What do you mean by “a linear combination of variables” when describing discriminant analysis?
Suppose x1, x2, x3, are independent variables: then a linear combination is simply any function y such that y = a + b1x1 + b2x1 + b1x1 where a, b1, b2, b3are constants. A discriminant function is a linear combination of variables, as just defined, such that the difference(s) of mean y values between 2 or more groups is maximised: i.e. the function discriminates maximally between the 2 (or more) groups.
