Single parameter representation for the PBE (upper panel) and SOGGA11 (lower panel) GGA exchange functionals as a function of the reduced density variables \(u\), eq. \ref{eqn:4} (left plots) and \(s\), eq. \ref{eqn:3} (right plots). For both functionals, the black dots are the decoded points, the orange solid curve is the original enhancement factor as obtained directly from LibXC, and the dashed red curve is the result of the decoding of the single parameter and the interpolation via univariate cubic spline. Results are obtained with \(N=100\)  points and \(\beta=12\). A Jupyter notebook to encode every GGA exchange functional in LibXC, as well as to reproduce the plots and to calculate the encoding and interpolation errors is associated with the Figure.