HDiv boundary recovery not working for vector function spaces #691
Description
We saw some odd behaviour with lop-sided bubbles (see #688). I tracked this down to the HDiv boundary recovery, which involves:
- separating the vector field into scalar components
- performing the boundary recovery on the scalar components
- recombining the scalar components to obtain a vector
This process of separating and recombining components uses interpolation -- and this seems to be the issue:
- if I comment out the boundary recovery, the bubble is still lop-sided
- if I use a projection instead of interpolation, the bubble looks good
This needs understanding and fixing! #688 got away from this by turning off the HDiv boundary recovery