This function estimates the norm of the Liouvillian supplied and returns the time step that ensures monotonic convergence of the powder series in the exponential propagator. From the numerical accuracy point of view, this is the optimal time step for the evolution. Syntax:
L - Liouvillian operator or superoperator inder which the evolution is taking place.
interval - the total evolution time, must be specified if the op- timal number of steps is also wanted in the output.
timestep - optimal time step
nsteps - number of steps covering the interval, if the interval was specified
Note: if a zero Liouvillian is supplied, the function would return the following values: timestep=0, nsteps=1