}

\begin{equation*}
\vec{F}=\vec{P}=
\begin{pmatrix}
0 \\ 0 \\ {}_mg
\end{pmatrix}_{(\vec{i}, \vec{j}, \vec{k})}
\quad\text{et}\quad
\grad V(\Sigma)=
\begin{pmatrix}
\pder{V_x(\Sigma)}{x} \\[1ex]
\pder{V_y(\Sigma)}{y} \\[1ex]
\pder{V_z(\Sigma)}{z}
\end{pmatrix}_{(\vec{i}, \vec{j}, \vec{k})}
\end{equation*}

\end{document}

enter image description here

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