Admissible Discrete Linear Propagators for High-Order Time Splittings of Rotational Nonlinear Schrödinger Equations with Arbitrary Three-Dimensional Rotation
For computational scientists solving rotational nonlinear Schrödinger equations, this work provides a fix to a previously unrecognized order-reduction issue, enabling reliable high-order time integration.
The authors identify a defect mechanism in high-order time splittings for rotational nonlinear Schrödinger equations that causes state-dependent order reduction, and construct two admissible discrete linear propagators that restore the designed high-order accuracy (second, fourth, sixth).
We study robust high-order time splittings for nonlinear Schrödinger equations whose linear part is defined by the Laplacian and an arbitrary three-dimensional rotation operator. After Fourier pseudospectral discretization, a continuous exact factorization of the linear flow need not yield a method self-adjoint fixed-grid propagator. For the original stage-wise explicit exact integrator, we identify a quadratic even term in the local logarithm and show that its visibility is state-dependent, so the observed temporal order of accuracy can depend on the initial data. We then formulate fixed-grid admissibility for discrete linear propagators and construct two admissible propagators for arbitrary three-dimensional rotation: a symmetrized explicit exact integrator and a palindromic generalized shear propagator. Both are unitary, first-order consistent, method self-adjoint, and have odd local logarithms. Numerical experiments verify the predicted defect mechanism and demonstrate recovery of the designed second-, fourth-, and sixth-order behavior with the admissible propagators.