Propagator.m

Calculates exponential propagators. Syntax:

           P=propagator(spin_system,L,timestep)

returns exp(-i*L*t). The following calculation methods are supported:

  'cpu'       - Taylor series with scaling and squaring
                on CPU, spmd parallel if possible

  'gpu'       - Taylor series with scaling and squaring
                on GPU

The propagator calculation method is chosen by setting the sys.enable parameter during the call to create.m function.

Notes: we did have Chebyshev and Newton series here at one point, as well as the Pade method. None of them has lived up to their marketing.