Centrality dependence of $\rho_{n,mk}$ in Pb--Pb collisions at $\sqrt{s_{_{\rm NN}}} = 2.76$ TeV. ATLAS measurements based on the event-plane correlation  are presented with open markers. The hydrodynamic calculations from ${\tt IP}$-${\tt Glasma+MUSIC+UrQMD}$  are shown with open bands.