Function getAmatrix finds A-matrices used to express ANOVA sum of squares as quadratic forms in \(y\).
getAmatrix(X1, X2)(matrix) lower order model matrix (comprising all factors entering model before 'X2'-factor)
(matrix) higher order model matrix (entering model after 'X1' factors)
(matrix) for obtaining quadratic forms in \(y\) expression ANOVA sum of squares
Compute A-Matrix for expressing ANOVA Type-1 sequential sum of squares \(m_{SS}\) as quadratic form in \(y\) (column vector of observations), \(y^{T}Ay = m_{SS}\). In random models, when the intercept is the only fixed effect, the design matrix of fixed effects is equal to a column vector where each element is equal to one (1). In this setting, it holds \(1^{T}A1 = 0\), i.e. all elements of A summing to zero.
This function is not intended to be used directly.