It is Matlab/System issue to load FDTD files. Lumerical software is designed and well tested for its own script. However, for 3rd party tools, we may not do thoroughfully test to fully utilize their functionalities. I would suggest that you do not use matlab function. Instead, run FDTD in the main code and see if it can successfully work as expected.
In addition, matlab R2021a is not officially tested for integration purpose at Lumerical. Please visit this page https://support.lumerical.com/hc/en-us/articles/360026142074-MATLAB-script-integration-configuration-guide
In addition, matlab R2021a is not officially tested for integration purpose at Lumerical. Please visit this page https://support.lumerical.com/hc/en-us/articles/360026142074-MATLAB-script-integration-configuration-guide
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