I encountered an issue with the add_design method in the doepandas package when specifying resolutions for fractional factorial designs with 6 factors. The method allows for the selection of a resolution that is not standard, resulting in an error.

Issue Details:
When attempting to create a design with resolution=VI for 6 factors, the method fails with a ValueError indicating "design not possible." But when setting resolution=V for 6 factors, the design given is with 32 runs. Although, resolution V does not typically exist for 6 factors in standard design tables.

Standard Resolutions:
For 6 factors, the standard resolutions are:
Resolution IV: 16 runs (1/4 fraction of the full factorial)
Resolution VI: 32 runs (1/2 fraction of the full factorial)

Expected Behavior:
The method should either generate a valid design for compatible resolutions or provide a descriptive error message indicating that the requested resolution is not valid for the given number of factors.

Hello, I'm trying to use this package in a python 3.12 environment, but am getting the following error:

ModuleNotFoundError: No module named 'imp'

It looks like imp was dropped in favor of importlib in python 3.12. Are there any plans to offer 3.12 compatibility, or any other workarounds?

Thanks!

This PR contains the refactor and tests of fractfact. It could be nice to re-integrate the relevant changes in pyDOE3.

Error in CI tests

All done! ✨ 🍰 ✨
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Hi @relf,

first of all thank you for keeping pyDOE up-to-date! I have an issue with the function fracfact_opt

complaining about n_aliases being a float instead of an int

and hashing the numpy arrays gives me an error here:

Not sure what the best solution for hashing is. Maybe just contrast.tobytes()?

I use python 3.11.9 and numpy 1.26.4.