usage: s = boxplot (data,notched,symbol,vertical,maxwhisker);

The box plot is a graphical display that simultaneously describes several
important features of a data set, such as center, spread, departure from
symmetry, and identification of observations that lie unusually far from
the bulk of the data.

data is a matrix with one column for each dataset, or data is a cell
vector with one cell for each dataset.
notched = 1 produces a notched-box plot. Notches represent a robust
estimate of the uncertainty about the median.
notched = 0 (default) produces a rectangular box plot.
notched in (0,1) produces a notch of the specified depth.
notched values outside [0,1] are amusing if not exactly practical.
symbol sets the symbol for the outlier values, default symbol for
points that lie outside 3 times the interquartile range is 'o',
default symbol for points between 1.5 and 3 times the interquartile
range is '+'.
Exaples
symbol = '.' points between 1.5 and 3 times the IQR is marked with
'.' and points outside 3 times IQR with 'o'.
symbol = ['x','*'] points between 1.5 and 3 times the IQR is marked with
'x' and points outside 3 times IQR with '*'.
vertical = 0 makes the boxes horizontal, by default vertical = 1.
maxwhisker defines the length of the whiskers as a function of the IQR
(default = 1.5). If maxwhisker = 0 then boxplot displays all data
values outside the box using the plotting symbol for points that lie
outside 3 times the IQR.

The returned matrix s has one column for each dataset as follows:

1  minimum
2  1st quartile
3  2nd quartile (median)
4  3rd quartile
5  maximum
6  lower confidence limit for median
7  upper confidence limit for median

Example

title("Grade 3 heights");
tics("x",1:2,["girls";"boys"]);
axis([0,3]);
boxplot({randn(10,1)*5+140, randn(13,1)*8+135});