Chicken feed mixture
[1] Design points
[2] Maize, X1
[3] Fishmeal, X2
[4] Soy been, X3
[5] Mean final weight, Y
G.S.Wewala (1980) analyzed a mixture experiment in which chickens
were fed a mixture of maize, fisheal and soy bean and their weight
noted when 1 000 days old. At ech of ten design points, 32 chickens
were reared giving the results. 
As proportions add to one, only terms in the first two ingredients
were included in the model which was a full quadratic in these two
ingredients, namely
     y = b1.X1 + b2.X2 + b3.X1^2 + b4.X1.X2 + b5.X2^2 + e.
Estimate ridge traces of the coefficient estimates and the variance
inflation factors for some ridge coefficients "k".