  We study an optimal liquidation problem under the ambiguity with respect to
price impact parameters. Our main results show that the value function and the
optimal trading strategy can be characterized by the solution to a semi-linear
PDE with superlinear gradient, monotone generator and singular terminal value.
We also establish an asymptotic analysis of the robust model for small amount
of uncertainty and analyse the effect of robustness on optimal trading
strategies and liquidation costs. In particular, in our model ambiguity
aversion is observationally equivalent to increased risk aversion. This
suggests that ambiguity aversion increases liquidation rates.
