---
name: "eqn"
section: "1"
platform: "linux"
package: "groff"
version: "1.24.2-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/eqn"
---

# eqn(1)

format mathematics (equations) for groff or MathML

## Name

eqn - format mathematics (equations) for *groff* or MathML

## Synopsis

**eqn** \[**-CNrR**\] \[**-**d  *xy*\] \[**-f**  *global-italic-font*\] \[**-m**  *minimum-type-size*\] \[**-M**  *eqnrc-directory*\] \[**-p**  *super/subscript-size-reduction*\] \[**-s**  *global-type-size*\] \[**-T**  *device*\] \[*file* ...\]

**eqn** **--help**

**eqn** **-v**

**eqn** **--version**

## Description

The GNU implementation of *eqn* is part of the [*groff*(7)](/groff/7.md) document formatting system. *eqn* is a [*troff*(1)](/troff/1.md) preprocessor that translates expressions in its own language, embedded in [*roff*(7)](/roff/7.md) input, into mathematical notation typeset by [*troff*(1)](/troff/1.md). It copies each *file*'s contents to the standard output stream, translating each *equation* between lines starting with **.EQ** and **.EN**, or within a pair of user-specified delimiters. Normally, *eqn* is not executed directly by the user, but invoked by specifying the **-e** option to [*groff*(1)](/groff/1.md). 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 present, or if *file* is “**-**”, *eqn* reads the standard input stream.

Unless the **-R** option is used, *eqn* searches for the file *eqnrc* in the directories given with the **-M** option first, then in */usr/share/groff/site-tmac*, and finally in the standard macro directory */usr/share/groff/1.24.2/tmac*. If it exists and is readable, *eqn* processes it before any input.

This man page primarily discusses the differences between GNU *eqn* and AT&T *eqn*. 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. Four points are worth note.

- •

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

- •

  GNU *eqn* does not support terminal devices well, though it may suffice for simple inputs.

- •

  GNU *eqn* sets the input token “**...**” as an ellipsis on the text baseline, not the three centered dots of AT&T *eqn*. Set an ellipsis on the math axis with the GNU extension macro **cdots**.

- •

  GNU *eqn*'s **delim** primitive does not treat an “**on**” argument as a pair of equation delimiters.

### Anatomy of an equation

*eqn* input consists of tokens. Consider a form of Newton's second law of motion for constant mass. The input

```
.EQ
F =
m a
.EN
```

becomes F = m a. Each of **F**, **=**, **m**, and **a** is a token. Spaces and newlines are interchangeable; they separate tokens but do not break lines or produce space in the output.

Beyond their primary functions, the following input characters separate tokens as well.

- **{ }**

  Braces perform grouping. Whereas “**e sup a b**” expresses “(*e* to the *a*) times *b*”, “**e sup { a b }**” means “*e* to the (*a* times *b*)”. When immediately preceded by a “**left**” or “**right**” primitive, a brace loses its special meaning.

- **^ ~**

  are the *half space* and *full space,* respectively. Use them to tune the appearance of the output.

Tab and leader characters separate tokens as well as advancing the drawing position to the next tab stop, but are seldom used in *eqn* input. When they occur, they must appear at the outermost lexical scope. This roughly means that they can't appear within braces that are necessary to disambiguate the input; *eqn* will diagnose an error in this event. (See subsection “Macros” below for additional token separation rules.)

Other tokens are primitives, macros, an argument to either of the foregoing, or components of an equation.\

*Primitives* are fundamental keywords of the *eqn* language. They can configure an aspect of the preprocessor's state, as when setting a “global” font selection or type size (**gifont** and **gsize**), or declaring or deleting macros (“**define**” and **undef**); these are termed *commands.* Other primitives perform formatting operations on the tokens around them (as with **fat**, **over**, **sqrt**, or **up**).

Equation *components* include mathematical variables, constants, numeric literals, and operators. *eqn* remaps some input character sequences to *groff* special character escape sequences for economy in equation entry and to ensure that glyphs from an unstyled font are used; see [*groff\_char*(7)](/groff_char/7.md).

| | | | | |
| --- | --- | --- | --- | --- |
| `+` | `\[pl]` |  | `'` | `\[fm]` |
| `-` | `\[mi]` |  | `<=` | `\[<=]` |
| `=` | `\[eq]` |  | `>=` | `\[>=]` |

*Macros* permit primitives, components, and other macros to be collected and used together as a single token. Predefined macros make convenient the preparation of *eqn* input in a form resembling its spoken expression; for example, consider **cos**, **hat**, **inf**, and **lim**.

### Spacing and typeface

GNU *eqn* imputes a type to each equation component, adjusting the space around it accordingly. Recognized types follow; most affect spacing only, whereas the “**letter**” subtype of “**ordinary**” also assigns a style.

| | |
| --- | --- |
| `ordinary` | character such as “1”, “a”, or “!” |
| `letter` | character to be italicized by default |
| `digit` | *n/a* |
| `operator` | large operator such as |
| `binary` | binary operator such as “+” |
| `relation` | relational operator such as “=” |
| `opening` | opening bracket such as “(” |
| `closing` | closing bracket such as “)” |
| `punctuation` | punctuation character such as “,” |
| `inner` | sub-formula contained within brackets |
| `suppress` | component to which automatic spacing is not applied |

Two primitives apply types to equation components.

- **type** *t e*

  Apply type *t* to expression *e*.

- **chartype** *t text*

  Assign each character in (unquoted) *text* type *t*, persistently.

*eqn* sets up spacings and styles as if by the following commands.

| | |
| --- | --- |
| `chartype "letter"` | `abcdefghiklmnopqrstuvwxyz` |
| `chartype "letter"` | `ABCDEFGHIKLMNOPQRSTUVWXYZ` |
| `chartype "letter"` | `\[*a]\[*b]\[*g]\[*d]\[*e]\[*z]` |
| `chartype "letter"` | `\[*y]\[*h]\[*i]\[*k]\[*l]\[*m]` |
| `chartype "letter"` | `\[*n]\[*c]\[*o]\[*p]\[*r]\[*s]` |
| `chartype "letter"` | `\[*t]\[*u]\[*f]\[*x]\[*q]\[*w]` |
| `chartype "binary"` | `*\[pl]\[mi]` |
| `chartype "relation"` | `<>\[eq]\[<=]\[>=]` |
| `chartype "opening"` | `{([` |
| `chartype "closing"` | `})]` |
| `chartype "punctuation"` | `,;:.` |
| `chartype "suppress"` | `^~` |

*eqn* assigns all other ordinary and special *roff* characters, including numerals 0–9, the “**ordinary**” type. (The “**digit**” type is not used, but is available for customization.) In keeping with common practice in mathematical typesetting, lowercase, but not uppercase, Greek letters are assigned the “**letter**” type to style them in italics. The macros for producing ellipses, “**...**”, **cdots**, and **ldots**, use the “**inner**” type.

### Primitives

*eqn* supports without alteration the AT&T *eqn* primitives **above**, **back**, **bar**, **bold**, **define**, **down**, **fat**, **font**, **from**, **fwd**, **gfont**, **gsize**, **italic**, **left**, **lineup**, **mark**, **matrix**, **ndefine**, **over**, **right**, **roman**, **size**, **sqrt**, **sub**, **sup**, **tdefine**, **to**, **under**, and **up**.

### New primitives

We describe the GNU extension primitives “**type**” and **chartype** in subsection “Spacing and typeface” above; “**set**” and “**reset**” in subsection “Customization” below; and **gbfont**, **gifont**, and **grfont** in subsection “Fonts” below. In the following synopses, *X* can be any character not appearing in the parameter thus bracketed.

- *e1* **accent** *e2*

  Set *e2* as an accent over *e1*. *eqn* assumes that *e2* is at the appropriate height for a lowercase letter without an ascender, and shifts it vertically based on *e1*'s height. For example, *eqn* defines **hat** as follows.

  -

    ```
    accent { roman "^" }
    ```

-

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

- **big** *e*

  Enlarge the expression *e*; semantics like those of CSS “large” are intended. In *troff* output, the type size is increased by 5 scaled points. MathML output emits the following.

  -

    ```
    <mstyle mathsize='big'>
    ```

- **copy** *file* **include** *file*

  Interpolate the contents of *file*, omitting lines beginning with **.EQ** or **.EN**. *file* is sought relative to the current working directory.

- **ifdef** *name X anything X*

  If *name* is defined as a primitive or macro, interpret *anything*.

- **nosplit** *text*

  As "*text*", but since *text* is not quoted it is subject to macro expansion; it is not split up and the spacing between characters not adjusted per subsection “Spacing and typeface” above.

- *e* **opprime**

  As **prime**, but set the prime symbol as an operator on *e*. In the input “**A opprime sub 1**”, the “1” is tucked under the prime as a subscript to the “A” (as is conventional in mathematical typesetting), whereas when **prime** is used, the “1” is a subscript to the prime character. The precedence of **opprime** is the same as that of **bar** and “**under**”, and higher than that of other primitives except **accent** and **uaccent**. In unquoted text, a neutral apostrophe (**'**) that is not the first character on the input line is treated like **opprime**.

- **sdefine** *name X anything X*

  As “**define**”, but *name* is not recognized as a macro if called with arguments.

- *e1* **smallover** *e2*

  As **over**, but reduce the type size of *e1* and *e2*, and put less vertical space between *e1* and *e2* and the fraction bar. The **over** primitive corresponds to the TeX **\\over** primitive in displayed equation styles; **smallover** corresponds to **\\over** in non-display (“inline”) styles.\

- **space** *n*

  Set extra vertical spacing around the equation, replacing the default values, where *n* is an integer in hundredths of an em. If positive, *n* increases vertical spacing before the equation; if negative, it does so after the equation. This primitive provides an interface to *groff*'s **\\x** escape sequence, but with the opposite sign convention. It has no effect if the equation is part of a [*pic*(1)](/pic/1.md) picture.\

- **special** *troff-macro e*

  Construct an object by calling *troff-macro* on *e*. The *troff* string **0s** contains the *eqn* output for *e*, and the registers **0w**, **0h**, **0d**, **0skern**, and **0skew** the width, height, depth, subscript kern, and skew of *e*, respectively. (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, returns the drawing position to the text baseline at the beginning of *e*, and updates the foregoing registers to correspond to the new dimensions of the result.

-

  Suppose you want a construct that “cancels” an expression by drawing a diagonal line through it.\

  -

    ```
    .de Ca
    .  ds 0s \
    \Z'\\*(0s'\
    \v'\\n(0du'\
    \D'l \\n(0wu -\\n(0hu-\\n(0du'\
    \v'\\n(0hu'
    ..
    .EQ
    special Ca "x \[mi] 3 \[pl] x" ~ 3
    .EN
    ```

-

  We use the **\\\[mi\]** and **\\\[pl\]** special characters instead of + and - because they are part of the argument to a *troff* macro, so *eqn* does not transform them to mathematical glyphs for us. Here's a more complicated construct that draws a box around an expression; the bottom of the box rests on the text baseline. We define the *eqn* macro **box** to wrap the call of the *troff* macro **Bx**.\

  -

    ```
    .de Bx
    .ds 0s \
    \Z'\\h'1n'\\*[0s]'\
    \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
    ..
    .EQ
    define box ' special Bx $1 '
    box(foo) ~ "bar"
    .EN
    ```

- **split "***text***"**

  As *text*, but since *text* is quoted, it is not subject to macro expansion; it is split up and the spacing between characters adjusted per subsection “Spacing and typeface” above.

- *e1* **uaccent** *e2*

  Set *e2* as an accent under *e1*. *e2* is assumed to be at the appropriate height for a letter without a descender;  *eqn* vertically shifts it depending on whether *e1* has a descender. **utilde** is predefined using **uaccent** as a tilde accent below the baseline.

- **undef** *name*

  Remove definition of macro or primitive *name*, making it undefined.

- **vcenter** *e*

  Vertically center *e* about the *math axis*, a horizontal line upon which fraction bars and characters such as “+” and “−” are aligned. MathML already behaves this way, so *eqn* ignores this primitive when producing that output format. The built-in **sum** macro is defined as if by the following.

  -

    ```
    define sum ! { type "operator" vcenter size +5 \(*S } !
    ```

### Extended primitives

GNU *eqn* extends the syntax of some AT&T *eqn* primitives, introducing one deliberate incompatibility.

- **delim on**

  GNU *eqn* recognizes an “**on**” argument to the **delim** primitive specially, restoring any delimiters previously disabled with “**delim off**”. If delimiters haven't been specified, neither command has effect. Few *eqn* documents are expected to use “o” and “n” as left and right delimiters, respectively. If yours does, swap them, or select others.

- **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, uses the formatter's **\\x** escape sequence to increase the vertical spacing between rows; *eqn* ignores it when producing MathML. Negative values are accepted but have no effect. If more than one *n* occurs in a matrix or pile, the largest is used.

### Customization

When *eqn* generates *troff* input, the appearance of equations is controlled by a large number of parameters. They have no effect when generating MathML, which delegates typesetting to a MathML rendering engine. Configure these parameters with the “**set**” and “**reset**” primitives.

- **set** *p n*

  assigns parameter *p* the integer value *n*; *n* is interpreted in units of hundredths of an em unless otherwise stated. For example,

  ```
  set x_height 45
  ```

  says that *eqn* should assume that the font's x-height is 0.45 ems.

- **reset** *p*

  restores the default value of parameter *p.*

Available parameters *p* are as follows; defaults are shown in parentheses. We intend these descriptions to be expository rather than rigorous.

- **minimum\_size**

  sets a floor for the type size (in scaled points) at which equations are set (**5**).

- **fat\_offset**

  The **fat** primitive emboldens an equation by overprinting two copies of the equation horizontally offset by this amount (**4**). When producing MathML output, components to which **fat\_offset** applies instead use the following.

  ```
  <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 (**0**).

- **accent\_width**

  When **bar** or **under** is applied to a single character, the line is this long (**31**). 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 (**900**).

- **delimiter\_shortfall**

  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 (**50**).

- **null\_delimiter\_space**

  This much horizontal space is inserted on each side of a fraction (**12**).

- **script\_space**

  The width of subscripts and superscripts is increased by this amount (**5**).

- **thin\_space**

  This amount of space is automatically inserted after punctuation characters (**17**).

- **medium\_space**

  This amount of space is automatically inserted on either side of binary operators (**22**).

- **thick\_space**

  This amount of space is automatically inserted on either side of relations (**28**).

- **half\_space**

  configures the width of the space produced by the **^** token (**17**).

- **full\_space**

  configures the width of the space produced by the **~** token (**28**).

- **x\_height**

  The height of lowercase letters without ascenders such as “x” (**45**).

- **axis\_height**

  The height above the baseline of the center of characters such as “+” and “−” (**26**). It is important that this value is correct for the font you are using.

- **default\_rule\_thickness**

  This should be set to the thickness of the **\\\[ru\]** character, or the thickness of horizontal lines produced with the **\\D** escape sequence (**4**).

- **num1**

  The **over** primitive shifts up the numerator by at least this amount (**70**).

- **num2**

  The **smallover** primitive shifts up the numerator by at least this amount (**36**).

- **denom1**

  The **over** primitive shifts down the denominator by at least this amount (**70**).

- **denom2**

  The **smallover** primitive shifts down the denominator by at least this amount (**36**).

- **sup1**

  Normally superscripts are shifted up by at least this amount (**42**).

- **sup2**

  Superscripts within superscripts or upper limits or numerators of **smallover** fractions are shifted up by at least this amount (**37**). Conventionally, this is less than **sup1**.

- **sup3**

  Superscripts within denominators or square roots or subscripts or lower limits are shifted up by at least this amount (**28**). Conventionally, this is less than **sup2**.

- **sub1**

  Subscripts are normally shifted down by at least this amount (**20**).

- **sub2**

  When there is both a subscript and a superscript, the subscript is shifted down by at least this amount (**23**).

- **sup\_drop**

  The baseline of a superscript is no more than this much below the top of the object on which the superscript is set (**38**).

- **sub\_drop**

  The baseline of a subscript is at least this much below the bottom of the object on which the subscript is set (**5**).

- **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 (**11**).

- **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 (**17**).

- **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 (**20**).

- **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 (**60**).

- **big\_op\_spacing5**

  This much vertical space is added above and below limits (**10**).

- **baseline\_sep**

  The baselines of the rows in a pile or matrix are normally this far apart (**140**). Usually 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 (**26**). Usually equal to **axis\_height**.

- **column\_sep**

  This much space is added between columns in a matrix (**100**).

- **matrix\_side\_sep**

  This much space is added at each side of a matrix (**17**).\

- **draw\_lines**

  If non-zero, *eqn* draws lines using the *troff* **\\D** escape sequence, rather than the **\\l** escape sequence and the **\\\[ru\]** special character. The *eqnrc* file sets the default: **1** on **ps**, **html**, and the X11 devices, otherwise **0**.

- **body\_height**

  is the presumed height of an equation above the text baseline; *eqn* adds any excess as extra pre-vertical line spacing with *troff*'s **\\x** escape sequence (**85**).

- **body\_depth**

  is the presumed depth of an equation below the text baseline; *eqn* adds any excess as extra post-vertical line spacing with *troff*'s **\\x** escape sequence (**35**).

- **nroff**

  If non-zero, then **ndefine** behaves like **define** and **tdefine** is ignored, otherwise **tdefine** behaves like **define** and **ndefine** is ignored. The *eqnrc* file sets the default: **1** on **ascii**, **latin1**, and **utf8** devices, otherwise **0**.

### Macros

In GNU *eqn*, macros can take arguments. A word defined by any of the **define**, **ndefine**, or **tdefine** primitives followed immediately by a left parenthesis is treated as a *parameterized macro call:* subsequent tokens up to a matching right parenthesis are treated as comma-separated arguments. In this context only, commas and parentheses also serve as token separators. A macro argument is not terminated by a comma inside parentheses nested within it. In a macro definition, **$***n* , where *n* is between 1 and 9 inclusive, is replaced by the *n*th argument; if there are fewer than *n* arguments, it is replaced by nothing.

### Predefined macros

GNU *eqn* supports the predefined macros offered by AT&T *eqn*: **and**, **approx**, **arc**, **cos**, **cosh**, **del**, **det**, **dot**, **dotdot**, **dyad**, **exp**, **for**, **grad**, **half**, **hat**, **if**, **inter**, **Im**, **inf**, **int**, **lim**, **ln**, **log**, **max**, **min**, **nothing**, **partial**, **prime**, **prod**, **Re**, **sin**, **sinh**, **sum**, **tan**, **tanh**, **tilde**, **times**, **union**, **vec**, **==**, **!=**, **+=**, **-\>**, **\<-**, **\<\<**, **\>\>**, and “**...**”. The lowercase classical Greek letters are available as **alpha**, **beta**, **chi**, **delta**, **epsilon**, **eta**, **gamma**, **iota**, **kappa**, **lambda**, **mu**, **nu**, **omega**, **omicron**, **phi**, **pi**, **psi**, **rho**, **sigma**, **tau**, **theta**, **upsilon**, **xi**, and **zeta**. Spell them with an initial capital letter (**Alpha**) or in full capitals (**ALPHA**) to obtain uppercase forms.

GNU *eqn* further defines the macros **cdot**, **cdots**, and **utilde** (all discussed above), **dollar**, which sets a dollar sign, and **ldots**, which sets an ellipsis on the text baseline.

### Fonts

*eqn* uses up to three typefaces to set an equation: italic (oblique), roman (upright), and bold (heavy). Assign each a *groff* typeface with the GNU extension primitives **grfont**, **gifont**, and **gbfont.** The defaults are the styles **R**, **I**, and **B** (applied to the current font family). The **chartype** primitive (see above) sets a character's type, which determines the face used to set it. The “**letter**” type is set in italics; others are set in roman. Use the **bold** primitive to select an (upright) bold style.

- **gbfont** *f*

  Select *f* as the bold font.

- **gifont** *f*

  Select *f* as the italic font. GNU *eqn* recognizes **gfont** as a synonym for AT&T compatibility.

- **grfont** *f*

  Select *f* as the roman font.

### *roff* interface

The string **10** stores the most recently formatted equation. The register **MK** stores the horizontal drawing position of the most recently assigned mark. Avoid using these names for any other purpose.

GNU *eqn* internally employs register, string, macro, and diversion names beginning with the numeral **0**. (AT&T *eqn* used identifiers starting with the numeral **1**.) A document to be preprocessed with GNU *eqn* should not use any such identifiers.\

## Options

**--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.

- **-d** *xy*

  Specify delimiters *x* for left and *y* for right ends of equations not bracketed by **.EQ**/**.EN**. *x* and *y* need not be distinct. Any “**delim** *xy*” statements in the source file override this option.

- **-f** *F*

  is equivalent to “**gifont** *F*”.

- **-m** *n*

  is equivalent to “**set minimum\_size** *n*”.

- **-M** *dir*

  Search *dir* for *eqnrc* before those listed in section “Description” above.

- **-N**

  Prohibit newlines within delimiters, allowing *eqn* to recover better from missing closing delimiters.

- **-p** *n*

  Set sub- and superscripts *n* points smaller than the surrounding text. This option is deprecated. *eqn* normally sets sub- and superscripts at 70% of the type size of the surrounding text.

- **-r**

  Reduce the type size of super- and subscripts at most once relative to the base type size.

- **-R**

  Don't load *eqnrc*.

- **-s** *n*

  is equivalent to “**gsize** *n*”. This option is deprecated.

- **-T** *dev*

  Prepare output for the device *dev*. This option defines a macro *dev* with the value **1**; *eqnrc* thereby provides definitions appropriate to the device. However, if *dev* is “**MathML**”, *eqn* produces output in that language rather than *roff*, and does not load *eqnrc*. The default device is **ps**.

## Exit status

*eqn* exits with status **0** on successful operation, status **2** if the program cannot interpret its command-line arguments, and status **1** if it encounters an error during operation.

## Files

- */usr/share/groff/1.24.2/tmac/eqnrc*

  initializes the preprocessor for *troff* output. Any valid *eqn* input is accepted.

## MathML output limitations

MathML's design assumes that it cannot know the exact physical characteristics of the media and devices on which it will be rendered. It does not support control of motions and sizes to the same degree *troff* does.

- •

  GNU *eqn*'s rendering parameters (see section “Customization” above) have no effect on generated MathML.

- •

  The **special**, **up**, **down**, **fwd**, and **back** primitives cannot be implemented, and yield a MathML “\<merror\>” message instead.

- •

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

- •

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

As when producing *troff* output, *eqn* generates MathML that leaves the **.EQ** and **.EN** tokens in place, but emits nothing corresponding to **delim** delimiters. They can, however, be recognized as character sequences that begin with “\<math\>”, end with “\</math\>”, and do not cross line boundaries.

## Caveats

Tokens must be double-quoted in *eqn* input if they are not to be recognized as names of macros or primitives, or if they are to be interpreted by *troff*. In particular, short ones, like “**pi**” and “**PI**”, can collide with *troff* identifiers. For instance, the *eqn* command “**gifont PI**” does not select the [*gropdf*(1)](/gropdf/1.md) or [*grops*(1)](/grops/1.md) device's Palatino italic font as the global italic face; you must use “**gifont "PI"**” instead.

Delimited equations are set at the type size current at the beginning of the input line, not necessarily that immediately preceding the opening delimiter.

Unlike TeX, *eqn* does not inherently distinguish displayed and inline equation styles; see the **smallover** primitive above. However, macro packages frequently define **EQ** and **EN** macros such that the equation within is displayed. These macros may accept arguments permitting the equation to be labeled or captioned; see the package's documentation.

## Bugs

*eqn* abuses terminology—its “equations” can be inequalities, bare expressions, or unintelligible gibberish. But there's no changing it now.

When producing terminal output, GNU *eqn* renders lowercase Greek letters in roman instead of italic style.

When producing MathML output, the **mark** and **lineup** features don't work. These could, in theory, be implemented with “\<maligngroup\>” elements.

When producing MathML output, 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.

## Examples

We first illustrate *eqn* usage with a trigonometric identity.

```
.EQ
sin ( alpha + beta ) = sin alpha cos beta + cos alpha sin beta
.EN
```

It can be convenient to set up delimiters if mathematical content will appear frequently in running text.

```
.EQ
delim $$
.EN
Having cached a table of logarithms,
the property $ln ( x y ) = ln x + ln y$ sped calculations.
```

The quadratic formula affords an opportunity to use fractions, radicals, and the full space token **~**.

```
.EQ
x = { - b ~ \[+-] ~ sqrt { b sup 2 - 4 a c } } over { 2 a }
.EN
```

Alternatively, we could define the plus-minus sign as a binary operator. Automatic spacing puts 0.06 em less space on either side of the plus-minus than ~ does, this being the difference between the widths of the **medium\_space** parameter used by binary operators and that of the full space. Independently, we can define a macro “frac” for setting fractions.\

```
.EQ
chartype "binary" \[+-]
define frac ! { $1 } over { $2 } !
x = frac(- b \[+-] sqrt { b sup 2 - 4 a c }, 2 a)
.EN
```

## See also

“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 Professional. Appendix G discusses many of the parameters from section “Customization” above in greater detail.

[*groff\_char*(7)](/groff_char/7.md) documents a variety of special character escape sequences useful in mathematical typesetting. See subsections “Logical symbols”, “Mathematical symbols”, and “Greek glyphs” in particular.

[*groff*(1)](/groff/1.md), [*troff*(1)](/troff/1.md), [*pic*(1)](/pic/1.md), [*groff\_font*(5)](/groff_font/5.md)