Dear Hartig,
Thanks for your reply. I am sorry for my poor knowledge in statistics.
But I wonder why the definition of 'linearity' of statistics is different
from that of engineering mathematics, which defines 'linear' as:
Each unknown xj appears to the first power only, and that there are no
cross product terms xi*xj with i!=j.
Wen-Feng
In article <[EMAIL PROTECTED]>,
[EMAIL PROTECTED] says...
> Generally, you can include an interaction (or moderator) term in a linear
> model, like
> y = b0 + b1 * x1 + b2 * x2 + b3 * x1*x2,
> and the model still is linear. If you decide not to include x1 and x2, like
> y = b0 + b1 * x1*x2,
> you still have a linear model.
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