Partial Derivative with respect to system parameter not implemented in .diff utility [BUG] about heyoka

[guescrib]

There's a very simple workaround to this issue: include the parameter as an additional state variable with no dynamics. Nonetheless we think it could make sense to include this feature in order to differentiate between parameters and system variables... Anyway if there is not a quick/easy fix probably the issue can be resolved without any additional action...

[bluescarni]

Indeed derivatives wrt parameters are not currently available. I plan to add them eventually, but this requires some refactoring of the differentiation code, thus it will take some time.

The workaround you mention is correct. Another possible approach is to convert the expression to sympy (where parameters are transformed into variables called par[n]), do the differentiation and then convert back to heyoka expressions (where par[n] will be converted back into a param).

There is a tutorial about sympy interconversion here:

https://bluescarni.github.io/heyoka.py/notebooks/sympy_interop.html

[bluescarni]

It is now possible to compute derivatives wrt parameters, see #196. This feature will be available in the upcoming 0.15 version.

Closing the report.