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- .SC "Shorthand for In-line Equations"
- .PP
- In a mathematical document,
- it is necessary to follow mathematical conventions
- not just in display equations,
- but also in the body of the text,
- for example by making variable names like $x$ italic.
- Although this could be done by surrounding the appropriate parts
- with
- .UC .EQ
- and
- .UC .EN ,
- the continual repetition of
- .UC .EQ
- and
- .UC .EN
- is a nuisance.
- Furthermore, with `\(mims',
- .UC .EQ
- and
- .UC .EN
- imply a displayed equation.
- .PP
- .UC EQN
- provides a shorthand for short in-line expressions.
- You can define two characters to mark the left and right ends
- of an in-line equation, and then type expressions right in the middle of text
- lines.
- To set both the left and right characters to dollar signs, for example,
- add to the beginning of your document the three lines
- .P1
- .EQ
- delim %%
- .EN
- .P2
- Having done this, you can then say things like
- .P1
- .fi
- Let %alpha sub i% be the primary variable,
- and let %beta% be zero.
- Then we can show that %x sub 1% is %>=0%.
- .P2
- This works as
- you might expect _
- spaces, newlines, and so on are significant
- in the text, but not in the equation part itself.
- Multiple equations can occur in a single input line.
- .PP
- Enough room is left before and after a line that contains
- in-line expressions
- that something like
- $sum from i=1 to n x sub i$
- does not interfere with the lines surrounding it.
- .PP
- To turn off the delimiters,
- .P1
- .EQ
- delim off
- .EN
- .P2
- Warning: don't use braces, tildes, circumflexes, or double quotes as delimiters _
- chaos will result.
- .SC "Definitions"
- .PP
- .UC EQN
- provides a facility so you can give
- a frequently-used string of characters a name,
- and thereafter just type the name instead of the
- whole string.
- For example, if the sequence
- .P1
- x sub i sub 1 + y sub i sub 1
- .P2
- appears repeatedly throughout a paper,
- you can save re-typing it each time by defining it like this:
- .P1 2
- define xy 'x sub i sub 1 + y sub i sub 1'
- .P2
- This makes
- .ul
- xy
- a shorthand for whatever characters occur between the single quotes
- in the definition.
- You can use any character instead of quote to mark the ends of the definition,
- so long as it doesn't appear inside the definition.
- .PP
- Now you can use
- .ul
- xy
- like this:
- .P1
- ^EQ
- f(x) = xy ...
- ^EN
- .P2
- and so on.
- Each occurrence of
- .ul
- xy
- will expand into what it was defined as.
- Be careful to leave spaces or their equivalent
- around the name
- when you actually use it, so
- .UC EQN
- will be able to identify it as special.
- .PP
- There are several things to watch out for.
- First, although definitions can use previous definitions,
- as in
- .P1
- .EQ
- define xi ' x sub i '
- define xi1 ' xi sub 1 '
- .EN
- .P2
- .ul
- don't define something in terms of itself'
- A favorite error is to say
- .P1
- define X ' roman X '
- .P2
- This is a guaranteed disaster,
- since X
- .ul
- is
- now defined in terms of itself.
- If you say
- .P1
- define X ' roman "X" '
- .P2
- however, the quotes
- protect the second X,
- and everything works fine.
- .PP
- .UC EQN
- keywords can be redefined.
- You can make
- / mean
- .ul
- over
- by saying
- .P1
- define / ' over '
- .P2
- or redefine
- .ul
- over
- as /
- with
- .P1
- define over ' / '
- .P2
- .PP
- If you need different things
- to print on a terminal and on the typesetter, it is sometimes worth
- defining a symbol differently in
- .UC NEQN
- and
- .UC EQN .
- This can be done with
- .ul
- ndefine
- and
- .ul
- tdefine.
- A definition made with
- .ul
- ndefine
- only takes effect if you are running
- .UC NEQN ;
- if you use
- .ul
- tdefine,
- the definition only applies for
- .UC EQN .
- Names defined with plain
- .ul
- define
- apply to both
- .UC EQN
- and
- .UC NEQN .
- .SC "Local Motions"
- .PP
- Although
- .UC EQN
- tries to get most things at the right place on the paper,
- it isn't perfect, and occasionally you will need to tune
- the output to make it just right.
- Small extra horizontal spaces can be obtained with
- tilde and circumflex.
- You can also say
- .ul
- back n
- and
- .ul
- fwd n
- to move small amounts horizontally.
- .ul
- n
- is how far to move in 1/100's of an em (an em is about the width
- of the letter
- `m'.)
- Thus
- .ul
- back 50
- moves back about half the width of an m.
- Similarly you can move things up or down with
- .ul
- up n
- and
- .ul
- down n.
- As with
- .ul
- sub
- or
- .ul
- sup,
- the local motions affect the next thing in the input,
- and this can be something arbitrarily complicated if it is enclosed
- in braces.
-