Research Perspective Volume 16, Issue 17 pp 12108—12122

Figure 4. Eigensurfaces for early age medfly activity data. The first four eigensurfaces for product functional principal component analysis are depicted, with ϕ₁(t)ψ₁(s) (top left, 13.62%), ϕ₂(t)ψ₁(s) (top right, 8.62%), ϕ₁(t)ψ₂(s) (bottom left, 3.65%) and ϕ₂(t)ψ₂(s) (bottom right, 1.50%) as per (5), where the percentages represent the fraction of variance explained by the respective eigensurface and the ϕ_j are the eigenfunctions reflecting the variation over the age span in days while the ψ_k are the eigenfunctions for the intra-day variation. The x-axis indicates the age coordinate t (measured in days) and the y-axis represents the hour coordinate s within a given day (0–24 hours). Only flies surviving 32 days are included in this analysis.