BUG in spectral operator with OUTFLOW bounday condition
I get a size mismatch when using spectral diffusion (same with poisson).
ValueError: filter_diffusion_3d: Output operand 0 has a mismatch in its core dimension 1, with gufunc signature (n,m,p),(n),(m),(p),()->(n,m,p) (size 126 is different from 128)
See file : test_diffusion_bc.py