My application requires it because I am computing the Q factor based on depencance of total energy on time. I have been trying to do in with the meep::do_harminv and the methods explained on http://ab-initio.mit.edu/wiki/index.php/Meep_C-plus-plus_Tutorial but It simply does not work for me. I was trying with different positons of probes, different ranges a.s.o. but every time I am getting strange results, every time different Q's on every probe, sometimes negative ones too, with strange frequencies that should not appear there. But when I just keep track of total energy and then fit a function to it by myself I get good results for Q so it means the setup is ok and the calculation of Q from E works. The one from fields on specific points somehow does not.
I think it would be anyways very useful to have a totaly separate specialized routine for calculating the total energy. Or even better would be if it was calculated automaticaly during every time step as a side product of FDTD calculation. This way it should not slow down the calculation more then few percent and if there was an option to turn it off or on in the fields class constructor it would be perfect. Thomas Jefferson 2008/7/29 Steven G. Johnson <[EMAIL PROTECTED]>: > On Jul 28, 2008, at 12:19 AM, Jefferson Thomas wrote: >> double ex = fields->field_energy_in_box(meep::Ex, >> volume.surroundings()); >> double ey = fields->field_energy_in_box(meep::Ey, >> volume.surroundings()); >> double ez = fields->field_energy_in_box(meep::Ez, >> volume.surroundings()); >> double hx = fields->field_energy_in_box(meep::Hx, >> volume.surroundings()); >> double hy = fields->field_energy_in_box(meep::Hy, >> volume.surroundings()); >> double hz = fields->field_energy_in_box(meep::Hz, >> volume.surroundings()); > > Note that this is only first-order accurate, because it combines the E > and H field energy from different times (because the H field is offset > in time from E). See also: > > http://ab-initio.mit.edu/wiki/index.php/Synchronizing_the_magnetic_and_electric_fields > > for how to synchronize the fields before computing the energy. > > The reason that this is still fairly slow is that the energy-in-box > routine is implemented using a very general field-integration function > that supports integration of arbitrary user-defined functions of > multiple field components over arbitrary volumes in the grid. This > generality comes at a price. (Although it could probably be optimized > much more. e.g. looking at the total_energy routine, I noticed that > it performs integrals of some field components even in cases when it > could easily figure out a priori that they are zero.) > > A specialized integration routine just for the field energy would > certainly be far faster. Especially for a routine just to compute the > total field energy over the entire grid. Especially if you want to > add specialized code to your timestepping routines to keep track of > this information as you update the fields. > > However, generality has been a much higher priority in Meep that > optimizing particular functions that are normally not performance > sensitive. e.g. I'm not sure what circumstance you are in that you > need to calculate the total field energy in the grid at every time > step, but it is pretty unusual in my experience; normally you need > such integrals only every several timesteps at most. Could you say > something about why your application requires this? > > Steven > > _______________________________________________ > meep-discuss mailing list > [email protected] > http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss > _______________________________________________ meep-discuss mailing list [email protected] http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
