Multiline equations
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Be sure to also read Using \startalign and friends written by Aditya Mahajan.
Contents
Basic Alignment with \startalign
\startformula\startalign \NC v \NC = u + at \NR \NC h \NC = ut + \frac12 gt^2 \NR \stopalign\stopformula
\NC stands for new column, \NR stands for new row.
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
Equation numbering with \startplaceformula
Aligned equations can be numbered by using \startplaceformula (as usual), and by placing a tag after \NR
\setuplayout[scale=0.8,width=13cm] \startplaceformula \startformula \startalign \NC v \NC = u + at \NR[eq:v] \NC h \NC = ut + \frac12 gt^2 \NR[eq:h] \stopalign \stopformula \stopplaceformula Equation~(\in[eq:v]) tells the final velocity after time~$t$ and equation~(\in[eq:h]) tells the distance travelled in time~$t$.
Sub-numbering with \startsubformulas
The numbering can be changed to a subformula style by encapsulating \startplaceformula with \startsubformulas :
\setuplayout[scale=0.8,width=13cm] \startsubformulas[eq:total] \startplaceformula \startformula \startalign \NC v \NC = u + at \NR[eq:v] \NC h \NC = ut + \frac12 gt^2 \NR[eq:h] \stopalign \stopformula \stopplaceformula \stopsubformulas In~(\in[eq:total]), equation~(\in[eq:v]) tells the final velocity after time~$t$ and equation (\in[eq:h]) tells the distance travelled in time~$t$.
Specifying alignment and defining new alignment structures
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={1:right,2:middle,3: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={1:right,2:right,3:middle,4:left}] \NC \text{We have} \quad \NC v \NC = u \NC+ at \NR \NC \text{and} \quad \NC h \NC= ut \NC+ \frac12 gt^2 \NR \stopalign \stopformula
These kind of new alignment can be defined using \definemathalignment.
\definemathalignment [demom] [n=4,align={1:right,2:right,3:middle,4:left}] \startformula \startdemom \NC \text{We have} \quad \NC v \NC = u \NC+ at \NR \NC \text{and} \quad \NC h \NC= ut \NC+ \frac12 gt^2 \NR \stopdemom \stopformula
A second example, to emulate gather
environment of amsmath, we can use
\definemathalignment [gather] [n=1,align={1: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 \delta_{ij} = \startmathcases \NC 1 \NC \text{if } i = j \NR \NC 0 \NC \text{otherwise} \NR \stopmathcases \stopformula
gives
The cases environment consists of two columns, separated by \NC. The second column is by default in math mode. To typeset the second column in text mode, use \TC
\startformula \delta_{ij} = \startmathcases \NC 1 \TC if \m{i = j} \NR \NC 0 \TC otherwise \NR \stopmathcases \stopformula
Each line must end with a \NR.