  The second and the third order anisotropic flow, $V_{2}$ and $V_3$, are
determined by the corresponding initial spatial anisotropy coefficients,
$\varepsilon_{2}$ and $\varepsilon_{3}$, in the initial density distribution.
On the contrary, the higher order anisotropic flow $V_n$ ($n > 3$), in addition
to their dependence on the same order initial anisotropy coefficient
$\varepsilon_{n}$, have a significant contribution from lower order initial
anisotropy coefficients, which leads to mode-coupling effects. In this
contribution, we present the investigations on linear and non-linear modes in
higher order anisotropic flow ($V_{4}$, $V_{5}$ and $V_{6}$) in Pb--Pb
collisions at $\sqrt{s_{\rm NN}} =$ 2.76 TeV using the ALICE detector at the
Large Hadron Collider (LHC). A significant contribution from a non-linear mode
is observed. A new observable, the non-linear response coefficient, is measured
as well. The comparison to theoretical calculations provides crucial
information on dynamic of the created system especially at the freeze-out
conditions, which are poorly known from previous flow measurements.
