  Dynamical low-rank (DLR) approximation methods have previously been developed
for time-dependent radiation transport problems. One crucial drawback of DLR is
that it does not conserve important quantities of the calculation, which limits
the applicability of the method. Here we address this conservation issue by
solving a low-order equation with closure terms computed via a high-order
solution calculated with DLR. We observe that the high-order solution well
approximates the closure term, and the low-order solution can be used to
correct the conservation bias in the DLR evolution. We also apply the linear
discontinuous Galerkin method for the spatial discretization to obtain the
asymptotic limit. We then demonstrate with the numerical results that this
so-called high-order / low-order (HOLO) algorithm is conservative without
sacrificing computational efficiency and accuracy.
