Function cg_solve 

fn cg_solve(
    ws: &mut Ws,
    d_kernel: &[f32],
    wf2: &[f32],
    wr2: &[f32],
    mmx: &[f32],
    mmy: &[f32],
    mmz: &[f32],
    mrx: &[f32],
    mry: &[f32],
    mrz: &[f32],
    vr_tot: &[f32],
    vr_pos: &[f32],
    vr_neg: &[f32],
    lambda1: f32,
    field_w: f32,
    cf_ppm: f32,
    dr_p: f32,
    dr_q: f32,
    mask: &[u8],
    b: &[f32],
    x: &mut [f32],
    stage: &mut [f32],
    r: &mut [f32],
    p: &mut [f32],
    ap: &mut [f32],
    tol: f32,
    max_iter: usize,
)

Standard CG on the doubled system.