kinetic energy of noninteracting fermions in 1D, mean absolute errors below 1 kcal/mol on
test densities similar to the training set are reached with fewer than 100 training densities. A
predictor identifies if a test density is within the interpolation region. Via principal component
analysis, a projected functional derivative finds highly accurate self-consistent densities. The
challenges for application of our method to real electronic structure problems are discussed.