Function compute_smv_fft 

fn compute_smv_fft(
    nx: usize,
    ny: usize,
    nz: usize,
    vsx: f64,
    vsy: f64,
    vsz: f64,
    radius: f64,
) -> Vec<f64>

Compute FFT of SMV kernel (returns real part, since kernel is symmetric)