adding information on how to avoid creating a expanded copy when call… (#27)

adding information on how to avoid creating an expanded copy when calling monitor data

Author: FilipeFcp

_faqs/why-does-the-kernel-crash-sometimes-when-using-the-web-based-python-notebook.md

@@ -4,4 +4,12 @@ date: 2023-10-24 18:09:43
 enabled: true
 category: 'Simulation Troubleshoot'
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-The web-based Python notebook environment in `tidy3d.simulation.cloud` only has access to 4 GB of memory. When running a large simulation or complex optimizations, the memory needed to process the data could exceed the limit, causing the kernel to crash. In this case, we recommend installing `Tidy3D` on your local computer by following the installation [guide](https://docs.flexcompute.com/projects/tidy3d/en/latest/install.html) and [video](https://youtu.be/qQidx65Jmu0). It will then use your computer memory, which is typically larger than 4 GB.
+The web-based Python notebook environment in `tidy3d.simulation.cloud` only has access to 8 GB of memory. When running a large simulation or complex optimizations, the memory needed to process the data could exceed the limit, causing the kernel to crash. In this case, we recommend installing `Tidy3D` on your local computer by following the installation [guide](https://docs.flexcompute.com/projects/tidy3d/en/latest/install.html) and [video](https://youtu.be/qQidx65Jmu0). It will then use your computer memory, which is typically larger than 8 GB.
+
+If [symmetries](https://www.flexcompute.com/tidy3d/examples/notebooks/Symmetry/) are not used in the simulation, memory usage can be reduced by calling `data = sim_data.monitor_data['monitor_name']` instead of `data = sim_data['monitor_name']`. The latter creates a copy of the monitor data and expands it to include the symmetric parts, if applicable.
+
+However, if symmetries are used in the simulation, `data = sim_data.monitor_data['monitor_name']` will return data only for the simulated portion of the volume, and not the symmetric extensions. For example, if symmetry is applied in the x-plane, only half of the data will be returned.
+
+Note that many analyses can still be performed with this partial data. For instance, the mode volume can be computed using the non-expanded monitor and then multiplied by the appropriate factor (`2`, `4`, or `8` for `1`, `2`, or `3` symmetry planes, respectively). An example of this approach can be seen in [this example](https://www.flexcompute.com/tidy3d/examples/notebooks/NanobeamCavity/).
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