\shortstackSynopsis:
\shortstack[position]{line 1 \\ ... }
Produce a vertical stack of objects.
This labels the y axis.
\put(0,0){\vector(1,0){4}} % x axis
\put(0,0){\vector(0,1){2}} % y
\put(-0.25,2){\makebox[0][r]{\shortstack[r]{$y$\\ axis}}}
For a short stack, the reference point is the lower left of the stack. In the above example the \mbox & \makebox puts the stack flush right in a zero width box so in total the short stack sits slightly to the left of the y axis.
The valid positions are:
rMake objects flush right
lMake objects flush left
cCenter objects (default)
Separate objects into lines with \\. These stacks are short in
that, unlike in a tabular or array environment, here the
rows are not spaced out to be of even heights. Thus, in
\shortstack{X\\o\\o\\X} the first and last rows are taller than
the middle two. You can adjust row heights either by putting in the
usual interline spacing with \shortstack{X\\ \strut o\\o\\X},
or by hand, via an explicit zero-width box \shortstack{X \\
\rule{0pt}{12pt} o\\o\\X} or by using \\’s optional
argument \shortstack{X\\[2pt] o\\o\\X}.
The \shortstack command is also available outside the
picture environment.