pub fn fansi_unit_ee2(dims: (usize, usize, usize)) -> Vec<f64>Expand description
FANSI’s EE2 = |E1|^2 + |E2|^2 + |E3|^2 with E_j = 1 - exp(2*pi*i*k_j/N_j): the
spectral Laplacian of unit-spacing forward differences, as FANSI’s nlTV.m, nlTGV.m and
nlL1TV.m build it (whatever the voxel size). Pair it with fgrad_inplace/bdiv_inplace
on a unit-voxel grid. FFT order, i + nx*(j + ny*k).