Math & Science ⇒ Highlighting in matrices

[salehin]

Can you please let me know how to highlight (using any soft colour) the main diagonal of this square matrix.

Thank you for reading.

Code: Select all

\documentclass[a4paper]{article}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{graphicx}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amstext}
\usepackage{hyperref}
\hypersetup{colorlinks=true, linkcolor=blue}
\begin{document}
 
\begin{equation*}
    \left[
\begin{array}{cccc}
\sigma _{1}^{2} & \sigma _{12} & \cdots  & \sigma _{1k} \\
\sigma _{21} & \sigma _{2}^{2} & \cdots  & \sigma _{2k} \\
\vdots  & \vdots  & \ddots  & \vdots  \\
\sigma _{k1} & \sigma _{k2} & \cdots  & \sigma _{k}^{2}%
\end{array}
    \right] 
=\Omega
\end{equation*}

\end{document} 

[gmedina]

Hi,

you could try using \cellcolor from the colortbl package, loaded via xcolor:

Code: Select all

\documentclass[a4paper]{article}
\usepackage{amsmath}
\usepackage[table]{xcolor}

\begin{document}

\begin{equation*}
  \left[
  \begin{array}{cccc}
    \cellcolor{blue!20}\sigma _{1}^{2} & \sigma _{12} & \cdots  & \sigma _{1k} \\
    \sigma _{21} & \cellcolor{blue!20}\sigma _{2}^{2} & \cdots  & \sigma _{2k} \\
    \vdots  & \vdots  & \ddots  & \vdots  \\
    \sigma _{k1} & \sigma _{k2} & \cdots  & \cellcolor{blue!20}\sigma _{k}^{2}%
  \end{array}
  \right] 
  =\Omega
\end{equation*}

\end{document}

[salehin]

Thanks for your help, gmedina. It should do the job for me.

Regards

Saleh

[tonyjnel]

That's really great gmedina, and I know i'm being nit-picky at this point, but is there a way that the highlighted cells can be highlighted by a triangle rather than the stair-step shape generated by this code. It may only make sense physically to do this with matrices that only have single character entries but can it be done?

Thanks,
Tony