  Most common Optimal Transport (OT) solvers are currently based on an
approximation of underlying measures by discrete measures. However, it is
sometimes relevant to work only with moments of measures instead of the measure
itself, and many common OT problems can be formulated as moment problems (the
most relevant examples being $L^p$-Wasserstein distances, barycenters, and
Gromov-Wasserstein discrepancies on Euclidean spaces). We leverage this fact to
develop a generalized moment formulation that covers these classes of OT
problems. The transport plan is represented through its moments on a given
basis, and the marginal constraints are expressed in terms of moment
constraints. A practical computation then consists in considering a truncation
of the involved moment sequences up to a certain order, and using the
polynomial sums-of-squares hierarchy for measures supported on semi-algebraic
sets. We prove that the strategy converges to the solution of the OT problem as
the order increases. We also show how to approximate linear quantities of
interest, and how to estimate the support of the optimal transport map from the
computed moments using Christoffel-Darboux kernels. Numerical experiments
illustrate the good behavior of the approach.
