Note: This issue only affects GPU simulations on Ansys Lumerical FDTD™ 2025 R2. This issue does not affect simulations run on CPU, or does it affect any previously released versions of the software.
Issue Description
In Ansys Lumerical FDTD™ 2025 R2, explicitly saving simulations in analysis mode after a GPU simulation completes causes monitors to lose results when you reload the file. This issue can affect parameter sweeps.
Common sources of saving the file in analysis mode are listed below:
- Clicking on the “Save” button in the “File” tab
- Pressing the Ctrl+S shortcut
- Prompted by calculation of the mode expansion monitor
- Prompted when an analysis script is edited
This issue does not affect results within an analysis group.
Workaround
You can avoid this issue by immediately renaming the .fsp file after simulation and appending a ‘0’ to the end of the file name, without re-saving it explicitly.
For example, if your file is named mySim.fsp, rename it to mySim0.fsp without saving after simulation completes.
Note: After simulation completes, the file automatically saves once. Therefore, even if you close the file for renaming without explicitly saving, that file still has all simulation results.
We recommend that you make the renamed file a copy, rather than replacing the original file, in order to prevent issues with future versions.
You can then freely modify the renamed file.
A Lumerical script is provided below to accomplish this. However, you can also do this through other tools like command line, Python, or Windows File Explorer.
#Run command, setup is before this
run(‘FDTD’, ‘GPU’);
#Immediately rename the file and make a copy
tmp_filename = currentfilename;
new_filename = substring(tmp_filename, 1,length(tmp_filename)-4) + ”0.fsp”;
newproject;
cp(tmp_filename, new_filename); #Make copy to avoid issues with future versions
load(new_filename); #Load the renamed file, you can now freely modify this file