Controlling delimiters

If not in compatibility mode, eqn recognizes

to restore the delimiters which have been previously disabled with a call to ‘delim off’. If delimiters haven't been specified, the call has no effect.

Automatic spacing

eqn gives each component of an equation a type, and adjusts the spacing between components using that type. Possible types are described in the table below.

Components of an equation get a type in one of two ways.

type t e

This yields an equation component that contains e but that has type t, where t is one of the types mentioned above. For example, times is defined as

The name of the type doesn't have to be quoted, but quoting protects from macro expansion.

chartype t text

Unquoted groups of characters are split up into individual characters, and the type of each character is looked up; this changes the type that is stored for each character; it says that the characters in text from now on have type t. For example,

would make the characters ‘.,;:’ have type punctuation whenever they subsequently appeared in an equation. The type t can also be letter or digit; in these cases chartype changes the font type of the characters. See subsection “Fonts” below.

New primitives

big e

Enlarges the expression it modifies; intended to have semantics like CSS ‘large’. In troff output, the point size is increased by 5; in MathML output, the expression uses

e1 smallover e2

This is similar to over; smallover reduces the size of e1 and e2; it also puts less vertical space between e1 or e2 and the fraction bar. The over primitive corresponds to the TeX \over primitive in display styles; smallover corresponds to \over in non-display styles.

vcenter e

This vertically centers e about the math axis. The math axis is the vertical position about which characters such as ‘+’ and ‘−’ are centered; also it is the vertical position used for the bar of fractions. For example, sum is defined as

(Note that vcenter is silently ignored when generating MathML.)

e1 accent e2

This sets e2 as an accent over e1. e2 is assumed to be at the correct height for a lowercase letter; e2 is moved down according to whether e1 is taller or shorter than a lowercase letter. For example, hat is defined as

dotdot, dot, tilde, vec, and dyad are also defined using the accent primitive.

e1 uaccent e2

This sets e2 as an accent under e1. e2 is assumed to be at the correct height for a character without a descender; e2 is moved down if e1 has a descender. utilde is pre-defined using uaccent as a tilde accent below the baseline.

split "text"

This has the same effect as simply

but text is not subject to macro expansion because it is quoted; text is split up and the spacing between individual characters is adjusted.

nosplit text

This has the same effect as

but because text is not quoted it is subject to macro expansion; text is not split up and the spacing between individual characters is not adjusted.

e opprime

This is a variant of prime that acts as an operator on e. It produces a different result from prime in a case such as A opprime sub 1: with opprime the 1 is tucked under the prime as a subscript to the A (as is conventional in mathematical typesetting), whereas with prime the 1 is a subscript to the prime character. The precedence of opprime is the same as that of bar and under, which is higher than that of everything except accent and uaccent. In unquoted text a ' that is not the first character is treated like opprime.

special text e

This constructs a new object from e using a troff(1) macro named text. When the macro is called, the string 0s contains the output for e, and the number registers 0w, 0h, 0d, 0skern, and 0skew contain the width, height, depth, subscript kern, and skew of e. (The subscript kern of an object says how much a subscript on that object should be tucked in; the skew of an object says how far to the right of the center of the object an accent over the object should be placed.) The macro must modify 0s so that it outputs the desired result with its origin at the current point, and increase the current horizontal position by the width of the object. The number registers must also be modified so that they correspond to the result.

For example, suppose you wanted a construct that ‘cancels’ an expression by drawing a diagonal line through it.

Then you could cancel an expression e with cancel { e }

Here's a more complicated construct that draws a box round an expression:

space n

A positive value of the integer n (in hundredths of an em) sets the vertical spacing before the equation, a negative value sets the spacing after the equation, replacing the default values. This primitive provides an interface to groff's \x escape (but with opposite sign).

This keyword has no effect if the equation is part of a pic picture.

Extended primitives

col n { ... }

ccol n { ... }

lcol n { ... }

rcol n { ... }

pile n { ... }

cpile n { ... }

lpile n { ... }

rpile n { ... }

The integer value n (in hundredths of an em) increases the vertical spacing between rows, using groff's \x escape (the value has no effect in MathML mode). Negative values are possible but have no effect. If there is more than a single value given in a matrix, the biggest one is used.

Customization

When eqn is generating troff markup, the appearance of equations is controlled by a large number of parameters. They have no effect when generating MathML mode, which pushes typesetting and fine motions downstream to a MathML rendering engine. These parameters can be set using the set command.

set p n

This sets parameter p to value n; n is an integer. For example,

says that eqn should assume an x height of 0.45 ems.

Macros

Macros can take arguments. In a macro body, $n where n is between 1 and 9, is replaced by the nth argument if the macro is called with arguments; if there are fewer than n arguments, it is replaced by nothing. A word containing a left parenthesis where the part of the word before the left parenthesis has been defined using the define command is recognized as a macro call with arguments; characters following the left parenthesis up to a matching right parenthesis are treated as comma-separated arguments; commas inside nested parentheses do not terminate an argument.

sdefine name X anything X

This is like the define command, but name is not recognized if called with arguments.

include "file"

copy "file"

Include the contents of file (include and copy are synonyms). Lines of file beginning with .EQ or .EN are ignored.

ifdef name X anything X

If name has been defined by define (or has been automatically defined because name is the output device) process anything; otherwise ignore anything. X can be any character not appearing in anything.

undef name

Remove definition of name, making it undefined.

Besides the macros mentioned above, the following definitions are available: Alpha, Beta, ..., Omega (this is the same as ALPHA, BETA, ..., OMEGA), ldots (three dots on the base line), and dollar.

Fonts

eqn normally uses at least two fonts to set an equation: an italic font for letters, and a roman font for everything else. The existing gfont command changes the font that is used as the italic font. By default this is I. The font that is used as the roman font can be changed using the new grfont command.

grfont f

Set the roman font to f.

The italic primitive uses the current italic font set by gfont; the roman primitive uses the current roman font set by grfont. There is also a new gbfont command, which changes the font used by the bold primitive. If you only use the roman, italic and bold primitives to changes fonts within an equation, you can change all the fonts used by your equations just by using gfont, grfont and gbfont commands.

You can control which characters are treated as letters (and therefore set in italics) by using the chartype command described above. A type of letter causes a character to be set in italic type. A type of digit causes a character to be set in roman type.