eqn
—
eqn language reference for mandoc
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.
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 cvalc
The 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 bazc
It 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 for
define
, while
tdefine
is discarded.
gfont
- Set the default font of subsequent output. Its syntax is as follows:
gfont
font
In mandoc, this value is discarded.
gsize
- Set the default size of subsequent output. Its syntax is as follows:
The 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 val
The 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
key
Once 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 in
matrix
.
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 in
matrix
.
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 a
matrix
, corresponding subequations in
all columns line up horizontally, while each
pile
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 in
matrix
.
right
- See
left
;
right
cannot be used without
left
. To set a big right delimiter
without a big left delimiter, the following construction can be used:
left
"" box
right
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 a sub
clause as in
mainbox
sub
subbox
sup
supbox
both 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 a
from
clause as in
mainbox
from
frombox
to
tobox
both 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,
mainbox
sup
supbox
sub
subbox
is the same as
mainbox
sup
{supbox
sub
subbox}
and different from
{mainbox
sup
supbox}
sub
subbox.
By contrast,
over
groups to the left.
In the following list, earlier operations bind more tightly than later
operations:
dyad
,
vec
,
under
,
bar
,
tilde
,
hat
,
dot
,
dotdot
fat
,
roman
,
italic
,
bold
,
size
sub
,
sup
sqrt
over
from
,
to
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 the mark
and lineup
tokens. mandoc discards
these tokens. The back
n, fwd
n, up
n, and
down
n
commands are also ignored.
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.
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.
This
eqn
reference was written by
Kristaps Dzonsons
<
kristaps@bsd.lv>.