NAME
eqn
—
eqn language reference for
mandoc
DESCRIPTION
The eqn
language is an equation-formatting
language. It is used within
mdoc(7) and man(7) UNIX manual pages. It
describes the
structure
of an equation, not its mathematical meaning. This manual describes the
eqn
language accepted by the
mandoc(1) utility, which corresponds to the Second Edition
eqn
specification (see
SEE ALSO for references).
Equations within mdoc(7) or man(7) documents are enclosed by the standalone ‘.EQ’ and ‘.EN’ tags. Equations are multi-line blocks consisting of formulas and control statements.
EQUATION STRUCTURE
Each equation is bracketed by ‘.EQ’ and ‘.EN’ strings. Note: these are not the same as roff(7) macros, and may only be invoked as ‘.EQ’.
The equation grammar is as follows, where quoted strings are case-sensitive literals in the input:
eqn : box | eqn box box : text | "{" eqn "}" | "define" text text | "ndefine" text text | "tdefine" text text | "gfont" text | "gsize" text | "set" text text | "undef" text | "sqrt" box | box pos box | box mark | "matrix" "{" [col "{" list "}"]* "}" | pile "{" list "}" | font box | "size" text box | "left" text eqn ["right" text] col : "lcol" | "rcol" | "ccol" | "col" text : [^space\"]+ | \".*\" pile : "lpile" | "cpile" | "rpile" | "pile" pos : "over" | "sup" | "sub" | "to" | "from" mark : "dot" | "dotdot" | "hat" | "tilde" | "vec" | "dyad" | "bar" | "under" font : "roman" | "italic" | "bold" | "fat" list : eqn | list "above" eqn space : [\^~ \t]
White-space consists of the space, tab, circumflex, and tilde characters. It is required to delimit tokens consisting of alphabetic characters and it is ignored at other places. Braces and quotes also delimit tokens. If within a quoted string, these space characters are retained. Quoted strings are also not scanned for keywords, glyph names, and expansion of definitions. To print a literal quote character, it can be prepended with a backslash or expressed with the \(dq escape sequence.
Subequations can be enclosed in braces to pass them as arguments to operation keywords, overriding standard operation precedence. Braces can be nested. To set a brace verbatim, it needs to be enclosed in quotes.
The following text terms are translated into a rendered glyph, if available: alpha, beta, chi, delta, epsilon, eta, gamma, iota, kappa, lambda, mu, nu, omega, omicron, phi, pi, psi, rho, sigma, tau, theta, upsilon, xi, zeta, DELTA, GAMMA, LAMBDA, OMEGA, PHI, PI, PSI, SIGMA, THETA, UPSILON, XI, inter (intersection), union (union), prod (product), int (integral), sum (summation), grad (gradient), del (vector differential), times (multiply), cdot (center-dot), nothing (zero-width space), approx (approximately equals), prime (prime), half (one-half), partial (partial differential), inf (infinity), >> (much greater), << (much less), <- (left arrow), -> (right arrow), +- (plus-minus), != (not equal), == (equivalence), <= (less-than-equal), and >= (more-than-equal). The character escape sequences documented in mandoc_char(7) can be used, too.
The following control statements are available:
define
- Replace all occurrences of a key with a value. Its syntax is as follows:
define
key cvalcThe first character of the value string, c, is used as the delimiter for the value val. This allows for arbitrary enclosure of terms (not just quotes), such as
define
foo 'bar baz'define
foo cbar bazcIt is an error to have an empty key or val. Note that a quoted key causes errors in some
eqn
implementations and should not be considered portable. It is not expanded for replacements. Definitions may refer to other definitions; these are evaluated recursively when text replacement occurs and not when the definition is created.Definitions can create arbitrary strings, for example, the following is a legal construction.
define foo 'define' foo bar 'baz'
Self-referencing definitions will raise an error. The
ndefine
statement is a synonym fordefine
, whiletdefine
is discarded. gfont
- Set the default font of subsequent output. Its syntax is as follows:
gfont
fontIn mandoc, this value is discarded.
gsize
- Set the default size of subsequent output. Its syntax is as follows:
gsize
[+|-]sizeThe size value should be an integer. If prepended by a sign, the font size is changed relative to the current size.
set
- Set an equation mode. In mandoc, both arguments are thrown away. Its
syntax is as follows:
set
key valThe key and val are not expanded for replacements. This statement is a GNU extension.
undef
- Unset a previously-defined key. Its syntax is as follows:
define
keyOnce invoked, the definition for key is discarded. The key is not expanded for replacements. This statement is a GNU extension.
Operation keywords have the following semantics:
above
- See
pile
. bar
- Draw a line over the preceding box.
bold
- Set the following box using bold font.
ccol
- Like
cpile
, but for use inmatrix
. cpile
- Like
pile
, but with slightly increased vertical spacing. dot
- Set a single dot over the preceding box.
dotdot
- Set two dots (dieresis) over the preceding box.
dyad
- Set a dyad symbol (left-right arrow) over the preceding box.
fat
- A synonym for
bold
. font
- Set the second argument using the font specified by the first argument;
currently not recognized by the
mandoc(1)
eqn
parser. from
- Set the following box below the preceding box, using a slightly smaller font. Used for sums, integrals, limits, and the like.
hat
- Set a hat (circumflex) over the preceding box.
italic
- Set the following box using italic font.
lcol
- Like
lpile
, but for use inmatrix
. left
- Set the first argument as a big left delimiter before the second argument.
As an optional third argument,
right
can follow. In that case, the fourth argument is set as a big right delimiter after the second argument. lpile
- Like
cpile
, but subequations are left-justified. matrix
- Followed by a list of columns enclosed in braces. All columns need to have
the same number of subequations. The columns are set as a matrix. The
difference compared to multiple subsequent
pile
operators is that in amatrix
, corresponding subequations in all columns line up horizontally, while eachpile
does vertical spacing independently. over
- Set a fraction. The preceding box is the numerator, the following box is the denominator.
pile
- Followed by a list of subequations enclosed in braces, the subequations
being separated by
above
keywords. Sets the subequations one above the other, each of them centered. Typically used to represent vectors in coordinate representation. rcol
- Like
rpile
, but for use inmatrix
. right
- See
left
;right
cannot be used withoutleft
. To set a big right delimiter without a big left delimiter, the following construction can be used:left
"" boxright
delimiter roman
- Set the following box using the default font.
rpile
- Like
cpile
, but subequations are right-justified. size
- Set the second argument with the font size specified by the first argument; currently ignored by mandoc(1). By prepending a plus or minus sign to the first argument, the font size can be selected relative to the current size.
sqrt
- Set the square root of the following box.
sub
- Set the following box as a subscript to the preceding box.
sup
- Set the following box as a superscript to the preceding box. As a special
case, if a
sup
clause immediately follows asub
clause as inmainboxsub
subboxsup
supboxboth are set with respect to the same mainbox, that is, supbox is set above subbox.
tilde
- Set a tilde over the preceding box.
to
- Set the following box above the preceding box, using a slightly smaller
font. Used for sums and integrals and the like. As a special case, if a
to
clause immediately follows afrom
clause as inmainboxfrom
fromboxto
toboxboth are set below and above the same mainbox.
under
- Underline the preceding box.
vec
- Set a vector symbol (right arrow) over the preceding box.
The binary operations from
,
to
, sub
, and
sup
group to the right, that is,
sup
supbox
sub
subboxis the same as
sup
{supbox
sub
subbox}and different from
sup
supbox}
sub
subboxBy contrast, over
groups to the left.
In the following list, earlier operations bind more tightly than later operations:
COMPATIBILITY
This section documents the compatibility of mandoc
eqn
and the troff eqn
implementation (including GNU troff).
- The text string ‘\"’ is interpreted as a literal quote in troff. In mandoc, this is interpreted as a comment.
- In troff, The circumflex and tilde white-space symbols map to fixed-width spaces. In mandoc, these characters are synonyms for the space character.
- The troff implementation of
eqn
allows for equation alignment with themark
andlineup
tokens. mandoc discards these tokens. Theback
n,fwd
n,up
n, anddown
n commands are also ignored.
SEE ALSO
mandoc(1), man(7), mandoc_char(7), mdoc(7), roff(7)
Brian W. Kernighan and Lorinda L. Cherry, System for Typesetting Mathematics, Communications of the ACM, 18, 151–157, March, 1975.
Brian W. Kernighan and Lorinda L. Cherry, Typesetting Mathematics, User's Guide, 1976.
Brian W. Kernighan and Lorinda L. Cherry, Typesetting Mathematics, User's Guide (Second Edition), 1978.
HISTORY
The eqn utility, a preprocessor for troff, was originally written by Brian W. Kernighan and Lorinda L. Cherry in 1975. The GNU reimplementation of eqn, part of the GNU troff package, was released in 1989 by James Clark. The eqn component of mandoc(1) was added in 2011.
AUTHORS
This eqn
reference was written by
Kristaps Dzonsons
<kristaps@bsd.lv>.