# Support Function Notation

How can I write an equation having the following term in LaTeX:

The hard part for me is to align the W in the right hand side.

• ?The W should be aligned in which way, exactly? – Bernard Jun 22 '18 at 21:06
• @Bernard It should be on the same baseline as -\delta^*. – Heiko Oberdiek Jun 22 '18 at 21:23

You can have both a friendly syntax and varying size for inline and displayed formulas.

\documentclass{article}
\usepackage{amsmath,mleftright}

\makeatletter
\newcommand{\support}[1]{\aslv@support#1\@nil}
\def\aslv@support#1\\#2|#3\@nil{%
\mleft(
\genfrac..{0pt}{}{#1}{#2}
\mskip\aslv@supportskip
\middle|
\mskip\aslv@supportskip
#3
\mright)
}
\newmuskip\aslv@supportskip
\aslv@supportskip=4mu % <--- adjust to suit
\makeatother

\begin{document}

We have the formula in line $\delta^+\support{1+d^Tr \\ V^Td+b(x) | W}$
or displayed
$\delta^+\support{1+d^Tr \\ V^Td+b(x) | W}$

\end{document}


• A quite elegant code! – Bernard Jun 23 '18 at 8:35

There are a number of ways to achieve this. I list two below, the first using a pmatrix (from amsmath) and the other using regular \left/\right extensible parentheses (you can also use \mleft/\mright from mleftright):

\documentclass{article}

\usepackage{amsmath,mleftright}

\begin{document}

% Uses amsmath
$a \begin{pmatrix} \begin{array}{@{} c | @{\hspace{\arraycolsep}}} b \\ c \end{array} d \end{pmatrix}$

% Uses mleftright, but can also just use \left/\right instead of \mleft/\mright
$a \mleft( \begin{array}{@{} c @{}} b \\ c \end{array} \middle\vert d \mright)$

\end{document}


Both include an array for the split of b and c vertically centred with respect to a and d. The one uses \middle\vert to set the vertical rule, while the other uses the array vertical rule. You can intermix these.

• Variation: Instead of \begin{array}{@{}c@{}}..\end{array}, package amsmath provides \begin{matrix}...\end{matrix}. – Heiko Oberdiek Jun 22 '18 at 21:24

Two other variants, with delarray or blkarray and \multirowcell from makecell:

\documentclass{article}

\usepackage{amsmath}
\usepackage{blkarray, delarray, multirow, makecell}

\begin{document}

$-\delta^{*}\! \begin{array}({@{}c|c@{}}) 1 + d^{\top}\tau & \multirowcell{2}{W} \\ V^{\top} d + b(x){} \end{array}$

$\begin{blockarray}{c(c|c)} \BAmultirow{1em}{ -\delta^{*} } & 1 + d^{\top}\tau & \BAmultirow{1em}{ W } \\ & V^{\top} d + b(x){} \end{blockarray}$

\end{document}