Power spectrum of the simulation volume at its initial condition (z ∼ 127). Blue shows the power of the constrained field (large scales) in the 34 × 28 × 450 cMpc³/h³ volume. Orange shows the theoretically expected linear power. The shaded region shows the composite realization for the cosmosTNG simulations: modes are from the constrained field up to k_cutoff = 1 h/cMpc above which we randomly draw modes according to linear theory.