Compute the interaction part of the model.
compute_pliable(X, Z, theta)a vector of length N of the calculated interaction term for a single response
N by p matrix of predictors
N by K matrix of modifying variables. The elements of Z may represent quantitative or categorical variables, or a mixture of the two. Categorical variables should be coded by 0-1 dummy variables: for a k-level variable, one can use either k or k-1 dummy variables.
theta coefficients for a single response ncol(X) by ncol(Z)