Reference.Variables.time.steps

Variable "time.steps" in MATLAB/Octave version of WavePacket

For the source code of this classdef see here.

For a better understanding of the following parameters, note that there are two types of time steps. Main time steps are time intervals after which certain actions are done: expectation values of observables are calculated, and optionally the densities (from wave functions or trajectories) are plotted and/or saved. This has to be distinguished from the substeps or propagation time steps which are usually much smaller. They give the time stepping (time discretization) for actually propagating the wave functions or trajectories using the split-operator or differencing schemes called in qm_propa. An exception are the (real or imaginary time) Chebychev propagators (class "wave" only) which do not use substeps.

For a more in-depth explanation of how to optimally choose the time steps, along with a discussion of truncating the Hamiltonian in WavePacket, the interested reader is referred to our Wiki page on these issues.

Settable parameters

property	explanation	default
m_start	Index of first main time step	0
m_stop	Index of last main time step	1
m_delta	Size of main time steps	1
s_number	Number of substeps per main time step	1

The same time stepping scheme is also used for (Runge-Kutta and related) ODE solvers implemented in qm_optimal. In contrast, when using the (Runge-Kutta or other) ODE solvers implemented in qm_propa the time substeps are determined adaptively; there the substeps provided by the user are only used to plot the (usually fast) time dependence of the electric fields. Note that the parameters for the ODE solvers can be found in variable control.solvers.

Internal variables

property	explanation
m_number	Total number of main time steps
t_total	Total simulation time
s_delta	Size of time substeps
m_grid	Array of all main time steps
s_grid	Array of all time substeps
m_alpha	Kosloff alpha number wrt main time step size (used in the Chebychev expansion)
s_alpha	Kosloff alpha number wrt time substep size (used in the Chebychev expansion)
acf	Autocorrelation function (class "wave" only)
freq	Frequencies of absorption spectrum obtained from acf (class "wave" only)
spec	Intensities of absorption spectrum obtained from acf (class "wave" only)