Symbolic inner products test does not pass with sympy>=1.9

[jodemaey]

Since the new versions of Sympy, the symbolic inner products test does not pass:

Above you can see the result of the test with Sympy 1.9 .

If you use the symbolic inner products with qgs, you need to install the version 1.8 of Sympy to avoid any problems. Please also consider running the tests yourself on your machine to be sure that you can trust the model output.

A first simple patch will be provided asap, simply enforcing Sympy 1.8 in the requirements.

We are working on a definitive solution to this issue but this may take some weeks.

[jodemaey]

The quick temporary fix was released with the commit fc4faed

[jodemaey]

A final bugfix was merged in master branch today.
Basically this bug was due to Sympy probably being now more cautious in substitution of variables, and this impacted the setting of the aspect ratio parameter in the symbolic inner products. This has been solved by being more rigorous in coding this parameter substitutions in the symbolic inner products.

Impact for the users

Actually, most of the example notebooks and scripts using the symbolic inner products were not impacted by this bug because it only happened if you defined the symbolic basis before setting the model domain aspect ratio, which none of the said scripts and notebooks did. So in general users were not impacted by this bug and can trust their previous model outputs, unless they played with the aspect ratio at various points in their scripts.

Users who want more details or verifications can contact me directly (@jodemaey).