how set up regression for interaction?

[Guest]

I know how to do multiple regression in Excel. But when you want regerssion
with interaction between two variable, how do you set up the spreadsheet. Do
you cerate a thrid variable by multiplying the two variables or is there a
function in excel for specifying interaction? Same for setting up quadratic
terms.

 

[Guest]

Polynomials of one variable can be specified via an array formula; for example
=LINEST(y,x^{1,2,3})
would fit a cubic. I do not immediately see a simple way to constuct an
array formula that would take multiple columns and return not only those
columns but products of them as well.

It would be possible to write such a function in VBA.

Jerry