  We investigate the flexibility of the entropy (topological and metric) for
the class of piecewise expanding unimodal maps. We show that the only
restrictions for the values of the topological and metric entropies in this
class are that both are positive, the topological entropy is at most $\log 2$,
and by the Variational Principle, the metric entropy is not larger than the
topological entropy.
  In order to have a better control on the metric entropy, we work mainly with
topologically mixing piecewise expanding skew tent maps, for which there are
only 2 different slopes. For those maps, there is an additional restriction
that the topological entropy is larger than $\frac{1}{2}\log2$.
  We also make the interesting observation that for skew tent maps the sum of
reciprocals of derivatives of all iterates of the map at the critical value is
zero. It is a generalization and a different interpretation of the
Milnor-Thurston formula connecting the topological entropy and the kneading
determinant for unimodal maps.
