%% This is part of the OpTeX project, see http://petr.olsak.net/optex
% Math alignment examples inspired by https://www.ntg.nl/maps/34/06.pdf
\fontfam[newcm]
\margins/1 a4 (2,2,2,2)cm
\hyperlinks\Blue\Blue
\refdecl{
\def\Xpos#1#2#3{\sxdef{pos:#1}{{#2}{#3}\_currpage}}
}
\def\setpos[#1]{\openref\pdfsavepos
\_ewref\Xpos{{#1}\unexpanded{{\the\pdflastxpos}{\the\pdflastypos}}}}
\def\posx [#1]{\_ea \posi \romannumeral-`\.\trycs{pos:#1}{{0}{0}{0}{0}}sp}
\def\posy [#1]{\_ea \posii \romannumeral-`\.\trycs{pos:#1}{{0}{0}{0}{0}}sp}
\def\pospg[#1]{\_ea \posiii \romannumeral-`\.\trycs{pos:#1}{{0}{0}{0}{0}}}
\def\posi #1#2#3#4{#1}
\def\posii #1#2#3#4{#2}
\def\posiii #1#2#3#4{#3}
\newcount\tomarginno
\def\toright#1{\_incr\tomarginno {\setpos[tr:\the\tomarginno]%
\rlap{\kern-\posx[tr:\the\tomarginno]\kern\hoffset\kern\hsize\llap{#1}}}}
\def\toleft#1{\_incr\tomarginno {\setpos[tr:\the\tomarginno]%
\rlap{\kern-\posx[tr:\the\tomarginno]\kern\hoffset\rlap{#1}}}}
\def\eqm{\toright\eqmark}
\def\\{\begingroup
\_setverb \obeylines \scanlatex
}
\def\scanlatex#1//{\tt #1\endgroup \scanoptex}
\long\def\scanoptex#1$${\begingroup
\_setverb \obeylines \scanoptexA
}
\ea\def\ea\scanoptexA\ea#\ea1\detokenize{$$}{\bigskip \tt
\detokenize{$$}#1\detokenize{$$}\endgroup
$$\catcode`\^^M=9 \scantextokens{#1}$$
\bigskip
}
\tit Math alignment examples
The document \url{https://www.ntg.nl/maps/34/06.pdf} shows examples how to
do special math alignments in display mode in \ConTeXt/ (and in \LaTeX/ for
comparison). We present the same examples here. They are created in
\OpTeX/ and the \LaTeX/ source is shown for comparison.
Note that several examples here use the macro \code{\\eqm} for placing
an equation mark. The macro is defined~by
\begtt
\def\eqm{\toright\eqmark}
\endtt
%
and the \code{\\toright} macro is defined in
\ulink[http://petr.olsak.net/optex/optex-tricks.html#torighteq]{\OpTeX/ trick 0028}
which is based on
\ulink[http://petr.olsak.net/optex/optex-tricks.html#setpos]{\OpTeX/ trick 0020}.
I.e. the following macros are used here:
\begtt
\refdecl{
\def\Xpos#1#2#3{\sxdef{pos:#1}{{#2}{#3}\_currpage}}
}
\def\setpos[#1]{\openref\pdfsavepos
\_ewref\Xpos{{#1}\unexpanded{{\the\pdflastxpos}{\the\pdflastypos}}}}
\def\posx [#1]{\_ea \posi \romannumeral-`\.\trycs{pos:#1}{{0}{0}{0}{0}}sp}
\def\posy [#1]{\_ea \posii \romannumeral-`\.\trycs{pos:#1}{{0}{0}{0}{0}}sp}
\def\pospg[#1]{\_ea \posiii \romannumeral-`\.\trycs{pos:#1}{{0}{0}{0}{0}}}
\def\posi #1#2#3#4{#1}
\def\posii #1#2#3#4{#2}
\def\posiii #1#2#3#4{#3}
\newcount\tomarginno
\def\toright#1{\_incr\tomarginno {\setpos[tr:\the\tomarginno]%
\rlap{\kern-\posx[tr:\the\tomarginno]\kern\hoffset\kern\hsize\llap{#1}}}}
\def\toleft#1{\_incr\tomarginno {\setpos[tr:\the\tomarginno]%
\rlap{\kern-\posx[tr:\the\tomarginno]\kern\hoffset\rlap{#1}}}}
\endtt
%
and we have to run \TeX/ twice.
\notoc\nonum\sec Contents
\centerline{\vbox{\hsize=.5\hsize
\maketoc
}}
\vfil\break
\let\_firstnoindent=\relax
\mathsboff \catcode`\_=12 \everytable{\catcode`\_=11}
\sec Gather
\\
\begin{gather}
v = u + at, \\
d = ut + \frac12 at^2.
\end{gather}
//
$$
\displaylines{
v = u + at, \eqm \cr
d = ut + {1\over2} at^2. \eqm
}
$$
\sec Left gather
\\
\begin{align}
& v = u + at, \\
& d = ut + \frac12 at^2.
\end{align}
//
$$
\eqalignno{
& v = u + at, & \eqmark \cr
& d = ut + {1\over2} at^2. & \eqmark
}
$$
\sec Right gather
\\
\begin{align}
v = u + at , & \\
d = ut + \frac12 atˆ2. &
\end{align}
//
$$
\eqalignno{
v = u + at, && \eqmark \cr
d = ut + {1\over2} at^2. && \eqmark
}
$$
\sec Align
\\
\begin{align}
v &= u + at, \\
d &= ut + \frac12 at^2.
\end{align}
//
$$
\eqalignno{
v &= u + at, & \eqmark \cr
d &= ut + {1\over2} at^2. & \eqmark
}
$$
\sec Split
\\
\begin{equation} \begin{split}
(x+1)^8 ={} & x^8 + 8 x^7 + 28 x^6 + 56 x^5 + 70 x^4 \\
& + 56 x^3 + 28 x^2 + 8 x + 1.
\end{split} \end{equation}
//
$$
\eqalign{
(x+1)^8 = {}& x^8 + 8 x^7 + 28 x^6 + 56 x^5 + 70 x^4 \cr
& + 56 x^3 + 28 x^2 + 8 x + 1.
} \eqmark
$$
\sec Alignat
\\
\begin{alignat}{2}
\nabla\cdot \mathbf E &= \frac{\rho}{\varepsilon_0}, \qquad
& \nabla\times \mathbf E &= -\frac{\partial \mathbf B}{\partial t},\\
\nabla\cdot \mathbf B &= 0,
& \nabla\times \mathbf B &= \mu_0{\mathbf j}+\varepsilon_0\mu_0
\frac{\partial \mathbf E}{\partial t}.
\end{alignat}
//
$$
\eqalign{
\nabla\cdot {\bf E} &= {\rho\over\varepsilon_0}, \qquad
&& \nabla\times {\bf E} &= -{\partial {\bf B}\over\partial t}, \eqm\cr
\nabla\cdot {\bf B} &= 0,
&& \nabla\times {\bf B} &= \mu_0{\bf j}+\varepsilon_0\mu_0
{\partial {\bf E}\over \partial t}. \eqm
}
$$
\sec Flalign
\\
\begin{flalign*}
\nabla\cdot \mathbf E &= \frac{\rho}{\varepsilon_0},
& \nabla\times \mathbf E &= -\frac{\partial \mathbf B}{\partial t}.\\
\nabla\cdot \mathbf B &= 0,
& \nabla\times \mathbf B &= \mu_0{\mathbf j}+\varepsilon_0\mu_0
\frac{\partial \mathbf E}{\partial t}.
\end{flalign*}
//
$$
\eqspace=10em
\eqalign{
\nabla\cdot {\bf E} &= {\rho\over\varepsilon_0}, \qquad
&& \nabla\times {\bf E} &= -{\partial {\bf B}\over\partial t}, \cr
\nabla\cdot {\bf B} &= 0,
&& \nabla\times {\bf B} &= \mu_0{\bf j}+\varepsilon_0\mu_0
{\partial {\bf E}\over \partial t}.
}
$$
\sec Intertext
\\
\begin{align*}
\cos 2\theta &= \cos^2 \theta + \sin^2 \theta \\
\intertext{replace $\sin^2 \theta$ by $1 - \cos^2 \theta$}
&= 2\cos^2 \theta - 1
\end{align*}
//
$$
\eqalignno{
\cos 2\theta &= \cos^2 \theta + \sin^2 \theta \cr
\noalign{\hbox{replace $\sin^2 \theta$ by $1 - \cos^2 \theta$}}
&= 2\cos^2 \theta - 1
}
$$
\sec Linear equations
\\
\begin{alignat}{5}
x_1 & {} + {}& x_2 &{} + {}& 6x_3 &{} = {}& 170, \\
3x_1 & {} - {}& 110x_2 &{} - {}& x_3 &{} = {}& 4, \\
14x_1 & {} + {}& 13x_2 &{} + {}& 10x_3 &{} = {}& 25.
\end{alignat}
//
$$
\thistable{\tablinespace=0pt \tabiteml={${}}\tabitemr={{}$}
\tabstrut={\lower1.5ex\vbox to3.5ex{}}}
\table{3{rc}r}{
x_1 &+& x_2 &+& 6x_3 &=& 170, \eqm \cr
3x_1 &-& 110x_2 &-& x_3 &=& 4, \eqm \cr
14x_1 &+& 13x_2 &+& 10x_3 &=& 25. \eqm
}
$$
\sec Matrix and Arrays
\\
\begin{equation*}
\setlength{\arraycolsep}{1em}
\begin{array}{ccc}
A & B & C \\
AA & BB & CC \\
AAA & BBB & CCC
\end{array}
\end{equation*}
//
$$
\matrix{
A & B & C \cr
AA & BB & CC \cr
AAA & BBB & CCC
}
$$
\\
\begin{equation*}
\setlength{\arraycolsep}{1em}
\begin{array}{lcr}
A & B & C \\
AA & BB & CC \\
AAA & BBB & CCC
\end{array}
\end{equation*}
//
$$
\thistable{\tabstrut{}\tabiteml={\kern.5em${}}\tabitemr={{}$\kern.5em}}
\table{lcr}{
A & B & C \cr
AA & BB & CC \cr
AAA & BBB & CCC
}
$$
\sec Pmatrix
\\
\begin{equation*}
A = \begin{pmatrix} 1 \\ 2 \\ 3 \end{pmatrix}
\end{equation*}
//
$$
\pmatrix {1\cr 2\cr 3}
$$
\sec Delarray package
\\
\begin{equation*}
\begin{array}[b]({c}) 1 \\ 2 \\ 3 \end{array}
\begin{array}[c]({c}) 1 \\ 2 \\ 3 \end{array}
\begin{array}[t]({c}) 1 \\ 2 \\ 3 \end{array}
\end{equation*}
//
$$
\def\mybox#1{\hbox{$\displaystyle{#1}$}}
\raise3ex\mybox{\pmatrix {1\cr 2\cr 3}}
\pmatrix {1\cr 2\cr 3}
\lower3ex\mybox{\pmatrix {1\cr 2\cr 3}}
$$
\sec Cases
\\
\begin{equation*}
|x| =
\begin{cases}
x, & \text{if $x \ge 0$;} \\
-x, & \text{otherwise.}
\end{cases}
\end{equation*}
//
$$
|x| = \cases { x & if $x \ge 0$; \cr
-x & otherwise }
$$
\\
\begin{equation*}
f(x) =
\begin{dcases}
\int_0ˆx g(y)\,dy, & \text{if $x \ge 0$;} \\
\int_{-x}ˆ0 g(y)\,dy, & \text{otherwise.}
\end{dcases}
\end{equation*}
//
$$
\let\ds=\displaystyle
f(x) = \cases { \ds \int_0^x g(y)\,dy, & if $x \ge 0$; \cr \noalign{\medskip}
\ds \int_{-x}^0 g(y)\,dy, & otherwise. }
$$
\end