We now describe the machine learning classification (MLC) approaches we use to predict zero matrix elements. This is a standard 0/1 classification problem: in the training set, elements with a magnitude greater than the threshold are labelled 1, and elements with smaller magnitudes are labelled 0. The ML model then will predict 0 or 1 for an unknown matrix element; if it predicts 0, the matrix element can be set to zero so the computation can be skipped, and otherwise if the prediction is 1, the actual value matrix element will be calculated.