Mathematics/Multiline equations

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 and defining alignment with \definemathalignment

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
  

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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
  

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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
  
  

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Cases

with \startmathcases (two columns)

Context provides a \startmathcases \stopmathcases pair to make it easy to get cases. The cases environment consists of two columns, separated by \NC. Each line must end with a \NR.

• \startformula
   \startcases[align={right,left},distance=3pt]
     \NC 2x + 3y \NC = 10 \NR
     \NC 3x + 2y \NC = 5  \NR
   \stopcases
  \stopformula
  
  and
  
  \startformula
  \delta_{ij} =
   \startmathcases
   \NC 1 \NC \text{if } i = j \NR
   \NC 0 \NC \text{otherwise} \NR
   \stopmathcases
  \stopformula
  

  gives

• 

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
  

  gives

• 

with \definemathmatrix

One of the powerful structures in displaying mathematical formulas is the possibility of defining custom maths alignment. For instance the following definition

• \definemathmatrix
    [alignedcases]            % creates 2 new commands \startalignedcases \stopalignedcases
    [align={right,left,left},
     distance=3pt,
     left={\left\{},
     right={\right.},
     style=\displaystyle]
  
  The following formula is displayed in two lines with an appropriate alignment of the equations:
  
  \startformula
  \startalignedcases
   \NC -\Delta u + g(u) \NC{} = f \NC \quad\mbox{in } \Omega\NR
   \NC {\partial u \over \partial {\bf n} } \NC{} = h(u) \NC \quad\mbox{on } \partial\Omega   \NR
  \stopalignedcases
  \stopformula
  

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Numbering cases with \startplaceformula plus \startsubformulas

As you may expect:

• \startsubformulas
  \startplaceformula
  \startformula
   \startcases[align={right,left},distance=3pt]
     \NC 2x + 3y \NC = 10 \NR[eq:a]
     \NC 3x + 2y \NC = 5  \NR[eq:b]
   \stopcases
  \stopformula
  \stopplaceformula
  \stopsubformulas
  

  gives

•