Function apply_medi_operator_core 

fn apply_medi_operator_core(
    fft_ws: &mut Fft3dWorkspaceF32,
    bufs: &mut MediOpBuffers<'_>,
    n: usize,
    nx: usize,
    ny: usize,
    nz: usize,
    vsx: f32,
    vsy: f32,
    vsz: f32,
    dx: &[f32],
    w: &[Complex32],
    d_kernel: &[f32],
    mx: &[f32],
    my: &[f32],
    mz: &[f32],
    vr: &[f32],
    lambda: f32,
    out: &mut [f32],
)

Apply MEDI operator in-place: out = fidelity(dx) + lambda*reg(dx) This is the hot path - called many times per Gauss-Newton iteration Uses per-direction gradient masks (mx, my, mz) matching MATLAB MEDI SIMD-accelerated for element-wise operations