[R] Tukey's one degree of freedom for nonadditivity?

[Spencer Graves]

	  Is there code available to decompose interactions involving at least 
one nominal factor with more than 2 levels as described, e.g., by Tukey 
or by Mandel (1971, Technometrics, 13: 1-18)?

	  Tukey's model:

	E(y[i,j]) = mu0 + a[i] + b[j] + c*a[i]*b[j],

estimating a, b, and c so sum(a) = sum(b)= 0.  Mandel essentially 
describes a singular value decomposition of the interaction.

Thanks,
Spencer Graves