A trial to switch back to numpy arrays for performance. We do not even really use any xarray features currently.
For the cascading reservior example, which also does some calculations, this results in approx. 3x speedup.
Todo
Get rid of xarray
Rename to_xarray() (renamed to prepare())
Rename xdata args
Update the book
Update the homepage
Benchmarks
When comparing columns, keep in mind that pushing xarray data basically requires creating the underlying numpy data first.
So the most frequent use case is comparing first vs. last column.
However, even compared to pushing xarray data we get quite some speedup for larger data.
