Upper plot: variation of the reconstruction error for the SEM with the embedding dimension D. For each embedding dimension, the number K of modes that minimises the error is chosen. Bottom plot: comparison between the measured flux from the SEM (dashed line) and the flux reconstructed with an embedding dimension of D = 4 (thick line), and D = 15 (thin line). The Mg ii index is shown for comparison (filled curve), with arbitrary units.