Helper function for building multivariate scglr formula.
NOTE: Interactions involving factors are not allowed for now.
For interactions between two quantitative variables, use I(x*y) as usual.
multivariateFormula(namesY, namesX, namesAX = NULL)a vector of character containing the names of the dependent variables.
a vector of character containing the names of the covariates (X) involved in the components.
a vector of character containing the names of the additional covariates.
an object of class Formula.