Re: [Cppqed-support] Problem with fuzzy time bugfix

[Andras V. <and...@ui...>]

Dear Raimar,

All right, I seem to understand everything. I have merged and pushed,
so everyone can update now, and you can also remove your bugfix
branch. Thanks for clarifying this.

> (*) Actually the stepsize can only decrease in the case ha_==0, li_!=0, which
> might be inefficient. Maybe we should consider to increase the stepsize if
> dpLimit is undershot significantly? Take for example a driven three level atom
> in V configuration with a strong transition and a metastable excited state
> (optical shelving). In periods where many photons are scattered we need a
> small timestep, but when the atom is "shelved" larger timesteps are sufficient.

Yes, it's definitely a problem that the timestep can only decrease in
this case. In the case of ha_=0, we should completely delegate
timestep management to the Liouvillean part, so that it can also
increase the timestep.

What we need is this:
* timestep can increase if both the Hamiltonian and the Liouvillean
agree with this
* timestep should decrease if either requires this
(if either ha_ or li_ is 0, it always agrees with an increase and
never requires a decrease)
* timestep should be Dt if both ha_ and li_ are 0, in which case the
dc!=0 case doesn't even make sense, really (so this should maybe be
filtered out when constructing MCWF_Trajectory)

Best regards,
András