Seems that we have got the PDE check passed again. Content of output `check_pde.dat`: | no. | 1 | 2 | 3 | 4 | |---------- | ----------- | ----------- | ----------- | -----------| |h | 0.1 | 0.01 | 0.001 | 0.0001 | |residual_u | 0.264407 | 0.000264403 | 4.94253e-07 | 3.97963e-05| |residual_v | 1.76263e-05 | 1.76271e-08 | 3.29687e-11 | 2.55261e-09| cc @inducer

Very cool! How does the PDE do if the volume potential is included? (You should be able to just specify `cp.points` as `targets` for the VP eval.)