pub(crate) fn sphere_kernel_real(grid: &Grid, radius: f64) -> Vec<f64>Expand description
sphere_kernel(matrix_size, voxel_size, radius) with the mSMV release’s sphere_kernel.m
(real(fftn(fftshift(Sphere)))): the real part of the FFT of sphere_kernel_sparse, in
double, as SMV.m builds it from a radius (SMV(x, matrix_size, voxel_size, r)).