fn sphere_kernel(
grid: &Grid,
radius: f64,
fft: &mut Fft3dWorkspace,
) -> Vec<Complex64> ⓘExpand description
sphere_kernel.m as MEDI_L1.m and extract_CSF.m use it here: fftn(fftshift(Sphere))
in double, complex (the MEDI toolbox’s sphere_kernel.m before the mSMV release added
real(...); the two differ only on odd grids, which medi pads away)