General ⇒ array justification

[CoolnessItself]

I'm trying to imitate a book I'm reading for spacing when formulating LP problems.
Try this guy:

Code: Select all

\[ \begin{array}{rlr}
    \mbox{minimize}  & \sum c_{ij}x_{ij} \\
    \mbox{subject to} & \sum\limits_{j=1}^{n}x_{ij} - \sum\limits_{k=1}^{n}x_{ki}   & i=1,2,...,n\\
                & x_{ij} \ge 0 &  i,j=1,2,...,n.
    \end{array}
\]

The two problems I can't figure out how to fix:
1) The n from the constraints (above summation in second line) looks like its supposed to be the index for the top-line summation, so line spacing between equations needs to be increased ... how?
2) Can the columns of the array be spaced out more, so that "minimize" is spaced farther left from the equations, and the listing of $i=1...n" is farther right? I think the right column especially should be spaced farther away from the text and equations. Greater spacing between columns would also be helpful.

Any ideas?

[php1ic]

You can alter the line spacing with \arraystretch, and for the columns I would suggest simply adding two more columns with nothing in them, as below.

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\renewcommand\arraystretch{2}
\[ \begin{array}{rclcr}

    \mbox{minimize}   && \sum c_{ij}x_{ij} \\
    \mbox{subject to} && \sum\limits_{j=1}^{n}x_{ij} - \sum\limits_{k=1}^{n}x_{ki}   && i=1,2,...,n\\
                      && x_{ij} \ge 0 && i,j=1,2,...,n.
    \end{array}
\]

If you only want to change the line spacing for this one set of equations, you can set it back to the default with \renewcommand\arraystretch{1}

[localghost]

It seems better to use amsmath and an environment provided by this package,

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\documentclass[11pt,a4paper,english]{article}
\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}
\usepackage{babel}
\usepackage{amsmath}

\begin{document}
  \begin{alignat*}{2}
    \text{minimize}\qquad & \sum c_{ij}x_{ij} \\
    \text{subject to}\qquad & \sum_{j=1}^{n}x_{ij}-\sum_{k=1}^{n}x_{ki}\qquad & i &= 1,2,\ldots,n \\
    & x_{ij} \ge 0 & i,j &= 1,2,\ldots,n.
  \end{alignat*}
\end{document}

The package manual tells you more.


Best regards
Thorsten