Abstract: |
Many investment models in discrete or continuous-time settings boil down to
maximizing an objective of the quantile function of the decision variable.
This quantile optimization problem is known as the quantile formulation of the
original investment problem. Under certain monotonicity assumptions, several
schemes to solve such quantile optimization problems have been proposed in the
literature. In this paper, we propose a change-of-variable and relaxation
method to solve the quantile optimization problems without using the calculus
of variations or making any monotonicity assumptions. The method is
demonstrated through a portfolio choice problem under rank-dependent utility
theory (RDUT). We show that solving a portfolio choice problem under RDUT
reduces to solving a classical Merton's portfolio choice problem under
expected utility theory with the same utility function but a different pricing
kernel explicitly determined by the given pricing kernel and probability
weighting function. With this result, the feasibility, well-posedness,
attainability and uniqueness issues for the portfolio choice problem under
RDUT are solved. The method is applicable to general models with law-invariant
preference measures including portfolio choice models under cumulative
prospect theory (CPT) or RDUT, Yaari's dual model, Lopes' SP/A model, and
optimal stopping models under CPT or RDUT. |