Linked Tour Menu

When two or more XGobi's are initiated, with the same data or the same number
of variables they can be linked during tour mode. The default state is
"Unlink". For linking to begin one XGobi needs to be set to "Send" and the
other(s) to "Receive". The projection coefficients of the sending XGobi are
broadcast to the other XGobi's so that each displays identical projections.

There are various types of analyses where this facility is
envisioned as useful. One is to look at identical projections of
two different but comparable data sets; for example, one data set
could be randomly split in two for cross-validation purposes.
Another is to compare two different projection pursuit indices on
the same data set.

When the sending XGobi is showing sphered data, two sets of
projection coefficients are sent, a set appropriate to the sphered
data space and the other being the first set back-transformed
through the sphering transformation to give the projection
coefficients appropriate to the unsphered data space. If the
receiving XGobi is displaying sphered data it will use the first
set of projection coefficients, however if it is showing the
unsphered data it will use the second set. The latter case is
useful for displaying projection pursuit in the unsphered data
space as it is proceeding in the sending XGobi.  (The variable bars
may go out of the circle in the receiving XGobi, which looks a bit
strange but is quite normal.)

There are some potential pitfalls! For example, if the sending
XGobi is showing the raw data and the receiving XGobi is showing
sphered data, then linking doesn't make much sense and a warning
message is displayed.  It also doesn't make sense to do linked
touring when two XGobis display different data sets which are
sphered, unless the sphering has been done identically on each;
however, the program doesn't detect this case.