# CentOS 7.0 - man page for geqn (centos section 1)

EQN(1)							      General Commands Manual							    EQN(1)

NAME
eqn - format equations for troff or MathML

SYNOPSIS
eqn [-rvCNR] [-d xy] [-T name] [-M dir] [-f F] [-s n] [-p n] [-m n] [files...]

DESCRIPTION
This  manual  page  describes  the GNU version of eqn, which is part of the groff document formatting system.  eqn compiles descriptions of
equations embedded within troff input files into commands that are understood by troff.	Normally, it should be invoked using the -e option
of  groff.   The syntax is quite compatible with Unix eqn.  The output of GNU eqn cannot be processed with Unix troff; it must be processed
with GNU troff.	If no files are given on the command line, the standard input is read.	A filename of - causes the standard  input  to	be

eqn  searches for the file eqnrc in the directories given with the -M option first, then in /etc/groff/site-tmac, /etc/groff/site-tmac, and
finally in the standard macro directory /usr/share/groff/1.22.2/tmac.  If it exists, eqn processes it before the other input files.  The -R
option prevents this.

GNU  eqn does not provide the functionality of neqn: it does not support low-resolution, typewriter-like devices (although it may work ade-
quately for very simple input).

OPTIONS
It is possible to have whitespace between a command line option and its parameter.

-dxy   Specify delimiters x and y for the left and right end, respectively, of in-line equations.  Any delim statements in the source  file
overrides this.

-C     Recognize  .EQ and .EN even when followed by a character other than space or newline.  Also, the statement delim on' is not handled
specially.

-N     Don't allow newlines within delimiters.  This option allows eqn to recover better from missing closing delimiters.

-v     Print the version number.

-r     Only one size reduction.

-mn    The minimum point-size is n.  eqn does not reduce the size of subscripts or superscripts to a smaller size than n.

-Tname The output is for device name.  Normally, the only effect of this is to define a macro name with a value of 1; eqnrc  uses  this	to
provide  definitions  appropriate  for the output device.  However, if the specified device is "MathML", the output is MathML markup
rather than troff commands, and eqnrc is not loaded at all.  The default output device is ps.

-Mdir  Search dir for eqnrc before the default directories.

-fF    This is equivalent to a gfont F command.

-sn    This is equivalent to a gsize n command.	This option is deprecated.  eqn normally sets equations at whatever the current point size
is when the equation is encountered.

-pn    This  says  that subscripts and superscripts should be n points smaller than the surrounding text.  This option is deprecated.  Nor-
mally eqn sets subscripts and superscripts at 70% of the size of the surrounding text.

USAGE
Only the differences between GNU eqn and Unix eqn are described here.

GNU eqn emits Presentation MathML output when invoked with the -T MathML option.

GNU eqn sets the input token "..."  as three periods or low dots, rather than the three centered dots of classic eqn.  To  get  three  cen-
tered dots, write cdots or cdot cdot cdot.

Most  of the new features of the GNU eqn input language are based on TeX.  There are some references to the differences between TeX and GNU
eqn below; these may safely be ignored if you do not know TeX.

Controlling delimiters
If not in compatibility mode, eqn recognizes

delim on

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:

ordinary	   an ordinary character such as 1' or x';
_
operator	   a large operator such as >';

binary	   a binary operator such as +';

relation	   a relation such as =';

opening	   a opening bracket such as (';

closing	   a closing bracket such as )';

punctuation  a punctuation character such as ,';

inner	   a subformula contained within brackets;

suppress	   spacing that suppresses automatic spacing adjustment.

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

type "binary" \(mu

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,

chartype "punctuation" .,;:

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 the Fonts subsection.

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

<mstyle mathsize='big'>

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

{ type "operator" vcenter size +5 \(*S }

(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

accent { "^" }

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

text

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

nosplit text
This has the same effect as

"text"

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

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 typeset-
ting), 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.

.EQ
define cancel 'special Ca'
.EN
.de Ca
.	ds 0s \
\Z'\\*(0s'\
\v'\\n(0du'\
\D'l \\n(0wu -\\n(0hu-\\n(0du'\
\v'\\n(0hu'
..

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

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

.EQ
define box 'special Bx'
.EN
.de Bx
.	ds 0s \
\Z'\h'1n'\\*(0s'\
\Z'\
\v'\\n(0du+1n'\
\D'l \\n(0wu+2n 0'\
\D'l 0 -\\n(0hu-\\n(0du-2n'\
\D'l -\\n(0wu-2n 0'\
\D'l 0 \\n(0hu+\\n(0du+2n'\
'\
\h'\\n(0wu+2n'
.	nr 0w +2n
.	nr 0d +1n
.	nr 0h +1n
..

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 oppo-
site 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,

set x_height 45

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

Possible	parameters  are  as  follows.  Values are in units of hundredths of an em unless otherwise stated.  These descriptions are
intended to be expository rather than definitive.

minimum_size
eqn doesn't set anything at a smaller point-size than this.  The value is in points.

fat_offset
The fat primitive emboldens an equation by overprinting two copies of the equation horizontally offset by this amount.   This
parameter is not used in MathML mode; instead, fat text uses

<mstyle mathvariant='double-struck'>

over_hang
A	fraction  bar  is  longer  by  twice this amount than the maximum of the widths of the numerator and denominator; in other
words, it overhangs the numerator and denominator by at least this amount.

accent_width
When bar or under is applied to a single character, the line is this long.  Normally, bar or  under  produces  a  line  whose
length  is  the width of the object to which it applies; in the case of a single character, this tends to produce a line that
looks too long.

delimiter_factor
Extensible delimiters produced with the left and right primitives have a combined height and depth  of  at  least	this  many
thousandths of twice the maximum amount by which the sub-equation that the delimiters enclose extends away from the axis.

delimiter_shortfall
Extensible  delimiters produced with the left and right primitives have a combined height and depth not less than the differ-
ence of twice the maximum amount by which the sub-equation that the delimiters enclose extends away from the  axis  and  this
amount.

null_delimiter_space
This much horizontal space is inserted on each side of a fraction.

script_space
The width of subscripts and superscripts is increased by this amount.

thin_space
This amount of space is automatically inserted after punctuation characters.

medium_space
This amount of space is automatically inserted on either side of binary operators.

thick_space
This amount of space is automatically inserted on either side of relations.

x_height
The height of lowercase letters without ascenders such as x'.

axis_height
The  height  above  the baseline of the center of characters such as +' and -'.	It is important that this value is correct
for the font you are using.

default_rule_thickness
This should set to the thickness of the \(ru character, or the thickness of horizontal lines  produced  with  the	\D  escape
sequence.

num1   The over command shifts up the numerator by at least this amount.

num2   The smallover command shifts up the numerator by at least this amount.

denom1 The over command shifts down the denominator by at least this amount.

denom2 The smallover command shifts down the denominator by at least this amount.

sup1   Normally superscripts are shifted up by at least this amount.

sup2   Superscripts within superscripts or upper limits or numerators of smallover fractions are shifted up by at least this amount.
This is usually less than sup1.

sup3   Superscripts within denominators or square roots or subscripts or lower limits are shifted up by at least this amount.   This
is usually less than sup2.

sub1   Subscripts are normally shifted down by at least this amount.

sub2   When there is both a subscript and a superscript, the subscript is shifted down by at least this amount.

sup_drop
The baseline of a superscript is no more than this much amount below the top of the object on which the superscript is set.

sub_drop
The baseline of a subscript is at least this much below the bottom of the object on which the subscript is set.

big_op_spacing1
The baseline of an upper limit is at least this much above the top of the object on which the limit is set.

big_op_spacing2
The baseline of a lower limit is at least this much below the bottom of the object on which the limit is set.

big_op_spacing3
The bottom of an upper limit is at least this much above the top of the object on which the limit is set.

big_op_spacing4
The top of a lower limit is at least this much below the bottom of the object on which the limit is set.

big_op_spacing5
This much vertical space is added above and below limits.

baseline_sep
The  baselines of the rows in a pile or matrix are normally this far apart.  In most cases this should be equal to the sum of
num1 and denom1.

shift_down
The midpoint between the top baseline and the bottom baseline in a matrix or pile is shifted down by this much from the axis.
In most cases this should be equal to axis_height.

column_sep
This much space is added between columns in a matrix.

matrix_side_sep
This much space is added at each side of a matrix.

draw_lines
If this is non-zero, lines are drawn using the \D escape sequence, rather than with the \l escape sequence and the \(ru char-
acter.

body_height
The amount by which the height of the equation exceeds this is added as extra space before the line containing  the  equation
(using \x).  The default value is 85.

body_depth
The  amount  by  which  the depth of the equation exceeds this is added as extra space after the line containing the equation
(using \x).  The default value is 35.

nroff  If this is non-zero, then ndefine behaves like define and tdefine is ignored, otherwise tdefine behaves like define and  nde-
fine  is  ignored.  The default value is 0 (This is typically changed to 1 by the eqnrc file for the ascii, latin1, utf8, and
cp1047 devices.)

A more precise description of the role of many of these parameters can be found in Appendix H of The TeXbook.

Macros
Macros can take arguments.  In a macro body, \$n where n is between 1 and 9, is replaced by the n-th 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.

FILES
/usr/share/groff/1.22.2/tmac/eqnrc  Initialization file.

MATHML MODE LIMITATIONS
MathML  is  designed  on the assumption that it cannot know the exact physical characteristics of the media and devices on which it will be
rendered.  It does not support fine control of motions and sizes to the same degree troff does.	Thus:

*      eqn parameters have no effect on the generated MathML.

*      The special, up, down, fwd, and back operations cannot be implemented, and yield a MathML <merror>' message instead.

*      The vcenter keyword is silently ignored, as centering on the math axis is the MathML default.

*      Characters that eqn over troff sets extra large - notably the integral sign - may appear too small and need to have their <mstyle>'

As  in  its troff mode, eqn in MathML mode leaves the .EQ and .EN delimiters in place for displayed equations, but emits no explicit delim-
iters around inline equations.  They can, however, be recognized as strings that begin with $' and end with $'  and  do  not
cross line boundaries.

See the BUGS section for translation limits specific to eqn.

BUGS
Inline equations are set at the point size that is current at the beginning of the input line.

In MathML mode, the mark and lineup features don't work.  These could, in theory, be implemented with <maligngroup>' elements.

In  MathML mode, each digit of a numeric literal gets a separate <mn></mn>' pair, and decimal points are tagged with <mo></mo>'.  This is
allowed by the specification, but inefficient.

Groff Version 1.22.2						  7 February 2013							    EQN(1)`