Estimates the weights associated with the functional coefficients
\(\alpha_l(x)\) using the using Ordinary Least Squares.
The problem can be formulated as:
$$A(x) = \displaystyle \sum_{l=1}^{L} y_l \alpha_l(x)$$
where \(A(x)\) is the aggregated function evaluated at each point \(x\),
\(\alpha_l(x)\) are the functional coefficients, and \(y_l\) are the weights to be estimated.