SummationByParts/sbp/src/operators/upwind4h2.rs

use super::{
    diff_op_col, diff_op_row, SbpOperator1d, SbpOperator2d, UpwindOperator1d, UpwindOperator2d,
};
use crate::Float;
use ndarray::{ArrayView1, ArrayView2, ArrayViewMut1, ArrayViewMut2};

#[derive(Debug, Copy, Clone)]
pub struct Upwind4h2;

impl Upwind4h2 {
    #[rustfmt::skip]
    const HBLOCK: &'static [Float] = &[
        0.91e2/0.720e3, 0.325e3/0.384e3, 0.595e3/0.576e3, 0.1909e4/0.1920e4,
    ];
    #[rustfmt::skip]
    const DIAG: &'static [Float] = &[
        -1.43229166666667e-02, 1.40625000000000e-01, -7.38281250000000e-01, 0.00000000000000e+00, 7.38281250000000e-01, -1.40625000000000e-01, 1.43229166666667e-02
    ];
    #[rustfmt::skip]
    const BLOCK: &'static [&'static [Float]] = &[
        &[-3.95604395604396e+00, 5.41758241758242e+00, -1.94505494505495e+00, 4.83516483516484e-01],
        &[-8.09025641025641e-01, 0.00000000000000e+00, 1.03948717948718e+00, -2.47384615384615e-01, 1.69230769230769e-02],
        &[2.37983193277311e-01, -8.51680672268908e-01, 0.00000000000000e+00, 7.35966386554622e-01, -1.36134453781513e-01, 1.38655462184874e-02],
        &[-6.14632442814737e-02, 2.10581456259822e-01, -7.64623712240265e-01, 0.00000000000000e+00, 7.42535358826611e-01, -1.41435306443164e-01, 1.44054478784704e-02],
    ];

    #[rustfmt::skip]
    const DISS_BLOCK: &'static [&'static [Float]] = &[
        &[-2.76989342315976e-01, 5.19355016842454e-01, -3.46236677894969e-01, 1.03871003368491e-01],
        &[7.75570158484731e-02, -1.62342481638964e-01, 1.47715500579822e-01, -7.98531117124082e-02, 1.69230769230769e-02],
        &[-4.23630758836198e-02, 1.21027405937249e-01, -1.91609307039399e-01, 1.82272708078206e-01, -8.31932773109244e-02, 1.38655462184874e-02],
        &[1.32037874021759e-02, -6.79734450144910e-02, 1.89370108794365e-01, -2.78654929966754e-01, 2.16081718177056e-01, -8.64326872708224e-02, 1.44054478784704e-02],
    ];

    #[rustfmt::skip]
    const DISS_DIAG: &'static [Float; 7] = &[
        1.43229166666667e-02, -8.59375000000000e-02, 2.14843750000000e-01, -2.86458333333333e-01, 2.14843750000000e-01, -8.59375000000000e-02, 1.43229166666667e-02,
    ];
}

impl SbpOperator1d for Upwind4h2 {
    fn diff(&self, prev: ArrayView1<Float>, fut: ArrayViewMut1<Float>) {
        super::diff_op_1d(Self::BLOCK, Self::DIAG, false, true, prev, fut)
    }

    fn h(&self) -> &'static [Float] {
        Self::HBLOCK
    }
    fn is_h2(&self) -> bool {
        true
    }
}

impl<SBP: SbpOperator1d> SbpOperator2d for (&SBP, &Upwind4h2) {
    fn diffxi(&self, prev: ArrayView2<Float>, mut fut: ArrayViewMut2<Float>) {
        assert_eq!(prev.shape(), fut.shape());
        assert!(prev.shape()[1] >= 2 * Upwind4h2::BLOCK.len());

        match (prev.strides(), fut.strides()) {
            ([_, 1], [_, 1]) => {
                diff_op_row(Upwind4h2::BLOCK, Upwind4h2::DIAG, false, true)(prev, fut);
            }
            ([1, _], [1, _]) => {
                diff_op_col(Upwind4h2::BLOCK, Upwind4h2::DIAG, false, true, prev, fut);
            }
            ([_, _], [_, _]) => {
                // Fallback, work row by row
                for (r0, r1) in prev.outer_iter().zip(fut.outer_iter_mut()) {
                    Upwind4h2.diff(r0, r1);
                }
            }
            _ => unreachable!("Should only be two elements in the strides vectors"),
        }
    }
}

impl<UO: UpwindOperator1d> UpwindOperator2d for (&UO, &Upwind4h2) {
    fn dissxi(&self, prev: ArrayView2<Float>, mut fut: ArrayViewMut2<Float>) {
        assert_eq!(prev.shape(), fut.shape());
        assert!(prev.shape()[1] >= 2 * Upwind4h2::BLOCK.len());

        match (prev.strides(), fut.strides()) {
            ([_, 1], [_, 1]) => {
                diff_op_row(Upwind4h2::DISS_BLOCK, Upwind4h2::DISS_DIAG, true, true)(prev, fut);
            }
            ([1, _], [1, _]) => {
                diff_op_col(
                    Upwind4h2::DISS_BLOCK,
                    Upwind4h2::DISS_DIAG,
                    true,
                    true,
                    prev,
                    fut,
                );
            }
            ([_, _], [_, _]) => {
                // Fallback, work row by row
                for (r0, r1) in prev.outer_iter().zip(fut.outer_iter_mut()) {
                    Upwind4h2.diss(r0, r1);
                }
            }
            _ => unreachable!("Should only be two elements in the strides vectors"),
        }
    }
}

#[test]
fn upwind4h2_test() {
    let nx = 20;

    let x = crate::utils::h2linspace(0.0, 1.0, nx);

    let mut res = ndarray::Array1::zeros(nx);

    Upwind4h2.diff(x.view(), res.view_mut());
    let ans = &x * 0.0 + 1.0;
    approx::assert_abs_diff_eq!(&res, &ans, epsilon = 1e-4);

    res.fill(0.0);
    let y = &x * &x / 2.0;
    Upwind4h2.diff(y.view(), res.view_mut());
    let ans = &x;
    approx::assert_abs_diff_eq!(&res, &ans, epsilon = 1e-4);

    res.fill(0.0);
    let y = &x * &x * &x / 3.0;
    Upwind4h2.diff(y.view(), res.view_mut());
    let ans = &x * &x;
    approx::assert_abs_diff_eq!(&res, &ans, epsilon = 1e-2);
}

impl UpwindOperator1d for Upwind4h2 {
    fn diss(&self, prev: ArrayView1<Float>, fut: ArrayViewMut1<Float>) {
        super::diff_op_1d(Self::DISS_BLOCK, Self::DISS_DIAG, true, true, prev, fut)
    }

    fn as_sbp(&self) -> &dyn SbpOperator1d {
        self
    }
}