eqn(1) — Linux manual page

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eqn(1)                   General Commands Manual                  eqn(1)

Name         top

       eqn - format equations for groff or MathML

Synopsis         top

       eqn [-rCNR] [-d xy] [-f F] [-m n] [-M dir] [-p n] [-s n] [-T
           name] [file ...]

       eqn --help

       eqn -v
       eqn --version

Description         top

       The GNU implemenation of eqn is part of the groff(7) document
       formatting system.  eqn is a troff(1) preprocessor that
       translates descriptions of equations embedded in roff(7) input
       files into the language understood by troff(1).  It copies the
       contents of each file to the standard output stream, except that
       lines between .EQ and .EN (or “inline” within a pair of user-
       specified delimiters) are interpreted as equation descriptions.
       Normally, eqn is not executed directly by the user, but invoked
       by specifying the -e option to groff(1).  While GNU eqn's input
       syntax is highly compatible with AT&T eqn, the output eqn
       produces cannot be processed by AT&T troff; GNU troff (or a troff
       implementing relevant GNU extensions) must be used.  If no file
       operands are given on the command line, or if file is “-”, the
       standard input stream is read.

       Unless the -R option is given, eqn searches for the file eqnrc in
       the directories given with the -M option first, then in /usr/
       local/lib/groff/site-tmac, /usr/local/share/groff/site-tmac, and
       finally in the standard macro directory /usr/local/share/groff/
       1.23.0/tmac.  If it exists, eqn processes it before the other
       input files.

       Only the differences between GNU eqn and AT&T eqn are described
       in this document.  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.

       Three points are worth special note.

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

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

       •      GNU eqn sets the input token “...” as three periods or low
              dots, rather than the three centered dots of AT&T eqn.  To
              get three centered dots, write cdots or “cdot cdot cdot”.

   Controlling delimiters
       If not in compatibility mode, eqn recognizes
              delim on
       as a command 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.

              ordinary      an ordinary character such as “1” or “x”
              operator      a large operator such as “Σ”
              binary        a binary operator such as “+”
              relation      a relation such as “=”
              opening       an opening bracket such as “(”
              closing       a closing bracket such as “)”
              punctuation   a punctuation character such as “,”
              inner         a sub-formula contained within brackets
              suppress      a type without 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 follows.

                     type "binary" \(mu

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

       chartype t text
              Each (unquoted) character in text is assigned type t.  The
              type t can also be “letter” or “digit”; in these cases
              chartype changes the font style of the characters.  See
              subsection “Fonts” below.  For example,

                     chartype "punctuation" .,;:

              assigns the “punctuation” type to each of the characters
              in “.,;:” wherever they subsequently appear in an

   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

                     <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; it is also the vertical
              position used for fraction bars.  For example, sum is
              defined as follows.

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

              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 follows.

                     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

       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 neutral apostrophe (') that is not the
              first character on the input line 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 indicates how much a subscript on that object
              should be “tucked in”, or placed to the left relative to a
              non-subscripted glyph of the same size.  The skew of an
              object is how far to the right of the center of the object
              an accent over it 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.

                     define cancel 'special Ca'
                     .de Ca
                     .  ds 0s \
                     \D'l \\n(0wu -\\n(0hu-\\n(0du'\

              You could then cancel an expression e with “cancel { e }”.

              Here's a more complicated construct that draws a box
              around an expression.

                     define box 'special Bx'
                     .de Bx
                     .ds 0s \
                     \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'\
                     .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 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.

       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, where 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

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

                     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; fat text uses
                            <mstyle mathvariant='double-struck'>

                     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.

                     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.

                     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.

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

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

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

                     This amount of space is automatically inserted
                     after punctuation characters.

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

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

                     The height of lowercase letters without ascenders
                     such as “x”.

                     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

                     This should be 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

              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

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

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

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

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

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

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

                     This much vertical space is added above and below

                     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.

                     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.

                     This much space is added between columns in a

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

                     If this is non-zero, lines are drawn using the \D
                     escape sequence, rather than with the \l escape
                     sequence and the \[ru] character.

                     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.

                     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 ndefine is ignored.  The
                     default value is 0.  (This is typically changed
                     to 1 by the eqnrc file for the ascii, latin1, utf8,
                     and cp1047 drivers.)

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

       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

       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

       ifdef name X anything X
              If name has been defined by define (or has been
              automatically defined because name is the output driver)
              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 baseline), and

       eqn normally uses at least two fonts to set an equation: an
       italic font for letters, and a roman font for everything else.
       The AT&T eqn 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

Options         top

       --help displays a usage message, while -v and --version show
       version information; all exit afterward.

       -C     Recognize .EQ and .EN even when followed by a character
              other than space or newline, and do not handle the “delim
              on” statement specially.

       -d xy  Specify delimiters x and y for the left and right ends,
              respectively, of inline equations.  Any delim statements
              in the source file override this.

       -f F   This is equivalent to a “gfont F” command.

       -m n   Set the minimum point size to n.  eqn will not reduce the
              size of subscripts or superscripts to a smaller size
              than n.

       -M dir Search dir for eqnrc before the default directories.

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

       -p n   This says that subscripts and superscripts should be
              n points smaller than the surrounding text.  This option
              is deprecated.  Normally, eqn sets subscripts and
              superscripts at 70% of the size of the surrounding text.

       -r     Only one size reduction.

       -R     Don't load eqnrc.

       -s n   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.

       -T name
              The output is for output driver 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 driver.  However, if the specified driver
              is “MathML”, the output is MathML markup rather than troff
              commands, and eqnrc is not loaded at all.  The default
              output driver is ps.

Files         top

              Initialization file.

MathML mode limitations         top

       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

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

       •      Characters that eqn sets extra large in troff mode—notably
              the integral sign—may appear too small and need to have
              their “<mstyle>” wrappers adjusted by hand.

       As in its troff mode, eqn in MathML mode leaves the .EQ and .EN
       delimiters in place for displayed equations, but emits no
       explicit delimiters around inline equations.  They can, however,
       be recognized as strings that begin with “<math>” and end with
       “</math>” and do not cross line boundaries.

       See section “Bugs” below for translation limits specific to eqn.

Bugs         top

       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.

See also         top

       “Typesetting Mathematics—User's Guide” (2nd edition), by Brian W.
       Kernighan and Lorinda L. Cherry, 1978, AT&T Bell Laboratories
       Computing Science Technical Report No. 17.

       The TeXbook, by Donald E. Knuth, 1984, Addison-Wesley

       groff_char(7), particularly subsections “Logical symbols”,
       “Mathematical symbols”, and “Greek glyphs”, documents a variety
       of special character escapes useful in mathematical typesetting.

       groff(1), troff(1), pic(1), groff_font(5)

COLOPHON         top

       This page is part of the groff (GNU troff) project.  Information
       about the project can be found at 
       ⟨http://www.gnu.org/software/groff/⟩.  If you have a bug report
       for this manual page, see ⟨http://www.gnu.org/software/groff/⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://git.savannah.gnu.org/git/groff.git⟩ on 2021-08-27.  (At
       that time, the date of the most recent commit that was found in
       the repository was 2021-08-23.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

groff 1.23.0.rc1.654-4e1db-dir1t9yAugust 2021                       eqn(1)

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