It does so by evaluating each PIP over the range of Morse variables for a given data set and simply rank-ordering them by magnitude. (The observant reader will note that at large internuclear distances the corresponding Morse variables are very small. These general occur at the "fringes" of the dataset, so those PIPs can be safely ignored. (This observation is also central to the "fragmented basis" approach for large molecules described below.) Also, noting that the product of two PIPs is also a PIP there is an option to increase the PIPs basis by using this simple fact. (This is not often done by us.) Finally and significantly, the techniques of fast reverse differentiation (from backpropagation techniques in neural networks) is developed using complex Matheatica script that ulimately creates Fortran 90 software to do this.