Multiline equations

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Be sure to also read Using \startalign and friends written by Aditya Mahajan.

Basic Alignment

Two modes of input

  • Latex style
\startformula \startalign
 v &= u + at \\
 h &= ut + \frac12 gt^2 \\
\stopalign \stopformula

Note the \\ in the last line, above. This appears as follows:

  • Context Style
\startformula \startalign
 \NC v \NC = u + at \NR
 \NC h \NC = ut + \frac12 gt^2 \NR
\stopalign \stopformula

(The examples here will focus on the context style, having two styles can be confusing -- Aditya )

Changing the number of columns

The above equations were aligned at =. Suppose you also want the + to align. Well, this is simple in context, simply specify the number of columns with \startalign

\startformula \startalign[n=3]
 \NC v \NC = u \NC+ at \NR
 \NC h \NC= ut \NC+ \frac12 gt^2 \NR
\stopalign \stopformula

Alignment of each column

If you want more control over the formatting, and want the middle column to be center aligned, you can do that by

\startformula \startalign[n=3,align={right,middle,left}]
 \NC v \NC = u \NC+ at \NR
 \NC h \NC= ut \NC+ \frac12 gt^2 \NR
\stopalign \stopformula

This mechanism allows fancier alignments like

\startformula \startalign[n=4,align={left,right,middle,left}]
 \NC \text{We have} \quad \NC v \NC = u \NC+ at \NR
 \NC \text{and}           \NC h \NC= ut \NC+ \frac12 gt^2 \NR
\stopalign \stopformula

Working with equation numbering

aligned equations can be numbered by placing a tag after \NR

\setuplayout[scale=0.8,width=13cm]
\placeformula \startformula \startalign
 \NC v \NC = u + at \NR[eq:v]
 \NC h \NC = ut + \frac12 gt^2 \NR[eq:h]
\stopalign \stopformula 
Equation~(\in[eq:v]) tells the final velocity after time~$t$ and equation~(\in[eq:h]) tells the distance travelled in time~$t$.

The numbering can be changed to a subformula style using \placesubformula instead of \placeformula and numbering the subformulas using \NR[+][a], \NR[+][b], … instead:

\setuplayout[scale=0.8,width=13cm]
\placesubformula \startformula \startalign
 \NC v \NC = u + at \NR[+][eq:v]
 \NC h \NC = ut + \frac12 gt^2 \NR[+][eq:h]
\stopalign \stopformula 
Equation~(\in[eq:v]) tells the final velocity after time~$t$ and equation (\in[eq:h]) tells the distance travelled in time~$t$.

Changing the number of columns

Defining new alignment structures

New alignment can be defined using \definemathalignment. For example, to emulate gather environment of amsmath, we can use

\definemathalignment
    [gather]
    [n=1,align={middle}]

\startformula \startgather
 \NC  ax^2 + bx + c = 0 \NR
 \NC \text{roots} = \frac{ -b \pm \sqrt{b^2 - 4ac}}{2a} \NR
\stopgather \stopformula


Cases

Context provides a \startmathcases \stopmathcases pair to make it easy to get cases.

\startformula
 f(x) = \startmathcases
   \NC x, \NC if $0 \le x \le \frac12$ \NR
   \NC 1-x ,\NC if $\frac12 \le x \le 1$ \NR
\stopmathcases
\stopformula

gives

The cases environment consists of two columns, separated by \NC. The second column is by default in text mode. An alternative way of getting the same result is to define the second column as a mathcolumn with \MC like so:

\startformula
 f(x) = \startmathcases
   \NC x, \MC \text{if } 0 \le x \le \frac12 \NR
   \NC 1-x ,\MC \text{if } \frac12 \le x \le 1 \NR
\stopmathcases
\stopformula

Each line must end with a \NR.

Numbered Cases