composite_u_matrix: Matrix formula to estimate the u ratio of a composite variable

Description

This function estimates the u ratio of a composite variable when at least one matrix of correlations (restricted or unrestricted) among the variables is available.

where \(u_{composite}\) is the composite u ratio, \(\mathbf{u}\) is a vector of u ratios, \(\mathbf{R}_{i}\) is a range-restricted correlation matrix, \(\mathbf{R}_{a}\) is an unrestricted correlation matrix, and \(\mathbf{w}\) is a vector of weights.