And so for this overdetermined case we use dgelss.f90 from the MKL library. The routine uses singular value decomposition to obtain the linear coefficients A flowchart outlining MSA is given below. A short video demonstrating the MSA software to generate a PIPs basis and a fit to a sample dataset of H 3 O - 2 energies and gradients is available to the interested reader. We emphasize that the output of MSA is the full PIPs basis and, if fitting, a potential routine that produces energies and gradients (if desired)