Learning Forum

[Taylor Robertson]

When you run a simulation in FDTD the job manager window shows the auto shutoff level, which is a measure of the energy left in the simulation window. This value is used to determine if the calculation can be stopped before the end of the simulation time. In some cases it might happen that the job manager shows the value of the auto shutoff to be 1 or some value smaller than 1 but larger than the minimum from the simulation settings (1e-5 by default) and then the simulation suddenly stops. This does not necessarily mean that the simulation did not reach the condition for early shutoff. If the log file created during the simulation shows the following message:

“Early termination of simulation, the autoshutoff criteria are satisfied.”

your simulation has stopped properly. The reason why you might encounter this unexpected termination is because the condition for ending the simulation was reached before the job manager had time to update the displayed value for the auto shutoff level. This value is updated every ~1% of the simulation time; therefore, if the simulation time (from the simulation settings) is long compared to the time it takes the energy to leave the simulation window, you might not be able to see the shutoff level decreasing nicely to the minimum. This, however, does not mean that there is something wrong with the simulation, it is just a consequence of the way the information in the job manager is updated.

It is not possible to modify the job manager settings for showing the auto shutoff level, for example to be every 0.1% of the simulation time. However, you have control over the internal sample time for the auto shutoff in the “Advanced options” tab of the “Edit FDTD simulation” window. The default setting is to internally check the auto shutoff conditions every 100 time steps of the simulation; usually, this is a very small fraction of the total simulation time, smaller than 1%, and so the program will internally check the condition for autoshutoff more frequently than what you see in the job manager.