Short Math Guide for L
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T
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X, version 1.09 (2002-03-22) 11
\bigl( \begin{smallmatrix}
a&b\\ c&d
\end{smallmatrix} \bigr)
To produce a row of dots in a matrix spanning a given number of columns, use \hdotsfor.
For example, \hdotsfor{3} in the second column of a four-column matrix will print a row
of dots across the final three columns.
For piece-wise function definitions there is a cases environment:
P_{r-j}=\begin{cases}
0& \text{if $r-j$ is odd},\\
r!\,(-1)^{(r-j)/2}& \text{if $r-j$ is even}.
\end{cases}
Notice the use of \text and the embedded math.
Note. The plain T
E
X form \matrix{...\cr...\cr} and th e related commands \pmatrix, \cases should be
avoided in L
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X (and when the amsmath package is loaded th ey are disab led).
4.5. Math spacing commands When the amsmath package is used, all of these math
spacing commands can be used b oth in and out of math mode.
Abbrev. Spelled out Example Abbrev. Spelled out Example
no space 34 no space 34
\, \thinspace 34 \! \negthinspace 34
\: \medspace 34 \negmedspace 34
\; \thickspace 34 \negthickspace 34
\quad 34
\qquad 34
For finer control over math spacing, use \mspace and ‘math units’. One math unit, or mu,
is equal to 1/18 em. Thus to get a negative half \quad write \mspace{-9.0mu}.
There are also three commands that leave a space equal to the height and/or width of
a given fragment of L
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X material:
Example Result
\phantom{XXX} space as wide and high as three X’s
\hphantom{XXX} space as wide as three X’s; height 0
\vphantom{X} space of width 0, height = height of X
4.6. Dots For preferred placement of ellipsis dots (raised or on-line) in various contexts
there is no ge neral consensus. It may therefore be considered a matte r of taste. By using
the semantically oriented commands
• \dotsc for “dots with commas”
• \dotsb for “dots with binary operators/relations”
• \dotsm for “multiplication dots”
• \dotsi for “dots with integrals”
• \dotso for “other dots” (none of the above)
instead of \ldots and \cdots, you make it possible for your do c ument to be adapted to
different conventions on the fly, in case (for example) you have to submit it to a publisher
who insists on following house tradition in this respect. The default treatment for the
various kinds follows American Mathematical Society conventions:
We have the series $A_1,A_2,\dotsc$,
the regional sum $A_1+A_2+\dotsb$,
the orthogonal product $A_1A_2\dotsm$,
and the infinite integral
\[\int_{A_1}\int_{A_2}\dotsi\].
We have the series A
1
,A
2
,..., the re-
gional sum A
1
+ A
2
+ ···, the orthogonal
product A
1
A
2
···, and the infinite inte-
gral
A
1
A
2
···.