For a list of matrices \(\{ X^{(1)}, \dots, X^{(L)} \}\), all of the same dimension, this function computes the matrix \(\hat{X}\) with \(i,j\) entry \( \hat{X}_{i,j} = \) quantile(\( \{ X_{ i,j }^{(l)} \}_{l=1}^L \), q). This function does not run any check on the dimensions and uses OpenMP if available. This is only a convenience function that is supposed to speed up quantile computation for very large problems. The results may be slightly different from R's quantile which should be used for small problems.