Difference between revisions of "Math/Display"

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< [[Math]]|
+
< [[Math]] >
  
 
= Display Math =
 
= Display Math =
  
Display math is enclosed in a <cmd>startformula</cmd> / <cmd>stopformula</cmd> pair. Thus  
+
Display math is enclosed in a {{cmd|startformula}} / {{cmd|stopformula}} pair. Thus  
  
 
<table width="100%" cols="2"><tr valign="top"><td width="50%">
 
<table width="100%" cols="2"><tr valign="top"><td width="50%">
Line 16: Line 16:
  
 
<context>
 
<context>
\setuplayout[scale=0.8,width=8cm]
+
\setuppapersize[A5]
 +
\setuplayout[width=8cm]
 
The famous result (once more) is given by
 
The famous result (once more) is given by
 
\startformula
 
\startformula
Line 26: Line 27:
 
= Numbering Formulae =
 
= Numbering Formulae =
  
ConTeXt provides an easy way to number the display maths equations. Simply, put <cmd>placeformula</cmd> before  <cmd>startformula</cmd> / <cmd>stopformula</cmd> pair and you will get numbered equations. Thus,
+
ConTeXt provides an easy way to number the display maths equations. Simply, put {{cmd|placeformula}} before  {{cmd|startformula}} and you will get numbered equations. Thus,
 
<table width="100%" cols="2"><tr valign="top"><td width="50%">
 
<table width="100%" cols="2"><tr valign="top"><td width="50%">
 
<texcode>
 
<texcode>
Line 39: Line 40:
  
 
<context>
 
<context>
\setuplayout[scale=0.8,width=8cm]
+
\setuppapersize[A5]
 +
\setuplayout[width=8cm]
 
The famous result (once more) is given by
 
The famous result (once more) is given by
 
\placeformula
 
\placeformula
Line 48: Line 50:
 
</td></tr></table>
 
</td></tr></table>
  
The <cmd>placeformula</cmd> command is optional, and produces the equation number; leaving it off produces an unnumbered equation.
+
The {{cmd|placeformula}} command is optional, and produces the equation number; leaving it off produces an unnumbered equation.
  
 
== Changing format of numbers ==
 
== Changing format of numbers ==
You can use <cmd>setupformulas</cmd> to change the format of numbers. For example to get bold numbers inside square brackets use
+
You can use {{cmd|setupformulas}} to change the format of numbers. For example to get bold numbers inside square brackets use
  
 
<table width="100%" cols="2" cellpadding="5"><tr valign="top"><td width="50%">
 
<table width="100%" cols="2" cellpadding="5"><tr valign="top"><td width="50%">
Line 62: Line 64:
  
 
<context>
 
<context>
\setuplayout[scale=0.8,width=8cm]
+
\setuppapersize[A5]
 +
\setuplayout[width=8cm]
 
\setupformulas[left={[},right={]},numberstyle=bold]
 
\setupformulas[left={[},right={]},numberstyle=bold]
 
The famous result (once more) is given by
 
The famous result (once more) is given by
Line 81: Line 84:
 
<table width="100%" cols="2" cellpadding="5"><tr valign="top"><td width="50%">
 
<table width="100%" cols="2" cellpadding="5"><tr valign="top"><td width="50%">
 
<texcode>
 
<texcode>
\setupformulas[conversion=Character]
+
\setupformulas[numberconversion=Character]
 
</texcode>
 
</texcode>
 
</td>
 
</td>
 
<td>which gives
 
<td>which gives
 
<context>
 
<context>
\setuplayout[scale=0.8,width=8cm]
+
\setuppapersize[A5]
\setupformulas[conversion=Character]
+
\setuplayout[width=8cm]
 +
\setupformulas[numberconversion=Character]
 
\placeformula
 
\placeformula
 
\startformula
 
\startformula
Line 101: Line 105:
  
 
<context>
 
<context>
 +
\setuppapersize[A5]
 +
\setuppapersize[A5]
 
\setuplayout[textwidth=8cm]
 
\setuplayout[textwidth=8cm]
 
This is a bit of text for purpose of example.\epar
 
This is a bit of text for purpose of example.\epar
Line 111: Line 117:
 
</context>
 
</context>
  
In the next examples we explicitly align formulas to the left (<cmd>raggedleft</cmd>), center and right (<cmd>raggedright</cmd>):
+
In the next examples we explicitly align formulas to the left ({{cmd|raggedleft}}), center and right ({{cmd|raggedright}}):
  
 
<context source="yes" text="Or in print:">
 
<context source="yes" text="Or in print:">
 +
\setuppapersize[A5]
 
\setuplayout[textwidth=8cm]
 
\setuplayout[textwidth=8cm]
 
\setupformulas[align=left]
 
\setupformulas[align=left]
Line 126: Line 133:
  
 
<context source="yes" text="And the formulas look like:">
 
<context source="yes" text="And the formulas look like:">
 +
\setuppapersize[A5]
 
\setuplayout[textwidth=8cm]
 
\setuplayout[textwidth=8cm]
 
\setupformulas[align=left]
 
\setupformulas[align=left]
Line 135: Line 143:
 
</context>
 
</context>
  
When tracing is turned on (<cmd>tracemathtrue</cmd>) you can visualize the bounding box of the formula,
+
When tracing is turned on ({{cmd|tracemathtrue}}) you can visualize the bounding box of the formula,
  
 
<context>
 
<context>
 +
\setuppapersize[A5]
 
\setuplayout[textwidth=8cm]
 
\setuplayout[textwidth=8cm]
 
\tracemathtrue
 
\tracemathtrue
Line 151: Line 160:
  
 
<context source="yes" text="This time we get a more spacy result.  [Ed. Note: For this example equation, there appears to be no visible change.]">
 
<context source="yes" text="This time we get a more spacy result.  [Ed. Note: For this example equation, there appears to be no visible change.]">
 +
\setuppapersize[A5]
 
\setuplayout[textwidth=8cm]
 
\setuplayout[textwidth=8cm]
 
\setupformulas[align=middle,strut=yes]
 
\setupformulas[align=middle,strut=yes]
Line 160: Line 170:
  
 
<context source="yes">
 
<context source="yes">
 +
\setuppapersize[A5]
 
\setuplayout[textwidth=8cm]
 
\setuplayout[textwidth=8cm]
 
\tracemathtrue
 
\tracemathtrue
Line 170: Line 181:
  
 
<context source="yes">
 
<context source="yes">
 +
\setuppapersize[A5]
 
\setuplayout[textwidth=8cm]
 
\setuplayout[textwidth=8cm]
 
Some example text, again, to show where the right and left margins of the text block are.
 
Some example text, again, to show where the right and left margins of the text block are.
Line 185: Line 197:
  
 
<context source="yes">
 
<context source="yes">
 +
\setuppapersize[A5]
 
\setuplayout[textwidth=8cm]
 
\setuplayout[textwidth=8cm]
 
Some example text, again, to show where the right and left margins of the text block are.
 
Some example text, again, to show where the right and left margins of the text block are.
Line 196: Line 209:
  
 
<context source="yes">
 
<context source="yes">
 +
\setuppapersize[A5]
 
\setuplayout[textwidth=8cm]
 
\setuplayout[textwidth=8cm]
 
\tracemathtrue
 
\tracemathtrue
Line 204: Line 218:
  
 
= Referencing formulae =
 
= Referencing formulae =
Equations can be referred to by simply adding a label to <cmd>placeformula</cmd> and using <cmd>ref</cmd> to create the reference:
+
Equations can be referred to by simply adding a label to {{cmd|placeformula}} and using {{cmd|ref}} to create the reference:
  
 
<table width="100%" cols="2" cellpadding="5"><tr valign="top"><td width="50%">
 
<table width="100%" cols="2" cellpadding="5"><tr valign="top"><td width="50%">
Line 219: Line 233:
  
 
<context>
 
<context>
\setuplayout[scale=0.8,width=8cm]
+
\setuppapersize[A5]
 +
\setuplayout[width=8cm]
 
The famous result (and again) is given by
 
The famous result (and again) is given by
 
\placeformula[formulalabel]
 
\placeformula[formulalabel]
Line 230: Line 245:
 
</td></tr></table>
 
</td></tr></table>
  
Note, that <cmd>ref</cmd> expects to arguments, therefore you need the brackets twice.
+
Note, that {{cmd|ref}} expects two arguments, therefore you need the brackets twice.
  
By default, only the formula number appears as a reference. This can be changed by using <cmd>definereferenceformat</cmd>. For example, to create a command <code>\eqref</code> which shows the formula number in brackets, use
+
By default, only the formula number appears as a reference. This can be changed by using {{cmd|definereferenceformat}}. For example, to create a command <code>\eqref</code> which shows the formula number in brackets, use
 
<texcode>
 
<texcode>
 
\definereferenceformat[eqref][left=(,right=)]
 
\definereferenceformat[eqref][left=(,right=)]
 
</texcode>
 
</texcode>
See [[References]] for more examples of <cmd>definereferenceformat</cmd>.
+
See [[References]] for more examples of {{cmd|definereferenceformat}}.
  
 
=Sub-Formula Numbering=
 
=Sub-Formula Numbering=
Line 242: Line 257:
 
== Automatic Sub-Formula Numbering ==
 
== Automatic Sub-Formula Numbering ==
  
To use subformula numbering, you can use <cmd>startsubformulas</cmd>/<cmd>stopsubformulas</cmd>. For example
+
To use subformula numbering, you can use {{cmd|startsubformulas}}/{{cmd|stopsubformulas}}. For example
  
 
<table width="100%" cols="2"><tr valign="top"><td width="50%">
 
<table width="100%" cols="2"><tr valign="top"><td width="50%">
Line 265: Line 280:
 
</td><td>
 
</td><td>
 
<context>
 
<context>
\setuplayout[scale=0.8,width=8cm]
+
\setuppapersize[A5]
 +
\setuplayout[width=8cm]
 
Examples:
 
Examples:
 
\startsubformulas[eq:1]
 
\startsubformulas[eq:1]
Line 285: Line 301:
 
== The Manual Method ==
 
== The Manual Method ==
  
Sometimes, you need more fine grained control over numbering of subformulas. In that case one can make use of the optional agument of <cmd>placeformula</cmd> command and the related <cmd>placesubformula</cmd> commands which can be used to produce sub-formula numbering.  For example:
+
Sometimes, you need more fine grained control over numbering of subformulas. In that case one can make use of the optional agument of {{cmd|placeformula}} command and the related {{cmd|placesubformula}} commands which can be used to produce sub-formula numbering.  For example:
  
 
<table width="100%" cols="2"><tr valign="top"><td width="50%">
 
<table width="100%" cols="2"><tr valign="top"><td width="50%">
Line 302: Line 318:
 
</td><td>
 
</td><td>
 
<context>
 
<context>
\setuplayout[scale=0.8,width=8cm]
+
\setuppapersize[A5]
 +
\setuplayout[width=8cm]
 
Examples:
 
Examples:
 
\placeformula{a}
 
\placeformula{a}
Line 316: Line 333:
 
</td></tr></table>
 
</td></tr></table>
  
What's going on here is simpler than it might appear at first glance.  Both <cmd>placeformula</cmd> and <cmd>placesubformula</cmd> produce equation numbers with the optional tag added at the end; the sole difference is that the former increments the equation number first, while the latter does not (and thus can be used for the second and subsequent formulas that use the same formula number but presumably have different tags).
+
What's going on here is simpler than it might appear at first glance.  Both {{cmd|placeformula}} and {{cmd|placesubformula}} produce equation numbers with the optional tag added at the end; the sole difference is that the former increments the equation number first, while the latter does not (and thus can be used for the second and subsequent formulas that use the same formula number but presumably have different tags).
  
This is sufficient for cases where the standard ConTeXt equation numbers suffice, and where only one equation number is needed per formula.  However, there are many cases where this is insufficient, and <cmd>placeformula</cmd> defines <cmd>formulanumber</cmd> and <cmd>subformulanumber</cmd> commands, which provide hooks to allow the use of ConTeXt-managed formula numbers with plain TeX equation numbering.  These, when used within a formula, simply return the formula number in properly formatted form, as can be seen in this simple example with plain TeX's <cmd>eqno</cmd>.  Note that the optional tag is inherited from <cmd>placeformula</cmd>.
+
This is sufficient for cases where the standard ConTeXt equation numbers suffice, and where only one equation number is needed per formula.  However, there are many cases where this is insufficient, and {{cmd|placeformula}} defines {{cmd|formulanumber}} and {{cmd|subformulanumber}} commands, which provide hooks to allow the use of ConTeXt-managed formula numbers with plain TeX equation numbering.  These, when used within a formula, simply return the formula number in properly formatted form, as can be seen in this simple example with plain TeX's {{cmd|eqno}}.  Note that the optional tag is inherited from {{cmd|placeformula}}.
  
 
<table width="100%" cols="2"><tr valign="top"><td width="50%">
 
<table width="100%" cols="2"><tr valign="top"><td width="50%">
Line 331: Line 348:
 
</td><td>
 
</td><td>
 
<context>
 
<context>
\setuplayout[scale=0.8,width=8cm]
+
\setuppapersize[A5]
 +
\setuplayout[width=8cm]
 
More examples:
 
More examples:
 
\placeformula{c}
 
\placeformula{c}
Line 341: Line 359:
 
</td></tr></table>
 
</td></tr></table>
  
In order for this to work properly, we need to turn off ConTeXt's automatic formula number placement; thus the <cmd>let</cmd> command to empty <cmd>doplaceformulanumber</cmd>, which must be placed <em>after</em> the start of the formula.  In many practical examples, however, this is not necessary; ConTeXt redefines <cmd>displaylines</cmd> and <cmd>eqalignno</cmd> to do this automatically.
+
In order for this to work properly, we need to turn off ConTeXt's automatic formula number placement; thus the {{cmd|let}} command to empty {{cmd|doplaceformulanumber}}, which must be placed <em>after</em> the start of the formula.  In many practical examples, however, this is not necessary; ConTeXt redefines {{cmd|displaylines}} and {{cmd|eqalignno}} to do this automatically.
  
For more control over sub-formula numbering, <cmd>formulanumber</cmd> and <cmd>subformulanumber</cmd> have an optional argument parallel to that of <cmd>placeformula</cmd>, as demonstrated in this use of plain TeX's <cmd>eqalignno</cmd>, which places multiple equation numbers within one formula.
+
For more control over sub-formula numbering, {{cmd|formulanumber}} and {{cmd|subformulanumber}} have an optional argument parallel to that of {{cmd|placeformula}}, as demonstrated in this use of plain TeX's {{cmd|eqalignno}}, which places multiple equation numbers within one formula.
  
 
<table width="100%" cols="2"><tr valign="top"><td width="50%">
 
<table width="100%" cols="2"><tr valign="top"><td width="50%">
Line 358: Line 376:
 
</td><td>
 
</td><td>
 
<context>
 
<context>
\setuplayout[scale=0.8,width=8cm]
+
\setuppapersize[A5]
 +
\setuplayout[width=8cm]
 
\placeformula
 
\placeformula
 
\startformula
 
\startformula
Line 370: Line 389:
 
</td></tr></table>
 
</td></tr></table>
  
Note that both <cmd>formulanumber</cmd> and <cmd>subformulanumber</cmd> can be used within the same formula, and the formula number is incremented as expected.  Also, if an optional argument is specified in both <cmd>placefigure</cmd> and <cmd>formulanumber</cmd>, the latter takes precedence.
+
Note that both {{cmd|formulanumber}} and {{cmd|subformulanumber}} can be used within the same formula, and the formula number is incremented as expected.  Also, if an optional argument is specified in both {{cmd|placefigure}} and {{cmd|formulanumber}}, the latter takes precedence.
  
 
<table width="100%" cols="2"><tr valign="top"><td width="50%">
 
<table width="100%" cols="2"><tr valign="top"><td width="50%">
Line 391: Line 410:
 
</td><td>
 
</td><td>
 
<context>
 
<context>
\setuplayout[scale=0.8,width=8cm]
+
\setuppapersize[A5]
 +
\setuplayout[width=8cm]
 
More examples for left-located equation no.:
 
More examples for left-located equation no.:
 
\setupformulas[location=left]
 
\setupformulas[location=left]
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=List of Formulas=
 
=List of Formulas=
  
You can have a list of the formulas contained in a document by using <cmd>placenamedformula</cmd> instead of <cmd>placeformula</cmd>. Only the formulas written with <cmd>placenamedformula</cmd> are not put in the list, so that you can control precisely the content of the list.
+
You can have a list of the formulas contained in a document by using {{cmd|placenamedformula}} instead of {{cmd|placeformula}}. Only the formulas written with {{cmd|placenamedformula}} are not put in the list, so that you can control precisely the content of the list.
  
<cmd>placenamedformula</cmd> takes as first parameter the name of the formula put in the list. The other <cmd>placeformula</cmd> features are still available. The list can be formatted like any other list.
+
{{cmd|placenamedformula}} takes as first parameter the name of the formula put in the list. The other {{cmd|placeformula}} features are still available. The list can be formatted like any other list.
  
 
Example:
 
Example:
Line 436: Line 456:
  
 
<context>
 
<context>
\setuplayout[scale=0.8,width=13cm]
+
\setuppapersize[A5]
 +
\setuplayout[width=13cm]
 
\subsubject{List of Formulas}
 
\subsubject{List of Formulas}
 
\placelist[formula][criterium=text,alternative=c]
 
\placelist[formula][criterium=text,alternative=c]
Line 454: Line 475:
 
(see also [[Framed]])
 
(see also [[Framed]])
  
To highlight part of a formula, you can give it a gray background using <cmd>mframed</cmd>:
+
To highlight part of a formula, you can give it a gray background using {{cmd|mframed}}: the following is the code you can use in mkii (see below what one has to do in mkiv):
  
 
<context source="yes">
 
<context source="yes">
 +
\setuppapersize[A5]
 
\setupcolors[state=start]
 
\setupcolors[state=start]
 
\def\graymath{\mframed[frame=off,
 
\def\graymath{\mframed[frame=off,
Line 466: Line 488:
 
   \ln (1+x) =\, \graymath{x - {x^2\over2}} \,+ {x^3\over3}-\cdots.
 
   \ln (1+x) =\, \graymath{x - {x^2\over2}} \,+ {x^3\over3}-\cdots.
 
\stopformula
 
\stopformula
 +
</context>
 +
 +
In mkiv the code is slightly different: one may define {{cmd|graymath}} directly using {{cmd|definemathframed}}
 +
 +
<texcode>
 +
\setuppapersize[A5]
 +
\definemathframed[graymath]
 +
[
 +
frame=off,
 +
location=mathematics,
 +
background=color,
 +
backgroundcolor=lightgray,
 +
backgroundoffset=2pt
 +
]
 +
\starttext
 +
Since for $|x| < 1$ we have
 +
\startformula
 +
\log(1+x) = \graymath{x- \displaystyle{x^2\over2}} + {x^3 \over 3} + \cdots
 +
\stopformula
 +
we may write $\log(1+x) = x + O(x^2)$.
 +
\stoptext
 +
</texcode>
 +
 +
The result is shown below (possibly the framed part of the formula is not aligned correctly with the remainder of the formula because the mkiv engine on Context Garden is not up to date…).
 +
 +
<context mode=mkiv>
 +
\setuppapersize[A5]
 +
\definemathframed[graymath]
 +
[
 +
frame=off,
 +
location=mathematics,
 +
background=color,
 +
backgroundcolor=lightgray,
 +
backgroundoffset=2pt
 +
]
 +
 +
Since for $|x| < 1$ we have
 +
\startformula
 +
\log(1+x) = \graymath{x- \displaystyle{x^2\over2}} + {x^3 \over 3} + \cdots
 +
\stopformula
 +
we may write $\log(1+x) = x + O(x^2)$.
 
</context>
 
</context>

Latest revision as of 16:29, 27 February 2017

< Math >

Display Math

Display math is enclosed in a \startformula / \stopformula pair. Thus

The famous result (once more) is given by
\startformula
c^2 = a^2 + b^2.
\stopformula

This, when typeset, produces the following:

Numbering Formulae

ConTeXt provides an easy way to number the display maths equations. Simply, put \placeformula before \startformula and you will get numbered equations. Thus,

The famous result (once more) is given by
\placeformula
\startformula
c^2 = a^2 + b^2.
\stopformula

This, when typeset, produces the following:

The \placeformula command is optional, and produces the equation number; leaving it off produces an unnumbered equation.

Changing format of numbers

You can use \setupformulas to change the format of numbers. For example to get bold numbers inside square brackets use

 \setupformulas[left={[},right={]},numberstyle=bold]
which gives

To get equations also numbered by section, add the command:

 \setupnumber[formula][way=bysection] 

To the start of your document.

To get alphabets instead of numbers, use

\setupformulas[numberconversion=Character]
which gives

Changing Formula alignment

Normally a formula is centered, but in case you want to align it left or right, you can set up formulas to behave that way. Normally a formula will adapt its left indentation to the environment:

In the next examples we explicitly align formulas to the left (\raggedleft), center and right (\raggedright):

\setuppapersize[A5]
\setuplayout[textwidth=8cm]
\setupformulas[align=left]
\startformula c^2 = a^2 + b^2 \stopformula
\setupformulas[align=middle]
\startformula c^2 = a^2 + b^2 \stopformula
\setupformulas[align=right]
\startformula c^2 = a^2 + b^2 \stopformula

Or in print:

With formula numbers the code is:

\setuppapersize[A5]
\setuplayout[textwidth=8cm]
\setupformulas[align=left]
\placeformula \startformula c^2 = a^2 + b^2 \stopformula
\setupformulas[align=middle]
\placeformula \startformula c^2 = a^2 + b^2 \stopformula
\setupformulas[align=right]
\placeformula \startformula c^2 = a^2 + b^2 \stopformula

And the formulas look like:

When tracing is turned on (\tracemathtrue) you can visualize the bounding box of the formula,

As you can see, the dimensions are the natural ones, but if needed you can force a normalized line:

\setuppapersize[A5]
\setuplayout[textwidth=8cm]
\setupformulas[align=middle,strut=yes]
\tracemathtrue
\placeformula \startformula c^2 = a^2 + b^2 \stopformula

This time we get a more spacy result. [Ed. Note: For this example equation, there appears to be no visible change.]

We will now show a couple of more settings and combinations of settings. In centered formulas, the number takes no space

\setuppapersize[A5]
\setuplayout[textwidth=8cm]
\tracemathtrue
\setupformulas[align=middle]
\startformula c^2 = a^2 + b^2 \stopformula
\placeformula \startformula c^2 = a^2 + b^2 \stopformula

You can influence the placement of the whole box with the parameters leftmargin and rightmargin.

\setuppapersize[A5]
\setuplayout[textwidth=8cm]
Some example text, again, to show where the right and left margins of the text block are.
\tracemathtrue
\setupformulas[align=right,leftmargin=3em]
\startformula c^2 = a^2 + b^2 \stopformula
\placeformula \startformula c^2 = a^2 + b^2 \stopformula

\setupformulas[align=left,rightmargin=1em]
\startformula c^2 = a^2 + b^2 \stopformula
\placeformula \startformula c^2 = a^2 + b^2 \stopformula

You can also inherit the margin from the environment.

\setuppapersize[A5]
\setuplayout[textwidth=8cm]
Some example text, again, to show where the right and left margins of the text block are.
\tracemathtrue
\setupformulas[align=right,margin=standard]
\startformula c^2 = a^2 + b^2 \stopformula
\placeformula \startformula c^2 = a^2 + b^2 \stopformula

The distance between the formula and the number is only applied when the formula is left or right aligned.

\setuppapersize[A5]
\setuplayout[textwidth=8cm]
\tracemathtrue
\setupformulas[align=left,distance=2em]
\startformula c^2 = a^2 + b^2 \stopformula
\placeformula \startformula c^2 = a^2 + b^2 \stopformula

Referencing formulae

Equations can be referred to by simply adding a label to \placeformula and using \ref to create the reference:

The famous result (and again) is given by
\placeformula[formulalabel]
\startformula
c^2 = a^2 + b^2.
\stopformula
And now we can refer to formula \ref[][formulalabel].

This, when typeset, produces the following:

Note, that \ref expects two arguments, therefore you need the brackets twice.

By default, only the formula number appears as a reference. This can be changed by using \definereferenceformat. For example, to create a command \eqref which shows the formula number in brackets, use

\definereferenceformat[eqref][left=(,right=)]

See References for more examples of \definereferenceformat.

Sub-Formula Numbering

Automatic Sub-Formula Numbering

To use subformula numbering, you can use \startsubformulas/\stopsubformulas. For example

Examples:
\startsubformulas[eq:1]
\placeformula[eq:first]
\startformula
  c^2 = a^2 + b^2
\stopformula

\placeformula[eq:second]
\startformula
c^2 = a^2 + b^2
\stopformula
\stopsubformulas
Formula (\in[eq:1]) states 
the Pythagora's Theorem twice,
once in (\in[eq:first]) and 
again in (\in[eq:second]).


The Manual Method

Sometimes, you need more fine grained control over numbering of subformulas. In that case one can make use of the optional agument of \placeformula command and the related \placesubformula commands which can be used to produce sub-formula numbering. For example:

Examples:
\placeformula{a}
\startformula
c^2 = a^2 + b^2
\stopformula

\placesubformula{b}
\startformula
c^2 = a^2 + b^2
\stopformula

What's going on here is simpler than it might appear at first glance. Both \placeformula and \placesubformula produce equation numbers with the optional tag added at the end; the sole difference is that the former increments the equation number first, while the latter does not (and thus can be used for the second and subsequent formulas that use the same formula number but presumably have different tags).

This is sufficient for cases where the standard ConTeXt equation numbers suffice, and where only one equation number is needed per formula. However, there are many cases where this is insufficient, and \placeformula defines \formulanumber and \subformulanumber commands, which provide hooks to allow the use of ConTeXt-managed formula numbers with plain TeX equation numbering. These, when used within a formula, simply return the formula number in properly formatted form, as can be seen in this simple example with plain TeX's \eqno. Note that the optional tag is inherited from \placeformula.

More examples:
\placeformula{c}
\startformula
\let\doplaceformulanumber\empty
c^2 = a^2 + b^2   \eqno{\formulanumber}
\stopformula

In order for this to work properly, we need to turn off ConTeXt's automatic formula number placement; thus the \let command to empty \doplaceformulanumber, which must be placed after the start of the formula. In many practical examples, however, this is not necessary; ConTeXt redefines \displaylines and \eqalignno to do this automatically.

For more control over sub-formula numbering, \formulanumber and \subformulanumber have an optional argument parallel to that of \placeformula, as demonstrated in this use of plain TeX's \eqalignno, which places multiple equation numbers within one formula.

\placeformula
\startformula
\eqalignno{
  c^2 &= a^2 + b^2  &\formulanumber{a} \cr
  c &= \left(a^2 + b^2\right)^{\vfrac{1}{2}} &\subformulanumber{b}\cr
  a^2 + b^2 &= c^2  &\subformulanumber{c} \cr
  d^2 &= e^2        &\formulanumber\cr}
\stopformula

Note that both \formulanumber and \subformulanumber can be used within the same formula, and the formula number is incremented as expected. Also, if an optional argument is specified in both \placefigure and \formulanumber, the latter takes precedence.

More examples for left-located equation number:
\setupformulas[location=left]
\placeformula{d}
\startformula
\let\doplaceformulanumber\empty
c^2 = a^2 + b^2   \leqno{\formulanumber}
\stopformula
and
\placeformula
\startformula
\leqalignno{c^2 &= a^2 + b^2  &\formulanumber{a} \cr
           a^2 + b^2 &= c^2  &\subformulanumber{b} \cr
           d^2 &= e^2        &\formulanumber\cr}
\stopformula

-- 23:46, 15 Aug 2005 (CEST) Prinse Wang

List of Formulas

You can have a list of the formulas contained in a document by using \placenamedformula instead of \placeformula. Only the formulas written with \placenamedformula are not put in the list, so that you can control precisely the content of the list.

\placenamedformula takes as first parameter the name of the formula put in the list. The other \placeformula features are still available. The list can be formatted like any other list.

Example:

\subsubject{List of Formulas}
\placelist[formula][criterium=text,alternative=c]
 
\subsubject{Formulas}
\placenamedformula[one]{First listed Formula}
\startformula a = 1 \stopformula \endgraf

\placeformula
\startformula a = 2 \stopformula \endgraf

\placenamedformula{Second listed Formula}{b}
\startformula a = 3 \stopformula \endgraf

Gives:

Shaded background for part of a displayed equation

(see also Framed)

To highlight part of a formula, you can give it a gray background using \mframed: the following is the code you can use in mkii (see below what one has to do in mkiv):

\setuppapersize[A5]
\setupcolors[state=start]
\def\graymath{\mframed[frame=off,
    background=color,
    backgroundcolor=gray,
    backgroundoffset=3pt]}

\startformula
  \ln (1+x) =\, \graymath{x - {x^2\over2}} \,+ {x^3\over3}-\cdots.
\stopformula

In mkiv the code is slightly different: one may define \graymath directly using \definemathframed

\setuppapersize[A5]
\definemathframed[graymath]
	[
	frame=off,
	location=mathematics,
	background=color,
	backgroundcolor=lightgray,
	backgroundoffset=2pt
	]
\starttext
Since for $|x| < 1$ we have
\startformula
\log(1+x) = \graymath{x- \displaystyle{x^2\over2}} + {x^3 \over 3} + \cdots
\stopformula
we may write $\log(1+x) = x + O(x^2)$.
\stoptext

The result is shown below (possibly the framed part of the formula is not aligned correctly with the remainder of the formula because the mkiv engine on Context Garden is not up to date…).