6

I'm trying to typeset the matrix depicted in the diagram, I've considered many examples, and in particular easybmat. But nothing came closer than the approach I settled on given below. However it does not quite produce the accuracy I wanted. Is there a way to make the diagram closer to the required picture?

Matrix design

This is my code:

\documentclass{article}
\usepackage{amsmath}
\usepackage{multirow}
\usepackage{easybmat}

\begin{document}

\[
\sbox0{$\begin{array}{c |}a_1\\ \hline\end{array}$}
\sbox1{$\begin{array}{c c |}b_1&b_2\\ \hline\end{array}$}
\sbox2{$\begin{array}{c c c |}c_1& \  c_2&c_3\\ \hline\end{array}$}
\sbox3{$\begin{array}{c c c c |}...&...&... &...\\ \hline\end{array}$}
\sbox4{$\begin{array}{c c c c c |}...&...&...&...&...\\ \hline\end{array}$}
\sbox5{$\begin{array}{c c c c c c |}\alpha_n &\beta_n&\gamma_n&\epsilon_n&\delta_n& ...............\\ \hline\end{array}$}
%
A=\left(
\begin{array}{c c c c c c c }
\usebox{0} \ a_2 \ \ \ a_3 \ \ a_4 \ a_5 \ ... \ ... \ ... \ ... \ ... \ a_n\\
\usebox{1} \ b_3 \ \ b_4 \ b_5 \ ... \ ... \ ... \ ... \ ... \ b_n\\
\usebox{2} \ c_4 \ c_5 \ ... \ ... \ ... \ ... \ ..\ c_n\\
\usebox{3} \ ... \ ... \ ... \ ... \ ... \ ... \ ... \\
\usebox{4} \ ... \ ... \ ... \ ... \ ... \\
\usebox{5} \\
\end{array}
\right)
\]

\end{document}
  • Possible duplicate of Latex typesetting – Henri Menke Jun 24 '17 at 5:39
  • 1
    Welcome to TeX SX! Just a question aside: shouldn't P_n be P_{n-1} really? – Bernard Jun 24 '17 at 9:20
10

You could also use a tikz matrix:

\documentclass{article}
\usepackage{amsmath,tikz}
\usetikzlibrary{matrix, positioning}

\begin{document}
    \begin{equation}
    A=\begin{tikzpicture}[baseline=-.8ex] 
    \matrix[%
    matrix of math nodes,
    nodes in empty cells,
    column 6/.style={nodes={text width=1.2em}},
    nodes={minimum height=4ex, text width=1.5em, align=center, inner sep=4pt},
    left delimiter={(},right delimiter={)}, 
    inner xsep=-1pt, column sep=0pt, 
    ] (m)
    {%
        a_1 & a_2 & a_3 & a_4 & \dots &[2pt] a_n \\
        b_1 & b_2 & b_3 & b_4 & \dots & b_n \\
        c_1 & c_2 & c_3 & c_4 & \dots & c_n \\
        \dots & \dots & \dots & \dots & \dots & \dots \\
        \alpha_{n} &\beta_{n}&\gamma_{n}&\delta_{n}& \dots & \mu_{n} \\
    };
    \foreach \n in {1,...,3}{%
        \draw [->] (m-\n-1.south west) -- (m-\n-\n.south east) -- (m-1-\n.north east)  node[above]{$P_{\n}$};
    }
    \draw [->] (m-4-1.south west) -- (m-4-5.south east) -- (m-1-5.north east)  node[above]{$P_{n}$};
    \end{tikzpicture}
    \end{equation}
\end{document}

enter image description here

7

You can use the tikzmark library to mark the points at line joints and later draw these lines using normal tikz paths

\documentclass{article}
\usepackage{amsmath,tikz}
\usetikzlibrary{tikzmark}

\begin{document} 

\[
A=\left(
\begin{array}{*7c}
 \tikzmark{11}\,a_2\,\tikzmark{12}  & a_3  & a_4  & a_5 & \dots & \dots& a_n\\
 \tikzmark{21}\,b_3  & \,b_4\,\tikzmark{22}  & b_5  & \dots& \dots& \dots& b_n\\
 \tikzmark{31}\,c_4  & c_5  & \dots\tikzmark{32}& \dots& \dots& \dots& c_n\\
 \tikzmark{41}\dots& \dots& \dots& \dots\tikzmark{42}& \dots& \dots& \dots\\
 \tikzmark{51}\dots& \dots& \dots& \dots& \dots\tikzmark{52}& \dots& \dots \\
\end{array}
\right)
\]

\begin{tikzpicture}[remember picture, overlay]
\foreach \n in {1,...,5}
\draw [->] ([yshift=-3pt]pic cs:\n1) -- ([yshift=-3pt]pic cs:\n2) --++(0,\n\baselineskip)node[above]{$p_\n$};
\end{tikzpicture}

\end{document}

enter image description here

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