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interactplot(y,a [,b,c ...] [graphics keywords]), y a REAL vector, a, b,
  c, ... vectors of positive integers the same length as y.
interactplot(means [graphics keywords]), means a REAL matrix or array.

Keywords: factorial, plots
interactplot(y,a [,b,c ...] [graphics keywords]) makes an interaction
plot of the marginal means of REAL vector y for all combinations of
variables a, b, c, ....  The variables a, b, ... must be vectors of
positive integers the same length as y.

The levels of variable a will be put on the horizontal axis and separate
lines drawn for each combination of variables values of b, c, ....  When
a is the only factor argument, only one line is drawn.  Lines are
numbered 1, 2, 3, ... with the levels of b varying fastest, c varying
more slowly, etc.

interactplot(means [graphics keywords]) where means is a REAL matrix or
array will make an interaction plot with the first dimension of means on
the horizontal axis, and separate lines for each combination of the
other dimensions.  The lines are numbered 1, 2, 3, ...  with the last
dimension varying slowest.  interactplot(tabs(y,a,b,means:T)) makes the
same plot as interactplot(y,a,b).

In both usages, any graphics keywords will be passed to function
chplot() which actually makes the plot.  In particular, for example,

  Cmd> interactplot(y,a,b,symbols:vector("B1","B2","B3"),\

will label the curves B1, B2 and B3 instead of 1, 2 and 3 and the
horizontal axis location A1, A2, A3 and A4.

Gary Oehlert 2003-01-15