Wiggle-less prior and corresponding SELFI posterior on the initial matter power spectrum θ. The prior mean θ₀, also used as expansion point, is indicated by the yellow line; its 2σ credible region corresponds to the yellow-shaded area. The posterior mean γ and 2σ credible region correspond to the green line and shaded area. The ground truth θ_gt is indicated by the solid blue line. The dashed red line denotes the Nyquist frequency. Even though the prior contains no information about the BAOs, the SELFI posterior is consistently unbiased across all scales and accurately retrieves the oscillations up to k ≃ 0.2 h/Mpc.