Description of the error
Velocity interpolation order 1 and 2 are equivalent. This occurs because of the order=1 and order=2 numerical derivatives are equivalent in MDANSE.
Suggested fix
Remove the order=1 numerical derivatives or add an actual first order derivative method either forward or backward.
Additional details
Here is what you see if you run VACF with order=1, order=2 or order=3. order=1 and 2 are exactly the same while order=3 is slightly different.
Also the documentation for the 1st order velocity is not the same as what is done in the code above. The code and/or documentation needs to be corrected.
Description of the error Velocity interpolation order 1 and 2 are equivalent. This occurs because of the order=1 and order=2 numerical derivatives are equivalent in MDANSE.
see MDANSE/Mathematics/Signal.py
Suggested fix Remove the order=1 numerical derivatives or add an actual first order derivative method either forward or backward.
Additional details Here is what you see if you run VACF with order=1, order=2 or order=3. order=1 and 2 are exactly the same while order=3 is slightly different.
order=1![image](https://github.com/ISISNeutronMuon/MDANSE/assets/14276033/2265eb73-7ce8-4e10-8354-c68529b83e7b)
order=2![image](https://github.com/ISISNeutronMuon/MDANSE/assets/14276033/dfa93e3a-e99c-40d0-941f-6a327000a52e)
order=3![image](https://github.com/ISISNeutronMuon/MDANSE/assets/14276033/b7086eae-18d8-47f1-a370-0d49d436eb30)