The array environment, like the tabular
environment, produces a box
consisting of a sequence of rows of
vertically aligned columns. It can be used only within the
math environment.
There is a single mandatory argument describing the number of columns and
the alignment within each of them.
Each of the v's in the argument specifies a column and may be
a l, c, or r indicating that the column should
be flush left, centered, or flush right, respectively. For more
complex options, see the tabular environment
which uses the same format.
The optional pos argument specifies the alignment of the array with
its surrounding environment (recall that LaTeX treats boxes as one,
albeit large letter). The options are
t - align on top row
b - align on bottom row
The default is to align on the center of the array.
Column entries must be separated by an &. Column entries
may include other LaTeX commands, even other arrays.
Each row of the array must be terminated with
the string \\.
Note that there is no & after the last
item in a row and no \\ after the last row. (An exception is if
an \hline is used to place a line
at the bottom; it follows a \\.)
Each item in the array is treated as if it were surrounded by braces. Thus,
a declaration within an array item is
local to that item, i.e., it is ended by an & or \\.
Horizontal and vertical lines in the array are produced with